Understanding Reactivity and Assembly of Dichalcogenides: Structural, Electrostatic Potential, and Topological Analyses of 3 H-1,2-Benzodithiol-3-one and Selenium Analogs

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Understanding Reactivity and Assembly of Dichalcogenides:

Structural, Electrostatic Potential, and Topological Analyses of

3

H ‑1,2-Benzodithiol-3-one and Selenium Analogs

Rahul Shukla, Arun Dhaka, Emmanuel Aubert, Vishnu Vijayakumar-Syamala, Olivier Jeannin,

Marc Fourmigue,* and Enrique Espinosa*

́

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sı Supporting Information

ABSTRACT: Molecular assembly and reactivity have been investigated with a series of 3H-1,2-benzodithiol-3-(thi)one derivatives

and their (mixed) selenated analogs. Electrostatic potential calculations on monomers show three σ-hole regions around the

dichalcogenide Ch−Ch bond (Ch = S, Se), one side-on and two along the bonding direction. The topological analysis of the

electron density ρ(r) points to the weak nature of the Ch−Ch bond. σ-Hole and lone-pair regions are described in terms of charge

depletion (CD) and charge concentration (CC) sites found in the valence shell of chalcogen atoms. Whereas CD and CC sites are

2

characterized by the topological critical points of L(r) = −∇ ρ(r), their electrophilic and nucleophilic powers are measured by the

corresponding L/ρ magnitudes. In crystal structures, each chalcogen bond (ChB) involves a σ-hole region and shows a CD···CC

interaction that aligns with the internuclear direction of the atoms the CD and CC sites belong. The alignment holds simultaneously

for all of the ChB interactions in each crystal structure, indicating that CD···CC interactions drive molecular orientation in molecular

assembly. Strength of ChB is measured in terms of the topological properties of ρ(r), whereas the intensity of the electrophilic···

2

nucleophilic interaction is monitored by [(L/ρ)_C_C− (L/ρ) ]/d

. The σ-hole in side-on conformation forms the strongest

CD

CC···CD

ChB interactions in molecular assembly. Reactivity of molecules against nucleophilic attack has been investigated along each of the

three σ-hole regions by using ﬂuoride as a probe. Adducts formed along the Ch−Ch bonding direction are energetically more

favorable than in side-on conformation. At optimized geometries, the F···Ch bond (Ch = S, Se) exhibits a partial covalent character,

while it weakens concomitantly the Ch···Ch bond that also becomes of partial covalent character. In the reactivity process, the

signiﬁcant reorientation of the plane containing the chalcogen lone pairs, along with the opening, shrinking, and splitting of reactivity

2

surfaces ∇ ρ(r) = 0, is the signature of the charge redistribution that involves the nucleophilic attack.

1

. INTRODUCTION

ebselen and its analogues provided insights into the

mechanism of drug action in this class of organoselenium

Interest for the chemistry of selenium is currently experiencing

a strong revival along two diﬀerent directions, (i)

1

4

antioxidants. Selenium atoms activated by electron-with-

pharmaceutical applications of selenium-containing molecules

and, more recently, (ii) involvement of organo-selenium

derivatives as chalcogen bond donors in noncovalent σ-hole

based interactions. For example, the ebselen molecule [2-

phenyl-1,2-benzoisoselenazol-3(2H)one], which functions as

an antioxidant, has inspired a worldwide interest in the design

of glutathione peroxidase (GPx) mimics. Besides this, analysis

of the charge density around Se−N and Se−C covalent bonds

in conjunction with the Se···O chalcogen bonding modes in

5

6

drawing groups as in organic selenocyanates or in diselenides

2

,3

Received: July 13, 2020

Revised: October 23, 2020

©

XXXX American Chemical Society

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A

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2

were recently shown to act as eﬃcient chalcogen bond donors

through the electropositive area (σ-hole) they develop in the

prolongation of the covalent bonds to selenium. They are also

involved in the glutathione peroxidase- (GPx-) like catalytic

activity of ebselen. Organoselenium derivatives are also used

as reagents in synthesis, and one can mention here electro-

with sp nitrogen nucleophiles selectively opens the hetero-

cycle on the same site. This reactivity toward nucleophiles of

speciﬁcally the C1−Ch2 bond raises several questions, if one

considers the potentially much weaker Ch2−Ch3 (S−S, S−Se,

Se−Se) dichalcogenide bond.

7

Note also that the oxidation of COSS in the presence of

1

7

18

19,20

philic reagents such as N-phenylselenophthalimide for phenyl-

H O , peracetic acid or dimethyloxirane

selectively

2

8

selenation.

aﬀords the 1-oxide (or the 1,1-dioxide known as the Beaucage

reagent).

known as an eﬃcient reagent for stereospeciﬁc selenization of

H-phosphates and H-phosphonothioate diesters to aﬀord Se-

derivatized RNAs, DNAs and proteins,

21,22

In the course of our investigations of diselenide derivatives

3H-1,2-Benzothiaselenol-3-one (COSeS) is also

6

as chalcogen bond donors, we were attracted by the 3H-

benzo[1,2]dithiole-3-one and 3H-benzo[1,2]dithiole-3-thione

heterocycles and their selenium analogs shown in Scheme 1

23,24

an important issue

to overcome the problems faced in their X-ray crystallographic

2

5

Scheme 1. (a) Possible σ-Hole Regions around the

Dichalcogenide Ch2−Ch3 Bond in the 1,2-Dichalcogenole

Series and (b) Molecular Structures of Investigated

Compounds

studies. It is also reported as a potent fungicide at 1 ppm and

shows herbicidal and insecticidal activity at higher concen-

2

6

trations. Finally, COSeSe is only mentioned once in the

literature for its activity toward on lysosomes and mitochon-

dria in vitro, without any details on its synthesis.

27

Furthermore, none of the four carbonyl derivatives, i.e.

COSS, COSSe, COSeS and COSeSe, has been structurally

characterized while the electron-withdrawing carbonyl group is

expected to favor a polarization of the Ch2−Ch3 bond and

peculiar electrostatic potential distribution which could favor

chalcogen bonding interactions in the solid state with both

Ch2 and Ch3 chalcogens acting as ChB donors. Furthermore,

at variance with most reported diselenides investigated as ChB

6

donors which are symmetric (R−Se−Se−R′ with R = R′), the

compounds investigated here are not, and thus, this raises the

question of the location of the “deepest” σ-holes, between the

R1A, R1B, and R2 regions.

In the thiocarbonyl series, X-ray crystal structures have been

reported for the three CSSS, CSSSe, and CSSeS derivatives

(

CSSeSe is unknown). The 1,2-dithiole derivative CSSS

exhibits a reactivity comparable to COSS, with ring opening

2

between the CS and S−S moieties, by sp nitrogen

28

29

nucleophiles or by active methylene compounds, or with

17

with the abbreviations used in the following. Most of them

have been reported (except 3H-1,2-benzodiselenol-3-thione,

CSSeSe), either as reagent or reagent precursor in organic

synthesis or biochemistry, or for their pharmaceutical interest

selective oxidation by H O into the 1-oxide.

2 2

The work described here aims at rationalizing both the

speciﬁc reactivity and the molecular assembly in the solid-state

structures of these series of compounds, as models for many

others involving a disulﬁde or diselenide bond. For that

purpose, we have synthesized six of these eight derivatives. We

then combine the determination of their crystal structures and

analysis of the most pertinent interactions, with speciﬁc

emphasis on chalcogen bonding since it is actually present in

all of them. This will be substantiated by a thorough theoretical

investigation of the electronic density distribution ρ(r) and its

properties (electrostatic potential and topological analyses of

9

based on their antioxidant activity. They also bear some

analogy with selenium-based molecules (selenophtalic anhy-

1

0

6

11,12

13

dride, diselenides, tellurophenes

and selenophenes,

5

,14,15

and organic selenocyanates

), where proper activation of

the Se atom leads to the formation of strong electron-depleted

area in the prolongation of the two covalent bonds to Se,

known as σ-holes (Scheme 1a). We can distinguish potentially

here two types of σ-holes, those in the prolongation of the

covalent Ch2−Ch3 (Ch2, Ch3 = S, Se) bond, noted R1A and

R1B in Scheme 1a, and those in the prolongation of the C−

Ch2/Ch3 bonds, merging in the R2 region shown in Scheme

2

ρ(r) and L(r) = −∇ ρ(r)) around the dichalcogenide bond.

First, this will be carried out with optimized monomers, aimed

at unraveling the location of σ-hole regions and the most

electrophilic chalcogen atoms within the series, as a rationale

for their molecular assembly and chemical reactivity. In a

second step, intermolecular chalcogen bonding interactions

(ChB) will be analyzed in terms of the topological properties

of ρ(r) at bond critical points (BCP) between interacting

atoms in dimers extracted from the crystal structures, together

1

a. These sites are thought to control not only the initial

reactivity of such molecules toward nucleophilic attack but also

their solid-state arrangement as they can interact preferentially

with the charge-concentrated area of the same molecules

(

oxygen/chalcogen lone pairs) or with Lewis bases in

cocrystals.

2

For instance, in the carbonyl series, 3H-1,2-benzodithiol-3-

one (COSS) and 3H-1,2-benzoselenathiol-3-one (COSSe)

have recently been shown to be very good precursors for the

synthesis of persulﬁdes (RSSH), selenyl sulﬁdes (RSeSH), and

with the distribution of L(r) = −∇ ρ(r) magnitudes and the

associated critical points (CP’s) in the regions where ChB

show. Finally, the reactivity of this series of 1,2-dichalcogenoles

will be investigated in terms of the energetic stability and ρ(r)

−

hydrogen sulﬁde (H S), with ring opening between the CO

properties of their ﬂuoride adducts, with F at proximity of the

2

16

and SS (or SSe) moieties. Similarly, the reaction of COSS

dichalcogenide bond in regions where σ-holes show. The small

B

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−

size of F allows indeed for minimum steric hindrance, while

topological analyses of the electron density ρ(r) and its

−

2

the anionic character of F results in substantial nucleophilic

negative Laplacian L(r) = −∇ ρ(r) were performed with the

36

capacity.

AIMALL software. The Gaussian09 (version D.01) software

package was used for optimization and frequency calcula-

37

2

. RESULTS AND DISCUSSION

.1. Syntheses. As shown in Scheme 2, the preparation of

all molecules is based on the chalcogenation/cyclization of

tions.

Within the framework of the quantum theory of atoms in

2

38

molecules (QTAIM) developed by Bader and co-workers,

the topological analysis of ρ(r) permits to identify any bonding

interatomic interaction by the formation of a bond path

between atoms. Along this path ρ(r) is maximum with respect

to any other direction linking the nuclei. Bond critical points r_b

Scheme 2. Synthetic Procedures

(

BCPs) are placed at the intersection of bond paths and

interatomic surfaces (namely, the zero-ﬂux surfaces of ρ(r)

enclosing the atomic basins). The intensity and nature of

pairwise interactions are determined by analyzing simulta-

neously the topological properties of ρ(r) at r ’s. Hence, while

b

2

ρ and ∇ ρ measure the quantity of charge density and the

b

2

local depletion (∇ ρ > 0) or concentration (∇ ρ < 0) of ρ(r)

b

at r , the local electron potential (V ) and kinetic (G ) energy

b

densities are interpreted as the pressures exerted to localize

and to deplete the electron distribution at the interatomic

3

9

surface. The ratio |V |/G is a very useful descriptor to

b

distinguish between pure closed-shell interactions (|V |/G <

b

1

), shared-shell interactions (|V |/G > 2), and intermediate

b b

interactions with a partial (starting) covalence degree (1< |V |/

b

2

G < 2) where a local depletion of ρ(r) (∇ ρ > 0) is still

b

40

observed. Thus, the stronger the interaction, the larger the

2

ρ , V , and |V |/G quantities become, while |V |/G and ∇ ρ

monitor the nature of the interaction and the subtle eﬀects in

b

its evolving behavior.

2

The L(r) = −∇ ρ(r) function points out the regions of the

space where the electronic charge is locally concentrated (L(r)

> 0) and depleted (L(r) < 0). The L(r) function has been

2

,2′-dithiosalicylic acid or 2,2′-diselenosalicylic acid. Indeed,

41,42

treatment of 2,2′-dithiosalicylic acid with P S in dioxane

proposed as the physical basis for the VSEPR model,

and

4

10

aﬀords CSSS in 93% (at variance with the reported procedure

the iso-surface L(r) = 0 has been deﬁned as the reactivity

surface of molecules undergoing a nucleophilic attack (the

holes observed in the surface mark the regions through which

30

performed in xylene with 80% yield). Reaction of CSSS with

mercuric acetate gives COSS in 82% yield, a more direct route

than that reported from the successive treatment of CSSS with

tetrachloro-o-benzoquinone and HCl in dioxane. Note that

COSS had been also obtained by sulfuration of 2-halobenzoic

acid phenyl ester (obtained from 2-halobenzoic acid) with

38

the attack can take place). The topological analysis of L(r)

carries the characteristic critical points (CPs) of the function.

While (3,−3) and (3,+3) CPs indicate local maxima (3D-

concentration) and minima (3D-depletion) of electronic

charge, (3,−1) and (3,+1) CPs are saddle points and

correspond respectively to local 1D-depletion/2D-concentra-

tion and 2D-depletion/1D-concentration along the three main

directions of the L-distribution at CP. Because the L(r)

distribution exhibits positive and negative values, and varies

rapidly in the space, the topology of L(r) is diﬃcult to

interpret. In particular, many CPs of all types exhibit around

atoms and care should be taken in the selection of the relevant

ones for discussions involving nucleophilic (charge concen-

tration, CC) and electrophilic (charge depletion, CD) sites. As

31

3

2,33

Na S .

2

Selenation of 2,2′-dithiosalicylic acid to aﬀord COSeS has

been performed with Ph PSe, following a reported

3

2

3

procedure. This reagent appears easier to handle than the

reported (phenylseleno)phosphonic dichloride in the presence

2

4

of pyridine. It was therefore used also for the selenation of

2

,2′-diselenosalicylic acid to aﬀord the COSeSe, albeit in

limited yield (10%). Note that the only mention of COSeSe

does not report its synthesis. The sulfuration of 2,2′-

diselenosalicylic acid with P S in dioxane gives CSSSe in

4

10

10,43

8

0% yield. This route diﬀers from that reported earlier where

shown in previous studies,

the electrophilic/nucleophilic

34

the already formed COSeSe was treated with P₄S₁₀in CS₂.₃

CSSeS was already reported and structurally characterized.

Only the thiocarbonyl diselenide CSSeSe is still unknown.

power of CD/CC sites can be monitored by the L/ρ value at

the corresponding sites (normalizing by ρ permits the

comparison between atoms with a diﬀerent number of

electrons). Thus, the larger the positive/negative L/ρ

magnitude, the more nucleophilic/electrophilic power of the

site.

5

2

.2. Computational Details and Topological Analyses

2

of ρ(r) and L(r) = −∇ ρ(r). Geometry optimizations,

frequency calculations, and topological investigations on (i)

optimized monomers, (ii) dimers extracted from the crystal

structures, and (iii) anionic ﬂuoride adducts were performed at

the B3LYP-D3/aug-cc-pVTZ level of theory. The electrostatic

potential (ESP) maps were plotted for the monomers on the

The methodology based on the topology and the

distribution of L(r) has proved to be very useful in describing

1

0,43−49

diﬀerent electrophilic−nucleophilic interactions.

Hence, using the L/ρ parameter, the quantity Δ(L/ρ) = (L/

ρ) − (L/ρ) aims to evaluate the CC···CD interaction.

0

.001 and 0.002 au electron density isosurfaces. The

CC

CD

C

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Accordingly, the larger the positive diﬀerence Δ(L/ρ) = (L/

ρ) − (L/ρ) is, the more important is the nucleophilic···

structures of the prepared compounds were determined from

single crystal X-ray diﬀraction. COSS crystallizes in the

CC

CD

10,43

electrophilic interaction.

To monitor the intensity of the

monoclinic system, space group P2 /c, with two molecules in

1

electrophilic···nucleophilic interaction, we introduce in this

the asymmetric unit (marked A and B in Figure 2a). Both

COSeS and COSeSe were found to be isostructural with

COSS [Figure S1 −S3 ]. Note that positional disorder observed

between carbonyl and S−Se bond in COSeS was solved with

the two positions in a 95:5 relative occupancy. For the

discussion on crystal packing and intermolecular interactions

in COSeS, we only utilized the major component of the

disorder. Analysis of crystal packing of these three crystal

structures reveals the formation of ····AABBAABB···· chains,

running along the a + b and a − b directions [Figure 2a;

Figures S1 −S3 ]. These chains are stabilized primarily by three

unique π···π stacking motifs (namely AA, AB, BB) with the

molecular centroid −centroid distances in the range of 3.6−3.9

Å [Figure 2a; Table S1 ]. The centroid−centroid distance tends

to increase from COSS to COSeSe molecules. While ····

AABBAABB···· chains are parallel along each a + b and a − b

direction, they are perpendicularly oriented in alternated way

along the c-axis [Figure 2a; Figures S1 −S3]. These π-stacking

molecular chains are assembled to each other by hydrogen

bonding (C−H···O, C−H···π, C−H···S, and/or C−H···Se)

and chalcogen bonding (Ch···Ch′; Ch = S, Se; Ch′ = O, S)

interactions (Table S2 ), thus generating the 3D network of the

crystal structure [Figures S1 −S3 ].

2

work the descriptor Δ(L/ρ)/d

= [(L/ρ)_C_C− (L/

CD···CC

2

ρ) ]/d

, where d

is the CD···CC distance. The

descriptor increases with the electrophilic and the nucleophilic

CD

CD···CC

power of the sites, and with shorter distances. Therefore, the

2

larger is the positive value of Δ(L/ρ)/d

the most

CD···CC

relevant is the interaction. A more detailed description on the

L (r ) function and its topology is provided in section S1 of the

Supporting Information.

2

.3. Geometrical Description of the Chalcogen Bond.

The relative orientation of two atoms involved in a chalcogen

bond (or any other noncovalent interaction) is very crucial to

understand the electrophilic−nucleophilic behavior of the

interaction. In the crystal structures discussed here, we observe

two cases of chalcogen bonding interactions, namely

+

−

+

−

3

sp

2

3

sp

Ch (δ )···Ch (δ ) and Ch (δ )···Ch (δ ). In Figure 1 ,

sp

The fourth carbonyl derivative, COSSe, crystallizes in the

monoclinic system, space group C2/c, with one molecule in the

asymmetric unit. It is isostructural with the two prepared

thiocarbonyl derivatives CSSS and CSSSe [Figures S4 −S6].

Note that the structure of CSSS has been already reported with

two diﬀerent polymorphs (CCDC codes: AYOZAR (space

Figure 1. Representation of ζ and ζ angles considered for (left)

1

2

3

2

3

Ch ···Ch and (right) Ch ···Ch chalcogen bonding interactions.

sp

Ch = chalcogen atom; X/X′/Y/Y′ = any atom.

50

51

ζ₁corresponds to angles with regard to the Ch-atom acting as

group C2/c) and AYOZAR01 (space group P2 /n)). The

1

electrophile (left side moiety: X−Ch ···Ch_r_i_g_t_h), whereas ζ₂

overall crystal packing of these three-isostructural crystal

structures COSSe, CSSS and CSSSe [Figure 2b; Figures

S4 −S6 ] is very similar to that observed for the previous set of

isostructural crystal structures (COSS, COSeS, and COSeSe).

Here, the molecular packing also consists of π-stacked

molecules forming chains interlinked to each other via

hydrogen and chalcogen bonding interactions. The diﬀerence

in the molecular packing of this set of molecules is primarily

because the molecule in the asymmetric unit forms π-stacking

molecular chains using two alternating and unique π-stacking

left

corresponds to angles with regard to the Ch-atom acting as

nucleophile (right side moiety: Ch ···Ch_r_i_g_h_t-Y). Interactions

left

3

2

between sp and sp hybridized chalcogen atoms are angularly

described by two ζ angles (ζ and ζ ) and one ζ angle

1

1A

1B

2

3

(

Figure 1, left), whereas for interactions involving two sp

hybridized chalcogen atoms, it results in two ζ angles (ζ and

1

1A

ζ ) and two ζ angles (ζ and ζ ) (Figure 1, right).

1

B

2

2A

2B

2

.4. Intermolecular Interactions and Crystal Packing.

2

.4.1. Overall Description of Crystal Structures. Crystal

Figure 2. Crystal packing of (a) COSS, (b) CSSS (AYOZAR), (c) CSSS polymorph (AYOZAR01), and (d) CSSeS (CCDC code: NABQUC),

showing the presence of π-stacking, hydrogen bonding (cyan), and chalcogen bonding (purple) interactions.

D

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Figure 3. ChB motifs in COSS (left) and COSeSe (right). Labels A and B in the suﬃx of atomic symbols point to the two molecules present in the

asymmetric unit.

a

Table 1. Structural Characteristics of the ChB Interactions in COSS and COSeSe.

compound

motif

I

interaction

σ-hole

d (Å)

RR

ζ₁(deg)

ζ₂(deg)

114.6

115.2

128.7/92.4

139.6/109.7

123.3/131.0

110.7/115.2

111.5

COSS

C7A/S2A−S3A···O1AC1A

R2

R1A

R1B

R2

3.081

3.199

3.701

3.837

3.830

3.984

3.125

3.292

3.596

3.819

3.769

3.925

0.93

0.96

1.00

1.04

1.03

1.08

0.91

0.96

0.95

1.00

0.99

1.03

165.1/74.0

162.7/67.8

165.1/77.1

90.4/148.6

162.1/78.9

160.7/0.6

160.8/72.7

155.8/64.9

78.5/165.8

88.5/147.1

159.8/76.2

157.7/68.8

C1A/S3A−S2A···O1AC1A

C1A/S3A−S2A···S3A−C7A/S2A

C7A/S2A−S3A···S3B−C7B/S2B

C7B/S2B−S3B···S2A−C1A/S3A

C1B/S3B−S2B···S2A−C1A/S3A

C7A/Se2A−Se3A···O1AC1A

C1A/Se3A−Se2A···O1AC1A

C1A/Se3A−Se2A···Se3A−C7A/Se2A

C7A/Se2A−Se3A···Se3B−C7B/Se2B

C7B/Se2B−Se3B···Se2A−C1A/Se3A

C1B/Se3B−Se2B···Se2A−C1A/Se3A

II

III

COSeSe

I

113.1

R1A

R1B

R2

125.5/93.4

143.1/103.1

128.3/130.6

110.9/112.9

II

III

R2

a

d corresponds to the intermolecular distance between the atoms participating in the chalcogen bond interaction. RR is the reduction ratio, deﬁned

as the ratio between the intermolecular distance (d) and the sum of van der Waals radii of interacting atoms. ζ and ζ angles are deﬁned in Figure

1

2

1.

motifs (Table S3), which results in the formation of ····

AAAAAAAA···· chains (Figure 2b), as opposed to ····

AABBAABB···· chains in the previous set of molecules formed

by two molecules (A and B) present in the asymmetric unit

original work. The main feature of this crystal structure

concerns the presence of two similar chains of π-stacking

molecules (Figure 2d), leading to ····AAAA···· and ····BBBB····

arrangements with very similar stacking distances (A···A =

4.100 Å, B···B = 4.100 Å). It is also interesting to note that

CSSeS presents the largest number of chalcogen bonding

interactions among all crystal structures analyzed in this study

(Figure S8; Table S6 ).

Overall, it appears that the crystal packing of these

chalcogen-rich aromatic molecules is primarily stabilized by

π-stacking motifs, complemented with diﬀerent hydrogen

bonding and chalcogen bonding interactions that act as linkers

for connecting the π-stacked molecular chains. With the aim of

exploring the speciﬁc anchoring sites associated with the Ch2−

Ch3 bond (S−S, S−Se, Se−Se), we will now focus exclusively

on the chalcogen bonding interactions present in these

structures.

2.4.2. Chalcogen Bonding Interactions. 2.4.2.1. Eﬀect of

Replacing Sulfur with Selenium in the Ch2−Ch3 Bond

(COSS vs COSeSe). There exist three unique motifs in both

COSS and COSeSe that can be described in terms of

chalcogen bonding interactions (Figure 3; Table 1). Motif I

consists of a double Ch2/Ch3···O interaction (Ch = S, Se)

bifurcated at O, which acts as a nucleophile, involving the R2

σ-hole region (see Scheme 1 for localization of R1A, R1B, and

R2 σ-hole regions). This motif is further supported by the

presence of an additional ChB interaction (Ch2···Ch3),

utilizing the R1A σ-hole region at Ch2. Hence, in motif I, in

addition to the previous bifurcated interaction at O, a further

(Figure 2a). In addition to the appearance of chalcogen

bonding interactions, the presence of a chalcogen-chalcogen

contact (involving Se at the Ch3 position; see Table S4)

similar to a type-I halogen−halogen interaction also shows in

the crystal structures of COSSe and CSSSe.

For comparison purposes, we also describe hereafter the

other crystal structures that, belonging to this series, were

previously reported in the literature. They concern the second

5

1

polymorph of CSSS and CSSeS. CSSS (AYOZAR01)

crystallizes in the monoclinic system, space group P2 /n,

1

with one molecule in the asymmetric unit. Only one unique π-

stacking motif (molecular centroid-centroid distance = 4.006

Å) is observed, which results in the formation of ····AAAAA····

molecular chains running along the a-axis (Figure 2c). Similar

π-stacked molecular chains are observed in a zigzag arrange-

ment down the c-axis with interconnectivity provided by

hydrogen and chalcogen bonding interactions [Figure 2c;

Table S5 ]. Down the b-axis, the interconnectivity between

closer parallel-arranged π-stacked chains is supported by

hydrogen bonding interactions (Figure S7; Table S5 ).

CSSeS crystallizes in the monoclinic system, space group

P2 /c, with two molecules (A and B) in the asymmetric unit

1

52

(

CCDC code: NABQUC). For the analysis of possible

hydrogen bonding interactions, we have added hydrogen

atoms at calculated positions as they were not reported in the

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double Ch3···O/Ch2 interaction shows bifurcated at Ch3,

both sharing the Ch3···O contact. The chalcogen atom present

at Ch3 position in two of the molecules is involved in the

formation of a Ch3···Ch3 chalcogen bond interaction via the

R1b σ-hole region (motif II in Figure 3). The Ch2 chalcogen

atom also acts as a nucleophile, resulting in a possible double

Ch2···Ch2/Ch3 chalcogen bonding motif (bifurcated at Ch2)

involving the R2 σ-hole region (motif III in Figure 3). The

intermolecular distance between the chalcogen atoms in some

of the possible chalcogen bonding interactions are large

aspect of this motif is that the magnitude of the ζ angle

2

(∠CS···S) ∼ 150° (Table 2) is much larger than expected

for a usual lone-pair position of the sulfur atom. This

chalcogen bonding network observed in CSSS AYOZAR

polymorph is found identical in isostructural COSSe and

CSSSe compounds (Figure S9; Table S7 ). On the other hand,

the only ChB motif in the AYOZAR01 polymorph of CSSS

(Figure 4 right) consists of a single interaction between the R2

σ-hole region with the lone pair of thiocarbonyl sulfur atom.

Finally, the crystal structure of CSSeS has a unique network

of chalcogen bonding interactions and is not isostructural with

any other crystal structure of the analyzed family (see Figure

S9 and Table S7 ).

In the summary of this section, it appears that despite their

closely related molecular structures, the solid-state organization

of these compounds can vary signiﬁcantly, particularly when

considering which one of the possible σ-holes around the

Ch2−Ch3 bond is actually engaged in a ChB interaction. On

the other hand, the analysis of the geometrical parameters of

the diﬀerent chalcogen bonds present in the crystal structures

shows that all three possible σ-hole regions are actually capable

to participate in the formation of chalcogen bonding

interactions, with the strongest ones involving the R2 σ-hole

region as observed from the structural RR parameter.

(

reduction ratio RR > 1, Table 1), based on the vdW distance

53

criteria. The existence, strength and directionality of these

bonding interactions will be further analyzed via the

topological analyses of ρ(r) and L(r) in subsequent sections.

Overall, it appears from the geometrical parameters (d, ζ , ζ in

1

2

Table 1) that all three possible σ-hole regions present around

the Ch2−Ch3 bond are participating in the formation of

directional chalcogen bonding interactions, the strongest ones

seeming to involve the R2 region from the structural RR

parameter. The chalcogen bonding network in COSeS (Figure

S9; Table S7 ) is similar to that of COSS and COSeSe due to

isostructurality.

2

.4.2.2. Eﬀect of Replacing Carbonyl with Thiocarbonyl

(

COSS vs CSSS). Replacing carbonyl with thio-carbonyl group

results in notable changes in chalcogen bonding interactions,

along with changes in molecular packing [cf. Figure 2, part a

and parts b and c]. In terms of ChB interactions, CSSS have

two unique motifs in the AYOZAR polymorph, while only one

appears in the AYOZAR01 polymorph (Figure 4 ; Table 2 ).

2

.5. Regions and Anchoring Sites for Molecular

Assembly and Reactivity around the Ch2−Ch3 Bond

in Monomers. In the following, we will ﬁrst perform a

thorough theoretical investigation of the electrostatic potential

2

and the topological features of ρ(r) and L(r) = −∇ ρ(r),

particularly around the dichalcogenide bond of individual

molecules. This initial step will permit to determine the

location of the most electrophilic chalcogen atoms within these

series, as well as to give a rationale for understanding molecular

assembly in the solid state and chemical reactivity.

2.5.1. Electrostatic Potential Maps. The presence of a σ-

hole is often associated with the presence of a positive

54

electrostatic potential region around the chalcogen atom.

Accordingly, DFT calculations of the electrostatic potential

(ESP) have been performed for the eight compounds

investigated in this study. For a better visualization of positive

ESP regions around the Ch2−Ch3 dichalcogenide bond, maps

have been drawn on the molecular ρ = 0.002 au isosurface

Figure 4. ChB motifs in AYOZAR (left) and AYOZAR01 (right)

polymorphs of CSSS. The atomic labels used in this ﬁgure are

diﬀerent from the ones reported in the literature in order to be

consistent with these across the molecules discussed in the

manuscript.

(

Figure 5 and Figure S10 ). For comparison, ESP calculations

mapped on the molecular ρ = 0.001 au isosurface are gathered

in Figures S11 and S12 .

In region R1A, a relatively low magnitude of positive ESP is

observed for the four compounds, with small larger magnitudes

for selenium derivatives as compared to sulfur ones (Figure 5).

The positive magnitude of ESP decreases when the

Motif I in AYOZAR is actually similar to motif I observed in

the crystal structure of COSS (and therefore also in the

isostructural COSeSe) as it involves both regions R1A and R2

as ChB donors. Motif II in AYOZAR utilizes the R1B region in

the formation of a chalcogen bonding interaction. The unique

Table 2. Structural Characteristics of the ChB Interactions in Both Polymorphs of CSSS (CCDC Codes: AYOZAR and

a

AYOZAR01).

compound

motif

I

interaction

σ-hole

d (Å)

RR

ζ₁(deg)

ζ₂(deg)

CSSS (AYOZAR)

C7/S2−S3···S1C1

C1/S3−S2···S1C1

C1/S3−S2···S3−C7/S2

C7/S2S3···S1C1

R2

R1A

R1B

R2

3.428

3.376

3.955

3.373

3.555

3.503

0.95

0.94

1.10

0.94

0.99

0.97

164.1/71.0

170.7/73.7

86.6/164.4

100.2/151.2

163.1/71.6

167.4/74.4

107.1

98.7

128.5/76.6

153.7

127.8

95.9

II

I

CSSS (AYOZAR01)

C7/S2−S3···S1C1

C1/S3−S2···S1C1

R2

a

d corresponds to the distance between the atoms participating in the chalcogen bond interaction. RR is the reduction ratio, deﬁned as the ratio

between the intermolecular distance (d) and the sum of van der Waals radii of interacting atoms. ζ and ζ angles are deﬁned in Figure 1.

1

2

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Figure 5. ESP maps of COSS, COSeSe, CSSS, and CSSeSe drawn along R1A, R1B, and R2A σ-hole regions. ESP is mapped on the molecular ρ =

.002 au isosurface. Blue: positive. Red: negative. ESP values in the ﬁgure are reported in kcal/mol. See Figure S10 for other compounds.

0

a

Table 3. Topological Parameters of the Covalent Bonds Bearing Chalcogen Atoms in COSS, COSeSe, CSSS, and CSSeSe

COSS

COSeSe

CSSS

CSSeSe

2

ρ

∇ ρ

|V|/G

ρ

∇ ρ

|V|/G

ρ

∇ ρ

|V|/G

ρ

∇ ρ

|V|/G

Ch2−Ch3

Ch2−C1

Ch3−C7

Ch1−C1

0.95

1.20

1.35

2.89

−2.65

−5.48

−8.32

−7.54

2.60

3.04

3.40

2.11

0.68

0.96

1.07

2.90

−0.82

−2.53

−3.39

−6.15

2.26

2.53

2.56

2.09

0.93

1.38

1.36

1.53

−2.45

−8.28

−8.51

−4.77

2.56

3.30

3.42

2.21

0.67

1.09

1.07

1.54

−0.72

−3.47

−3.48

−5.18

2.23

2.55

2.57

2.23

a

3

2

5

ρ is in e/Å , ∇ ρ is in e/Å , and |V|/G is dimensionless. See Tables S8 and S9 for other compounds and bonds

thiocarbonyl group replaces the carbonyl group. The low

magnitude of positive ESP in this region is due to the negative

contribution of neighboring CO/CS groups. This trend

can inﬂuence the σ-holes associated with chalcogen atoms,

which can be signiﬁcantly aﬀected by neighboring atoms in the

region of interest (namely, around the Ch2−Ch3 bond in our

study). Accordingly, whereas we have already established the

involvement of the R1A σ-hole region in chalcogen bonding

formation (see the crystal structures described above), the ESP

maps can be unable to disclose the true electrophilic character

of the chalcogen atom along this R1A σ-hole region.

The positive magnitude of ESP in region R1B is found

considerably higher than that observed in region R1A. Here,

the ESP distribution is however signiﬁcantly inﬂuenced by the

positive contribution coming from the acidic hydrogen atom in

the close vicinity, making diﬃcult to assess the actual

contribution of the chalcogen atom to the observed position

and magnitude of the ESP maxima.

In region R2, while two σ-holes could be considered (each

along the prolongation of one of the two C−Ch bonds), only

one positive ESP extremum appears. It shows close to the

center of Ch2−Ch3 bond and results from the merged

contribution of both chalcogen atoms. As a consequence, the

magnitude of the positive ESP in this region is high, clearly

establishing the presence of a unique σ-hole region caused by

two contributions. This feature well corroborates with the

formation of a short and directional chalcogen bonding

interaction via this region. In addition, it is pointed out that

the ESP magnitude in the R2 region is higher for molecules

with the thiocarbonyl group than for those bearing the

carbonyl group, and for those bearing Se instead of S at Ch2

and Ch3 positions.

2.5.2. Topology of ρ(r). From the above ESP analysis, it is

diﬃcult to obtain an accurate description permitting to

understand the electrophilic behavior of the chalcogen atoms

in these molecules. Experimental and theoretical studies have

clearly established that nucleophile attack on the chalcogen

atoms Ch2 and Ch3 is possible along all the three possible σ-

16,55−61

hole regions.

It is also well documented that the

dichalcogenide Ch2−Ch3 bond is often considered as the

weakest one within this family of molecules and is highly

16,55−61

susceptible to follow up a nucleophilic attack.

In

comparison to other covalent bonds in such 1,2-dichalcoge-

noles, the weak nature of Ch2−Ch3 can be established by

QTAIM calculations performed on the optimized molecules in

gas-phase. Indeed, as gathered in Table 3, which focuses on all

the covalent bonds where chalcogen atoms are involved (for

the rest of the bonds and molecules see Tables S8 and S9 ), the

2

Ch2−Ch3 bond exhibits the lowest magnitudes of ρ and ∇ ρ

2

at BCP’s. For Ch2−Ch3, while |V|/G > 2 and ∇ ρ < 0 establish

unambiguously the covalent nature of the bond, its |V|/G value

is smaller than those observed for other bonds present in the

molecules, except for CCh1 (CO, CS) that also

2

possess a more negative ∇ ρ magnitude and therefore a higher

concentration of charge. The relatively low magnitude of |V|/G

for CO and CS can be attributed to the nature of these

bonds that are highly polarized. The topological parameters of

the S−S bond in COSS are similar to those observed in CSSS.

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Table 4. Integrated Charges (in e) on Selected Atoms Involved in Chalcogen Bonds

COSS

COSSe

COSeS

COSeSe

CSSS

CSSSe

CSSeS

CSSeSe

Ch1

Ch2

Ch3

−1.13

0.02

0.08

0.96

−0.16

−1.13

−0.08

0.28

0.96

−0.24

−1.13

0.20

−0.03

0.90

−1.13

0.09

0.17

0.90

−0.23

0.14

0.15

0.08

−0.46

−0.16

0.14

0.05

0.27

−0.45

−0.24

0.16

0.35

−0.04

−0.55

−0.15

0.16

0.24

0.16

−0.55

−0.24

(

Ch1)C1

(

Ch3−)C7

−0.15

Likewise, the topological parameters of the Se−Se bond in

COSeSe are similar to those observed in CSSeSe. This

suggests that replacing CO by CS does not signiﬁcantly

aﬀect the electronic characteristics of the Ch2−Ch3 bond. In

comparison, as expected, replacing sulfur by selenium (COSS

vs. COSeSe and CSSS vs. CSSeSe) leads to a notable

weakening of the dichalcogenide bond, as shown by the

2

recurrent lower magnitudes of ρ, ∇ ρ, and |V|/G obtained for

the Se−Se bond (Table 3).

To further analyze the characteristics of the chalcogen

atoms, their net charges have been computed by integration

38

within their atomic basins and are collected in Table 4 for

the eight compounds (see Table S10 for all atoms). The net

charge of Ch3 remains unaﬀected when comparing a carbonyl-

containing molecule with its thiocarbonyl counterpart. On the

other hand, Ch2 becomes more positively charged from CO

to CS derivatives (Table 4). The reason is brought close to

the fact that, in the case of thiocarbonyl derivatives, the lone

pairs of Ch2 are delocalized over the C1−Ch1 and C1−Ch2

bonds, resulting in a decrease of the electron population

belonging to Ch2. This behavior is supported by the

topological parameters associated with C1−Ch2 bonds

(

Table 3). Indeed, the C1−Ch2 bond is stronger in case of

thiocarbonyl derivatives (larger magnitudes of ρ and |V|/G,

and more negative ∇ ρ value) as compared to its carbonyl-

2

containing counterpart. The net charge of atoms also reveals

that the polarization of CCh1 changes, depending on the

chalcogen atom. Thus, while the CO bond exhibits the

2

5

Figure 6. Left: L(r) = −∇ ρ(r) maps [e/Å , contours are in

logarithmic scale: positive (red) and negative (blue)] for COSS (top)

+

−

expected δ ···δ character, the CS bond shows surprisingly

−

+

2

the opposite δ ···δ polarization, further supporting the

delocalization of Ch2 lone pairs in the case of CS. The

larger net positive charge found for Ch2 is also consistent with

the results obtained from the ESP analysis (Figure 5), which

shows a larger positive ESP magnitude in region R2 for

molecules bearing CS instead of CO. In carbonyl

derivatives (Ch1 = O), the very high positive charge found

for C1 might explain the speciﬁc reactivity of these compounds

and COSeSe (bottom). Right: The ∇ ρ(r) = 0 maps are plotted for

COSS (top) and COSeSe (bottom) with atomic portioning. Relevant

CPs of L(r) in the valence shell of chalcogen atoms are denoted in

maps as spheres [(3,−1) CPs are green, (3,+1) CPs are pink, and (3,

+

3) CPs are violet]. (3,−3) CPs corresponding to lone pairs of Ch2

and Ch3 are out of plane in the left (they are shown in Figure S13),

2

and they are hidden by the enclosing surfaces ∇ ρ(r) = 0 in the right.

See Figures S14 −S16 for other compounds.

16

toward nucleophiles, leading to C1−Ch2 bond scission. The

28,29

same reactivity is also observed for CSSS,

but probably for

2

3

with hybridized geometries at Ch1 , Ch2 , and Ch3

sp

a diﬀerent reason as it is actually the Ch2 chalcogen atom that

positions, in the molecular plane for Ch1, and in the planes

bisecting the C−Ch2−Ch3 and C−Ch3−Ch2 angles for Ch2

and Ch3, where the lone pairs of Ch1, Ch2, and Ch3 stand

(Figure S13; Tables S11 −12). As expected, the nucleophilic

power follows the trend O > S > Se (Table S11). The

nucleophilic power of CC sites is slightly lower at Ch2 than at

Ch3 for molecules with Ch2 = Ch3 (for example, in COSS, L/

ρ = 9.2 and 9.7 Å respectively). These CPs are important

because the location of other observed CPs are actually

dictated by the location of dominant (3,−3) CPs. The

potential electrophilic charge depletion (CD) sites should lie

close to the molecular plane around the Ch2−Ch3 bond, and a

careful look in type and position of corresponding CPs should

be taken (Figure 6 and Figures S14 −S16). As shown in Figure

6, the valence shell charge concentration (VSCC) of S-atoms

bears the highest positive charge.

2

.5.3. Topology of L(r) = −∇ ρ(r). In order to further assess

the electrophilic power of chalcogen atoms in the series, we

have also analyzed the L(r) function around the Ch2−Ch3

covalent bond (Figure 6 and Figures S13 −S16). Previous

studies on halogen and chalcogen bonding have clearly

demonstrated the usefulness of L(r) in describing the

nucleophilic and electrophilic regions in the valence-shell of

−

2

10,43

this kind of atoms.

In atomic basins, even when only the

external valence-shell is considered, a large number of CPs

derived from L(r) are observed. For chalcogen atoms (Ch1,

Ch2, and Ch3), nucleophilic charge concentration (CC) sites

are well identiﬁed in their lone-pairs regions as (3,−3) CPs

(Figure S13 ). These (3,−3) CPs (CC sites) appear by pairs

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−

2

Table 5. Electrophilic Power (L/ρ in Å ) of Charge Depletion (CD) Sites in the Electron Valence Shell of Chalcogen Atoms

a

in Gas Phase

COSS

COSeSe

CSSS

CSSeSe

2

Type

∇ ρ

ρ

L/ρ

∇ ρ

ρ

L/ρ

∇ ρ

ρ

L/ρ

∇ ρ

ρ

L/ρ

CP1a

CP1b

CP2a

CP2b

CP3a

CP3b

CP3c

CP3d

CP3e

CP 3f

CP4a

CP4b

CP4c

(3,+1)

(3,−1)

(3,+1)

(3,+3)

(3,+1)

(3,+3)

0.01

0.25

0.80

0.88

0.86

1.16

1.15

0.33

0.32

0.34

0.33

0.37

0.38

−0.01

−0.31

2.11

1.57

7.48

2.69

2.68

0.34

0.36

−7.92

−7.44

0.78

−0.03

−1.34

−1.60

−9.27

−8.26

1.65

1.64

1.67

2.41

0.78

0.82

0.86

0.87

1.19

1.15

0.33

0.32

0.34

0.33

0.37

0.38

0.37

−1.00

0.04

1.56

1.84

7.79

3.02

2.67

0.39

0.36

−7.74

−6.58

−1.86

−1.35

−8.68

−8.29

1.66

1.65

1.66

1.63

2.40

1.38

1.47

1.58

0.59

0.57

0.36

0.37

−2.39

−2.58

−4.39

−4.27

1.29

1.45

1.55

1.56

0.62

0.57

0.35

0.36

−2.08

−2.54

−4.33

7.21

7.18

−5.03

−5.16

−4.88

−4.93

−6.49

−6.45

−6.63

−5.00

−5.12

−4.91

−5.06

−6.51

−6.71

−6.73

1.56

0.29

−5.38

1.55

0.29

−5.34

2.45

2.52

2.55

2.49

a

2

3

5

ρ and ∇ ρ are in e/Å and e/Å units. See Table S14 for other compounds.

around the S−S bond in COSS (and similarly in CSSS, Figure

S14 ) reveals the presence of two (3,+1) CPs in the topology of

L(r) (marked as CP1a and CP1b) in the region around the

extension of the S−S bond. In COSS, CP1a and CP1b are

present with ∠Ch3−Ch2−CP1a and ∠Ch2 −Ch3 −CP1b

angles of 154.7° and 152.4°, respectively (Table S13). Two

additional (3,+1) CPs (marked as CP2a and CP2b) are also

present with ∠C1−Ch2−CP2a and ∠C7−Ch3−CP2b angles

of 149.0° and 151.8 ° roughly along the two single C−S bonds

of the molecule (Table S13). In addition, the VSCC region

also reveals the presence of two (3,−1) CPs (marked as CP3a

and CP3b) that are placed in the planes where lone pairs stand,

bisecting the ∠C−S−S angles. Therefore, each sulfur atom in

COSS (and in the other molecules) is associated with three

unique CPs (two (3,+1) and one (3,−1)) laying in the

molecular plane within the VSCC region (Figure 6, Figures

S14 −S16). This trend is fully consistent with the topology of

R1B. Finally, in the outer VSCD region of sulfur atoms another

(3,+1) and (3,+3) CPs exhibit (namely, CP3c-f). They are

placed in the molecular plane, and close to the planes bisecting

the ∠C−S−S angles that contain the lone pairs of sulfur atoms.

Consequently, although they are standing in regions with

relevant electrophilic power (see their L/ρ values), they are

less able to perform as anchoring sites for molecular

assemblies, as eventual nucleophilic centers will feel the

repulsion exerted by the lone pairs that are in close vicinity.

2

Furthermore, as CP4a−c sites, they are also out of the ∇ ρ(r)

= 0 isosurface, which is closed in this region and avoids the

nucleophilic attack for reactivity purposes.

The descriptor L/ρ (Table 5 and Table S14 ) was computed

in order to evaluate the electrophilic power of these sites. The

lower is L/ρ the more important is the electrophilic power,

because the electron distribution per charge density unit is

more depleted. Whereas (3,+3) and (3,+1) CPs exhibit

negative (or low positive) L/ρ magnitudes, (3,−1) CPs show

large positive ones, clearly pointing the former as more eﬃcient

electrophilic sites. Around the S−S bond in COSS, the (3,+3)

and (3,+1) CPs characteristic of regions R1a, R1b, and R2

(namely, CP1a, CP1b, and CP4a−c) exhibit the highest

10

L(r) previously described for the sulfur atom. The iso-surface

2

∇

ρ(r) = 0 around the sulfur atoms (Figure 6, top-right)

shows holes in regions R1A and R1B, where the critical points

CP1a and CP1b are sitting partially visible in the 3D map. In

contrast, other CPs are not visible, hidden by the iso-surface.

The cavities around the R1A and R1B regions indicate that a

potential nucleophilic attack will be more favorable along the

S−S bond than along the C−S bonds (region R2). In region

R2, it is however noteworthy the existence of another (3,+1)

−

2

electrophilic power −6.6 < L/ρ < 0 Å . It should be noted

that, in spite of their topological features, CP2a−b and CP3a−

b sites of S-atoms should be considered as bad electrophilic

sites, as they show large L/ρ > 0. They are however included in

Table 5 for comparison purposes with the rest of CD sites.

For the corresponding diselenide COSeSe, all CPs are

present in the outer valence shell charge depletion (VSCD)

region, because the valence shell of the atom is fully depleted

2

CP (CP4a) placed out of the iso-surface ∇ ρ(r) = 0 (in the

atomic valence shell charge depletion region, VSCD), facing

the S−S BCP. Figure 6 and the angular values ∠C1−Ch2−

CP4a = 129.9° and ∠C7−Ch3−CP4a = 127.1° (similar to

each other) clearly indicate that CP4a is very close to the

interatomic Ch2−Ch3 surface, rather than along to the

extension of C−Ch bonds. The emergence of this (3,+1) CP

is the consequence of two (3,+3) CPs (CP4b and CP4c) in the

closer neighborhood, making the region where the three CPs

stand of signiﬁcant electrophilic nature. As for CP1a (region

R1A) and CP1b (region R1B), CP4a (region R2) also stands

in the region of the expected σ-hole, as observed in the

electrostatic potential maps (Figure 5). Hence, although the

nucleophilic attack is more diﬃcult through region R2 in the

2

(∇ ρ(r) > 0) due to the screening made by the large quantity

of core electrons in selenium atoms (Figure 5 bottom and

Figures S14 −S16 ). Around the Se−Se bond in COSeSe, and

compared with the S−S bond in COSS, only (3,+1) CPs at

CP1a, CP1b, CP3c, CP3d, and CP4a sites and (3,−1) CPs at

CP3a and CP3b sites appear, the other CPs observed with S-

atoms being merged by coalescence into one of the observed

CPs in the same region with Se atoms. The positions of CP1a/

CP1b sites around selenium atoms are quite diﬀerent with

respect to these found around sulfur atoms. Indeed, while in

COSeSe the angles ∠Ch3 −Ch2 −CP1a and ∠Ch2−Ch3−

CP1b are both 129° (Table S13), in COSS they show at

∼150°. Accordingly, CP1a and CP1b are found well into the

2

absence of a hole in the iso-surface ∇ ρ(r) = 0, an electrostatic

interaction can take place with the intermolecular environment

involving this favorable electrophilic region, similar to R1A and

I

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Figure 7. Intermolecular bond critical points (BCPs, small green spheres), intermolecular bond paths (dashed lines), and charge concentration and

charge depletion (CC/CD) sites (yellow/pink/violet spheres) involved in the chalcogen bonding interactions present in motifs I, II, and III of

COSS, as well as a hydrogen bonding interaction in motif II. CPs of L(r) are (3,−3) in yellow, (3,+1) in pink, and (3,+3) in violet. Most relevant

CD/CC sites are indicated in bold in Table 6 and show close to the molecular planes represented in the ﬁgures.

basins of sulfur atoms in the disulﬁde, whereas in the diselenide

they are close to the interatomic surfaces between carbon and

selenium atoms, facing the C−Se BCPs (Figure 6). Hence, due

to steric hindrance, CP1a and CP1b sites in selenium atoms

can be less able to generate directional intermolecular motifs

along internuclear directions (low angle between CD···CC and

internuclear directions) in the assembly of molecules. On the

other hand, concomitantly to the shifting of CP1A and CP1b

CP3c and CP3d (see Table 5). However, as for CP1a/CP1b,

CP4a shows close to the interatomic surface Se−Se and the

corresponding BCP, where ρ(r) is locally concentrated

2

(∇ ρ(r) < 0). This makes more diﬃcult a nucleophilic attack,

even if this site can play a signiﬁcant role in the molecular

assembly, as steric hindrance does not take place as for CP1a/

CP1b. As expected, the electrophilic power associated with CD

−

2

sites around selenium atoms (−7.9 < L/ρ < − 2.4 Å ) is in

sites with respect to sulfur atoms, the selenium lone pairs (lp’s)

general larger than with those of sulfur atoms (−6.9 < L/ρ < 0

−

2

3

open their disposition (angles 144.8° < CC −Se −CC

<

Å ), even if for CP3c−d and CP4a slightly more negative

values are found for S-atoms (Table 5).

lp1

sp

lp2

3

1

50 °, 127.1° < CC −S −CC < 134.5° for all molecules)

Table S12), as previously observed with sulfur and selenium

lp1

sp

lp2

(

Very similar trends to those found for CD sites belonging to

S-atoms in COSS and to Se-atoms in COSeSe, are also

observed for the same atoms in the other molecules of the

same series (Figures S14 −16 and Table S14). Indeed, the

same CP types are closely placed in the same region of each

atom type (S or Se) from one derivative to another, while the

corresponding L/ρ values only vary in minor way. In addition,

it is noteworthy that the pairs of (3,+1) CPs (CP1a/CP1b and

CP3c/CP3f), as well as the pair of (3,−1) and (3,+3) CPs

(CP3a and CP3e) observed in COSS, were formerly identiﬁed

in the valence-shell of the S-atom in the sulfur derivative of a

series of chalcogenophtalic molecules (C O H Chal; Chal =

10

chalcogenophtalic derivatives. This electronic feature permits

an easier approach of nucleophiles along the direction bisecting

the ∠C−Se−Se angles than along that of ∠C−S−S angles.

CP3c and CP3d rank better than CP3a and CP3b in terms of

preferred electrophilic sites in their respective regions, as

shown by the more negative L/ρ values for the former (Table

5

). This trend follows the general consideration that the

electrophilic power of (3,+1) CPs is more important than that

of (3,−1) CPs because ρ(r) is depleted along two main

directions for the former and along only one for the latter. As

in the case of the S−S bond in COSS, an additional (3,+1) CP

is here observed close to the center of the Se−Se bond

8

2

4

10

O, S, Se, Te). In both families of molecules CPs are sitting at

very similar positions. In what it concerns the Se-atom, the

selenophtalic derivative showed the same pairs of CPs than

those found around the S-atom in the thiophtalic derivative,

(

1

marked as CP4a), showing angles of ∠C1−Ch2−CP4a =

24.1° and ∠C7−Ch3−CP4a = 122.1° and with a signiﬁcant

electrophilic power that is even larger than this observed for

J

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Figure 8. Intermolecular bond critical points (BCPs, small green spheres), intermolecular bond paths (dashed lines), and charge concentration and

charge depletion (CC/CD) sites (yellow/pink/violet spheres) involved in the chalcogen bonding interactions present in motifs I, II, and III of

COSeSe, as well as a hydrogen bonding interaction in motif II. CPs of L(r) are (3,−3) in yellow, (3,+1) in pink, and (3,+3) in violet.

whereas in the actual series the merge of sites by coalescence of

CPs lead to a single CP per pair. For S- and Se-atoms, the

observed L/ρ values in the corresponding CPs are more

negative for CP1a/CP1b in the actual series than in the

along the Ch2−Ch3 bond, whereas their positions in Se-atoms

made them less well placed due to their proximity to the basin

of the carbon atom, which can lead to steric hindrance. On the

other hand, for both S- and Se-atoms, CD sites in region R2

(mainly CP4 sites) stand for a side-on intermolecular

interaction of the Ch2−Ch3 bond with a nucleophile. For all

derivatives in this study, as determined from the L/ρ values,

the electrophilic power of CD sites in regions R1A and R1B of

Se-atoms is signiﬁcantly stronger than that around S-atoms,

whereas in region R2 it is slightly stronger around S-atoms.

2.6. Anchoring Sites around the Ch2−Ch3 Bond for

Molecular Assemblies. Following the above description of

the electron density distribution in isolated molecules,

particularly around the dichalcogenide bond, we now

concentrate on its consequences on the organization of the

molecules in space, with particular emphasis on the chalcogen

bonding interactions identiﬁed in the crystal structures. For

this purpose, we have carried out single-point calculations on

dimers (and a trimer) extracted from the crystal structures.

2.6.1. Topology of ρ(r). The involvement of all three

possible σ-hole regions in the formation of chalcogen bonds

(ChB) is indeed supported by the existence of bond critical

points (BCPs) between the interacting atoms of neighboring

molecules in the focused motifs (Figures 7, 8, and S17 −S23).

BCPs were also observed for several (not all) of the ChB

interactions with intermolecular distances well beyond the sum

of the vdW radii. The magnitude of ρ at BCP ranges from

−

2

chalcogenophtalic derivatives (by ∼−1 to −2 Å ), remaining

closely similar for the rest of CPs from one family to the other.

Hence, whereas under the inﬂuence of a diﬀerent intra-

molecular environment the topological features in the valence

shell of atoms are globally conserved, the particular electronic

properties found in the close neighborhood can modify in

some measure their characteristics. With this respect, it should

be also noted the diﬀerent level of calculations (MP2 vs

B3LYP) and basis sets used with each family of molecules.

Consequently, the merged CPs found for selenium and the

more powerful electrophilic sites found for both S- and Se-

atoms at CP1a/CP1b sites are brought close to the increased

electrophilic power of chalcogen atoms when they are

embedded in Ch−Ch bonds.

Overall, the topological analysis of L(r), pointing the

relevant atomic sites on the electrophilic regions associated

with the Ch2−Ch3 bond, gives a much more descriptive

information than ESP maps. It conﬁrms for example that CD

sites prone to drive a potential nucleophilic attack on disulﬁdes

will be more favorable along the S−S bond in regions R1A and

2

R1B, where the reactivity surface (∇ ρ(r) = 0) exhibits a hole.

2

For Se atoms, the contracted ∇ ρ(r) = 0 isosurface in their

valence shell indicates large accessible regions for nucleophilic

attack in regions R1a and R1b. In molecular assemblies

involving S-atoms, the pair of CD sites CP1a/CP1b show

accessiblity in regions R1A/R1B for CD···CC interactions

3

0.029 to 0.082 e/Å (Table 6 and Table S15). All the

interactions are of pure closed-shell interaction type with low

2

positive values of ∇ ρ and |V|/G < 1. The magnitudes of ρ and

K

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L

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M

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²ρ at BCPs are larger for Ch···O interactions (Ch = S or Se)

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∇

close vicinity, which usually show larger (L/ρ)_C_Dvalues and

signiﬁcantly lower α and d_C_C_·_·_·_C_Dmagnitudes (in Table 6; see,

for instance, the contributions of CP3d and CP4a sites in the

Se2A···O1A and Se2B···Se2A interactions of COSeSe). With

the aim to analyze the intensity of the electrophilic···

than for the other chalcogen bonding interactions present in

the motifs. This feature can be attributed to the more

important nucleophilic power of oxygen compared to other

10

chalcogen atoms (see (L/ρ)_C_Cvalues in Table S11). It is

important to note that BCPs are not observed for some

contacts in motifs with multiple chalcogen bonding (ChB)

interactions. These ChBs are mainly those showing a large

reduction ratio value (RR > 1; see Table 6) and/or less linear

chalcogen bonding interactions. For comparison, we have also

determined the topological parameters for the trimer

assembled by ChB interactions in COSS (see Figure 3) at

the same level of theory. Compared to the dimers embedded in

the trimer, a decrease is observed for the |V|/G ratio of ChBs in

motif III (bonding interactions with large intermolecular

distances), whereas no signiﬁcant variation is observed for the

nucleophilic interaction with a unique descriptor, we introduce

2

the magnitude Δ(L/ρ)/d

= [(L/ρ)_C_C− (L/ρ) ]/

CC···CD

CD

2

d

(see section 2.2), which increases with the electro-

CC···CD

philic and the nucleophilic power of the sites and with shorter

distances, and permits one to identify most relevant

interactions. Therefore, the larger is the positive value of

2

Δ(L/ρ)/d

the larger is the intensity of the interaction

CC···CD

0.09 Å < Δ(L/ρ)/d

−

4

2

−4

(

< 7.47 Å for the CC···CD

CC···CD

interactions in this work, excluding three negative values). This

is particularly interesting to focus on relevant CC···CD

interactions when several of them are occurring simultaneously

in a region of the intermolecular space. Hence, the descriptor

has been used to select relevant interactions in Table 6 and in

Figures 7 and 8 (for the rest of the interactions, see Table S15

and Figures S17−S23 in Supporting Information).

2

magnitudes of ρ , ∇ ρ, and |V|/G in the rest of the motifs

(

Table 6; Figure S23 ).

2

.6.2. Topology of L(r) = −∇ ρ(r). In the intermolecular

regions where ChB appears, the position of CP’s derived from

the L(r) function indicates that local nucleophilic···electro-

philic interactions take place via a face-to-face orientation of a

It is important to point out that the electrophilic region

where CP4a−c sites show, rises as the simultaneous

contribution of both chalcogen atoms. Consequently, for

calculating the α-angle magnitude that involves these CD sites,

the reference point is neither the Ch2 nor the Ch3 nuclear

coordinate but the Ch2−Ch3 BCP. Similarly, in the case of

selenium atoms, CP1a and CP1b sites are observed very close

to the C−Se interatomic surface, shifting their positions

toward the corresponding BCP. Hence, as for CP4a−c in

Ch2−Ch3, the α-angle corresponding to CP1a and CP1b sites

of Se-atoms is calculated taking the BCP as reference point

instead of the Se-nuclear coordinate. This choice is in line with

the previous ESP observations, where the local maxima of the

electrophilic regions R1A, R1B, and R2 emerged shifted

toward the middle of C−Ch2, C−Ch3, and Ch2−Ch3 bonds.

Consistent with previous studies, the Se···O chalcogen

bonding interaction exhibits the largest electrophilic···nucleo-

philic intensity, followed by the S···O interaction, as described

from their Δ(L/ρ)/d

out that these strongest electrostatically driven Se···O and S···

O interactions involve the σ-hole in region R2 because of its

signiﬁcant electrophilic character, while it is sterically more

favorable for the nucleophile (namely, the carbonyl oxygen) to

interact through this region.

(

3,−3) CP acting as a CC site and a (3,+1) CP (or a (3,+3)

CP in few cases) acting as a CD site (Figures 7−8; Figures

S17 −S23). This trend follows the general consideration that

(

3,−1) CPs cannot compete with (3,+1) CPs if they are

present in adjacent positions, because of the more powerful

electrophilic character of the latter. When several (3,+1) CPs

appear in the same region, it is likely expected that all of them

will be involved in the interaction with the nucleophilic center.

For sulfur, CP1a/CP3c along region R1A, CP1b/CP3d along

region R1B, and CP2a−b/CP4a−c/CP3c−d in region R2

emerge as possible CD sites involved as electrophiles. For

selenium, CP1a/CP3c along region R1A, CP1b/CP3d along

region R1B, and CP4a/CP3c−d in regions R2 emerge as the

possible CD sites involved as electrophiles. In all of the

interactions, (3,−3) CPs were involved as nucleophilic sites.

The local electrostatic intensity of the electrophilic···

nucleophilic interactions was evaluated using the normalized

quantity Δ(L/ρ) = (L/ρ) − (L/ρ) , its magnitude varying

2

magnitudes. It should be pointed

CD···CC

CC

CD

−

2

in the range 1.1 < Δ(L/ρ) < 23.9 Å for all the reported CC···

CD interactions in the crystal structures (excluding three

negative Δ(L/ρ) values in COSeS and CSSeS; see Table S15).

From Table 6, larger Δ(L/ρ) magnitudes correspond to

shorter d ···d

distances, indicating that more powerful

CC

CD

2.7. Molecular Reactivity in Fluoride Adducts. In

electrophilic···nucleophilic interactions lead to shorter CC···

CD geometries, and therefore to stronger driving forces in the

assembling of molecules. Strikingly, the angle α between CC···

CD and Ch···Ch′ (Ch = S, Se; Ch′ = O, S) directions is less

than ∼15° for stronger electrophilic···nucleophilic interactions

crystal structures, the way electrophilic−nucleophilic inter-

actions establish can depend on several aspects, such as steric

hindrance, presence of other interactions and overall crystal

packing. Therefore, it is diﬃcult to extrapolate the reactivity

behavior of this family of molecules based on crystalline

features only. In order to understand the chemical reactivity

around the Ch2−Ch3 bond in such dichalcogenides toward

nucleophilic attack, we devised a strategy where we used the

ﬂuoride anion as a probe. Accordingly, we optimized the

geometry of the eight compounds with one F anion sitting

around the Ch2−Ch3 bond in regions R1A, R1B, and R2,

using the same optimization criteria as used for monomers.

The small size of F allows for minimum steric hindrance,

while its anionic character results in a substantial nucleophilic

capacity.

−

2

(

Δ(L/ρ) > ∼5 Å ; see Tables 6 and S15 ), which also

corresponds to shorter CC···CD distances (d < ∼2.7 Å).

As reported in previous studies,

CC···CD

10,43

low magnitudes of α

(

<∼15°) point to local electrostatic electrophilic···nucleophilic

(

CD···CC) interactions that are at the origin of geometrical

−

preferences in molecular assemblies, as a consequence of their

ability to impose the relative orientation of interatomic

interactions (Ch···Ch′ in this work). Note that lesser

performing CD sites show larger α-angles (>∼20°) and

−

d

distances (>∼2.9 Å), in spite to exhibit sometimes

CC···CD

non-negligible (L/ρ) values (see, for instance, CP3d sites in

CD

Table 6). Consequently, they will lead to weaker electro-

philic···nucleophilic interactions than other CD sites in the

2.7.1. Geometry Optimization. Optimization of each

molecule with F results in three unique true minima, each

−

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laying in one of the focused regions, namely R1A, R1B, and R2

2.7.2. Stability of the Complexes. Twenty-four gas-phase

adducts were calculated at optimized geometries. The energies

of the adducts where the ﬂuoride anion is sitting along regions

R1A, R1B, and R2 are respectively noted as E_R₁_A, E_R₁_Band E_R₂.

The relative stability of the complexes are discussed here by

(Figure 9 )

evaluating the energy diﬀerences ΔE

= E_R₂− E_R₁_Aand

R2−R1A

ΔE

= E − E gathered in Table 10.

R2−R1B

R2

R1B

Comparing adduct formation along regions R1B and R1A, it

is found most favorable when involving the former R1B region

in six out of eight molecules (ΔE

> ΔE_R₂₋_R₁_A), while it is

R2−R1B

more stable along the latter region for only two remaining ones

> 0,

(

ΔE

< ΔE

). For all molecules ΔE

R2−R1B

R2−R1A R2−R1B

establishing that adduct formation along region R1B is always

more stable than along region R2. On the other hand, adduct

formation along region R1A is more stable than along R2

(

ΔE

> 0) with ﬁve molecules. For two of the three

R2−R1A

Figure 9. Optimized structure of ﬂuoride adducts with COSS and

COSeSe. The structures of other ﬂuorine adducts were similar to that

observed for COSS and COSeSe. The absence of covalent bonds

between atoms should not be confused with the absence of a bonding

interaction (see text). Ch···F and Ch···Ch bonding interactions

showing 1< |V|/G < 2 are represented with dashed lines, whereas the

rest of bonds are covalent and exhibit |V|/G > 2.

< 0), namely [COSSe···F]⁻and

1

remaining cases (ΔE

R2−R1A

−

1

[

CSSSe···F] adducts, the interaction Se···F along region R2

leads to a relatively higher stability than that of S···F along

region R1A (negative ΔE_R₂₋_R₁_A). Besides, in the third case,

−

1

[

CSSS···F] , the slightly negative ΔE

value can be due

R2−R1A

−

to a slight repulsion between Ch1 and F atoms along region

R1A. Altogether, among the eight most stable conﬁgurations

six of them correspond to adducts formed along region R1B

and two along region R1A. The two latter correspond to

−

The optimization with F in the R1A region resulted in the

presence of a short and almost linear Ch3−Ch2···F interaction

in all eight adducts. The formation of the Ch2···F bonding

interaction results in the concomitant weakening of the Ch2−

Ch3 bond, as evidenced from the increase in the Ch2−Ch3

bonds lengths (Table 7; Table S16 ). The largest increase in

distance is observed for the S−S bond, while the smallest

increase is observed for the Se−Se bond. In comparison, the

changes in the C1−Ch2 and C7−Ch3 bond lengths were

relatively small.

−

1

−1

[

COSeS···F] and [CSSeS···F] , where the interaction Se···F

takes place with Se at Ch2 position. Hence, in all cases where

adduct forms via the Se···F interaction instead of the S···F at

the same position, the adduct is more stable, indicating that the

former interaction is energetically more stabilizing than the

latter.

2

.7.3. Topology of ρ(r) in Fluoride Adducts. The

topological parameters obtained at BCPs conﬁrm a signiﬁcant

weakening of the Ch2−Ch3 bond when the Ch2···F or Ch3···F

bonding formation is taking place along regions R1A or R1B,

respectively (Figures S24 and S25). Indeed, the magnitudes of

ρ, ∇ ρ, and |V|/G for the Ch2−Ch3 bond in the adducts are

signi ﬁ cantly lower than those obtained for the monomers

The results corresponding to the optimization in the R1B

region are largely similar to those observed in region R1A

(Tables 8 and S17 ). Thus, the formation of the Ch3···F

2

bonding interaction results in the concomitant weakening of

the Ch3−Ch2 bond, as evidenced from the increase in Ch3−

Ch2 bond length (Table S17 ). However, the stretching of the

Ch2−Ch3 bond upon adduct formation is less important as

compared to that observed in region R1A.

(

Tables S19 and S20 ). In many cases, the magnitude of ρ at

the Ch2···F (or Ch3···F) BCP is larger than at the Ch2−Ch3

BCP within the same adduct. The |V|/G descriptor for both

Ch2···F (or Ch3···F) and Ch2−Ch3 ranges between 1 and 2 in

all the complexes, demonstrating the partial covalent character

of both bonding interactions after adduct formation.

Comparing the results obtained for adducts formed along

regions R1A and R1B, the change in the topological

parameters at the Ch2−Ch3 BCP is more signiﬁcant when

the adduct forms via the region R1A, paralleling the trend

previously observed with the geometrical parameters (Tables 7

and 8). One contributing factor to this feature is the additional

formation of a C−H···F hydrogen bonding interaction when

the adduct formation takes place via the R1B region (Figure

Strikingly, the optimization of the ﬂuoride adducts within

the R2 region does not signiﬁcantly alter the molecular Ch2−

Ch3, C1 −Ch2, and C7−Ch3 covalent bond lengths (Table 9,

Table S18 ). In terms of the geometrical parameters associated

with the formation of either Ch2···F or Ch3···F bonding

interaction, a clear pattern is observed. Accordingly, if Ch2 =

Ch3 (i.e., in COSS, COSeSe, CSSS, and CSSeSe), then Ch3···

F is systematically shorter than Ch2···F, and C7−Ch3···F is

closer to linearity than C1−Ch2···F. For the other four adducts

where Ch2 ≠ Ch3, the Ch···F interaction is shorter and the

C−Ch···F moiety more linear with Ch = Se.

a

Table 7. Geometrical Parameters of Selected Fluoride Adducts via Region R1A (See Table S16 for Other Adducts)

d (Ch2···F) ∠ Ch3−Ch2···F d (Ch2−Ch3) Δd (Ch2−Ch3) d (C1−Ch2) Δd (C1−Ch2) d (C7−Ch3) Δd (C7−Ch3)

COSS···F]⁻

COSeSe···F]

CSSS···F]⁻

1

1.82

1.94

1.81

1.94

179.0

177.3

173.8

177.0

2.44

2.64

2.41

2.61

+0.35

+0.28

+0.30

+0.24

1.83

1.98

1.78

1.93

+0.00

0.00

+0.03

1.73

1.89

1.72

1.88

−0.03

−0.02

−0.04

−0.03

[

−

1

CSSeSe···F]⁻

1

a

Δd corresponds to the diﬀerence in the bond length observed between adduct and monomer, i.e. Δd = d(adduct) − d(molecule). Units: d (Å), Δd

Å), and ∠ (deg).

(

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a

Table 8. Geometrical Parameters of Selected Fluoride Adducts via Region R1B (See Table S18 for Other Adducts)

d Ch3···F

∠ Ch2−Ch3···F

d Ch2−Ch3

Δd Ch2−Ch3

d C1−Ch2

Δd C1−Ch2

d C7−Ch3

Δd C7−Ch3

COSS···F]⁻

1

1.98

2.05

1.98

2.05

178.4

177.6

178.7

177.2

2.30

2.55

2.26

2.52

+0.21

+0.19

+0.15

1.76

1.92

1.72

1.87

−0.07

−0.06

−0.03

1.77

1.93

1.77

1.92

+0.01

+0.02

+0.01

+0.03

[

−

1

COSeSe···F]

−

1

CSSS···F]

CSSeSe···F]⁻

1

a

Δd corresponds to diﬀerence in the bond length observed between adduct and monomer; i.e., Δd = d(adduct) − d(molecule). Units: d (Å), Δd

Å), and ∠ (deg)

(

a

Table 9. Geometrical Parameters for Selected Fluoride Adducts via Region R2 (See Table S18 for Other Adducts)

d Ch2···F ∠ Ch1−Ch2···F d Ch3···F ∠ Ch7−Ch3···F d Ch2−Ch3 Δd Ch2−Ch3 d C1−Ch2 Δd C1−Ch2 d C7−Ch3 Δd C7−Ch3

[

COSS···F]⁻

1

2.57

2.83

2.51

2.75

155.6

145.6

157.4

147.9

2.25

2.20

2.25

2.21

165.2

164.4

162.6

161.5

2.09

2.36

2.08

2.34

0.00

+0.00

−0.03

1.79

1.94

1.73

1.88

−0.04

−0.02

1.78

1.96

1.77

1.95

+0.02

+0.05

+0.01

+0.04

−

1

COSeSe···F]

−

1

CSSS···F]

CSSeSe···F]

−

1

a

Δd corresponds to diﬀerence in the bond length observed between adduct and monomer, i.e., Δd = d(adduct) − d(molecule). Units: d (Å), Δd

Å), and ∠ (deg)

(

−

1

Table 10. Stability of Fluoride Adducts ΔE (kcal mol )

three regions (R1A, R1B, and R2) possibly alter the

hybridization of the chalcogen atom after adduct formation,

as Ch2 (or Ch3) is bonded to three atoms with either partial

Relative to Those Involving the R2 Region

complex

COSS···F]⁻

COSSe···F]⁻

COSeS···F]⁻

COSeSe···F]

ΔE_R₂_‑_R₁_A

ΔE_R₂_‑_R₁_B

(

1 < |V|/G < 2) or fully covalent characteristics (|V|/G > 2).

1

[

6.27

−2.26

12.37

7.34

−0.14

−8.42

5.47

12.35

15.42

6.21

12.85

10.16

13.53

2.20

This would lead to a change in the hybridization of Ch2 (or

Ch3) from sp in monomers to partial sp d in adducts.

1

3

2

.7.4. Topology of L(r) = −∇ ρ(r). The topology of L(r)

−

1

with ﬂuoride adducts evolves not only with respect to that of

monomers at optimized geometries, but also with respect to

dimers extracted from the crystal structures, as a consequence

of the Ch···F bonding formation (Figure 10; Figures S27 −

S29 ). Indeed, in adducts, the interaction between the

chalcogen atom and the ﬂuoride anion is not purely closed-

shell in nature, since Ch···F bears a partial covalent character as

pointed from the topological analysis of ρ(r). In spite of this

partial shared-shell character, the L(r) map reveals a mostly

spherical VSCC region around the F atom. The reason is 2-

fold, (i) in the absence of a signiﬁcant polarization of ρ(r) in

the bonding region, the deformation of ρ(r) is hardly observed

for chemical bonds involving ﬂuorine atoms because of their

signiﬁcant electronegativity, and (ii) the large net charge of F

−

1

CSSS···F]

CSSSe···F]⁻

1

−

1

CSSeS···F]

CSSeSe···F]⁻

1

1.90

10.53

S25; Table S20), indirectly decreasing the strength of the

Ch3···F interaction that occurs simultaneously. The topo-

logical parameters clearly suggest that C−H···F is a secondary

2

interaction in the adduct with magnitudes ρ, ∇ ρ, and |V|/G

signiﬁcantly lower than those observed for the stronger Ch3···F

interaction (Table S22 ).

On the other hand, only one Ch···F (Ch2···F or Ch3···F)

BCP is observed when the interaction takes place through

region R2 (Figure S26 ). The particular occurrence of BCP is

observed depending on whether the Ch2···F or Ch3···F

interaction is shorter and more linear within a given adduct,

following the geometrical trend observed after optimization.

Interestingly, the formation of either a Ch2···F or a Ch3···F

bonding interaction does not lead to a weakening of the Ch2−

Ch3 bond (in fact, even a slight increase in the magnitude of

the topological parameters at the Ch2−Ch3 BCP is observed,

Table S21 ). The changes in the magnitude of the diﬀerent

topological parameters at either the C1−Ch2 or the C7−Ch3

bond after adduct formation is small as compared to the

changes we observed for the Ch2−Ch3 bond during the

adduct formation via the R1A and R1B regions. In addition,

(

q ∼ − 0.6 e) makes ρ(r) around ﬂuorine similar to that of an₋

halide with partial charge. Indeed, as previously observed for I

(

q ∼ −0.5 e) participating in the formation of polyiodide

49

chains, here no (3,−3) CP arises that could act as a

nucleophilic CC site in the F-basin. Instead, this atom should

be rather considered as a spherical nucleophile with net

−

negative charge q, like I in polyiodide chains. Given that both

selenium and iodine atoms exhibit a fully depleted valence-

shell region, the L(r) distribution, as well as the types and

disposition of CPs along the Se···F bond path, are very similar

−

to those observed along I···I bond paths in polyiodide chains,

where these bonding interactions also exhibit a partial covalent

character from the topology of ρ(r).

2

the magnitudes of ρ, ∇ ρ, and |V|/G at either Ch2···F or Ch3···

Once the S···F bonding interaction is established in adducts

F BCP are signiﬁcantly lower than those observed for the same

bonding interaction when involving the R1A and R1B regions.

Overall, this suggests that the Ch···F electrophilic−nucleo-

philic interaction is systematically more favorable along the

Ch2−Ch3 bond (R1A and R1B regions) than perpendicular to

it (R2 region). This is consistent with the energy of the

optimized ﬂuoride adducts and their relative stability along

regions R1A, R1B, and R2. It is also important to note that the

formation of Ch2···F or Ch3···F bonding interaction across all

with sulfur at Ch2 (F sitting in region R1A) or at Ch3 (F

2

sitting in region R1B) position, the reactivity surface ∇ ρ(r) =

0 of sulfur shrinks (Figures 10 and S27−S29), showing more

openness than in the corresponding optimized monomers and

in dimers at crystalline geometries. Concomitantly, whereas the

associated electrophilic site (CP1a or CP1b) in the open

reactivity surface remains very close to the position found in

monomers and dimers, the plane of charge concentration

P

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Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 10. L(r) maps in ﬂuoride adducts of COSS (top) and COSeSe (bottom). Bond critical points (small light green spheres), (3,+1) CPs (pink

spheres) and (3,−1) CPs (dark green spheres) are depicted around Ch2, Ch3, and F atoms. A (3,+3) CP (violet sphere) is found for a H atom that

makes a hydrogen bonding interaction with F in region R1B. See Figure S22 for other adducts.

where the lone-pairs stand reorients around the S atom. This

signiﬁcantly less that when the attack is along region R1A or

R1B. At the optimized geometry, F stands closer to Ch3 (= S)

and closely aligned to the C−Ch3 direction (i.e., in [COSS···

reorientation can be also attributed in part to the change in the

3

hybridization of Ch2 (or Ch3) from sp (in monomers) to a

3

−

−1

partial sp d after adduct forms with F , accommodating the

three Ch−F, C−Ch and Ch−Ch bonding interactions and the

lone-pairs plane around the central Ch-atom. Hence, it shifts

from the direction bisecting the angle ∠C−Ch2−Ch3 (or

F] or [CSSS···F] ), as the reactivity surface for Ch3

encloses a thin charge concentration region where CP2b

stands, while for Ch2 the region is thick around CP2a. On the

other hand, the S···F interaction does not aﬀect the Ch2−S

bond, which conserves its covalent character, while the charge

concentration region where CP3b and lone-pairs stand

reorients from the direction bisecting the angle ∠C−Ch3−

Ch2 toward the Ch2−Ch3 bond, approaching the direction

with an angle of 31.9° (see Figure S30). Whatever the region

R1A, R1B, or R2 along the adduct forms, the nucleophilic

power of the CC sites increases from monomers to adducts

∠

C−Ch3−Ch2) in the monomers toward the C−S bonding

direction in adducts, exceeding/approaching the C−Ch2/C−

Ch3 direction (Ch2, Ch3 = S) with an angle of 14.3°/8.3° (see

Figure S30 ). As a consequence, the CP3c-f sites that are in the

close vicinity of the lone-pairs plane shift in a similar way in

comparison to monomers (see Figures 10 and S27 −S29 ),

indicating that all the electron distribution around the plane is

concerned by this eﬀect. The reorientation of the lone-pairs

plane permits a favorable nucleophilic attack straightforwardly

directed along the Ch2−Ch3 bonding direction, letting an

open region that avoids the steric hindrance with lone pairs

and adjacent groups, as carbonyl or thiocarbonyl in region R1A

or the C−C(H) moiety in region R1B. Altogether, the actual

L(r) distribution in adducts clearly shows the charge

redistribution that has permitted the formation of the partial

covalent bond S···F after nucleophilic attack. At the opposite

side, the Ch2−Ch3 bond is weakened because its bonding

region of charge concentration shrinks, splitting in two regions,

each belonging to one chalcogen atom. In addition, if the

chalcogen atom that is not involved in the S···F bond is a sulfur

−

2

(for example, in COSS, L/ρ = 9.24 and 9.74 Å for Ch2 and

−

1

−2

Ch3, and in [COSS···F] , L/ρ = 9.97 Å for Ch2 along

−

2

region R1A, and 10.23 and 9.89 Å for Ch3 along regions

R1B and R2).

In the case of adducts showing the Se···F bonding

interaction along region R1A or R1B, the reactivity surface

remains largely open around selenium, showing a valence-shell

completely depleted and almost unchanged with respect to this

in the corresponding monomers. As previously observed for

the sulfur atom, the electrophilic site CP1a (or CP1b) in

selenium remains very close to the position found in the

monomers, while the charge concentration plane where lone-

pairs stand reorients toward the C−Se bonding direction in

adducts (exceeding/approaching the C−Se direction with an

angle of 12.3°/2.5° at Ch2/Ch3 position; see Figure S31).

Close to the lone-pairs plane, CP3a/CP3c sites at Ch2 and

CP3b/CP3d sites at Ch3 also follow the same eﬀect (Figure

atom (i.e., in [COSS···F]⁻or [CSSS···F] ), its reactivity

surface appears more closed. On the other hand, when the

nucleophilic attack takes place along region R2, the S···F

bonding interaction also shrinks the reactivity surface but

1

−1

Q

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Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

0). As for S···F, this reorientation permits the formation of

pubs.acs.org/crystal

Article

1

geometry of Ch···F within the adduct (aligned along the Ch2···

Ch3 direction in regions R1A and R1B, and deviated from

linearity with respect to the C···Ch direction in region R2),

which seems to be the result of a minimized repulsion

geometry of localized electrons (as in the VSEPR model) when

considering the disposition of the partial covalent Ch···F and

Ch···Ch bonding interactions, the covalent bond C···Ch, and

the Se···F bond straightforwardly along the Ch2−Ch3

direction after nucleophilic attack, avoiding steric hindrance

with lone pairs and adjacent molecular moieties. A further

signiﬁcant electronic eﬀect concerns the charge concentration

2

distribution (∇ ρ(r) < 0) in the bonding region of Ch2−Ch3,

which shrinks and shifts toward the chalcogen atom that is not

involved in the Se···F bonding interaction, as a consequence of

the weakening of the bond. On the other hand, when the

adduct forms along region R2, similar features to those

observed for S···F are also shown here. Hence, F stands closer

to Ch3 rather than to Ch2, while the Se···F bonding

interaction is weaker than that along regions R1A and R1B

and does not aﬀect the Ch2−Se bond. Besides, the lone-pairs

plane reorients, approaching the prolongation of the Ch2−Ch3

direction with an angle of 14.3° (see Figure S31) and letting

place for the Se···F bond. In addition, the nucleophilic power

of the CC sites also increases from monomers to adducts (for

3

the lone-pairs plane, with a partial sp d hybridization at the

central Ch-atom.

3. CONCLUSIONS

Diﬀerent 3H-1,2-benzodithiol-3-(thi)one derivatives and their

(

mixed) selenated analogs have been used here as a model

series to investigate the electrophilic character of disulﬁdes and

diselenides, which is believed to be involved both in their

chemical reactivity toward nucleophiles and in their role as

chalcogen bond donors in the solid state molecular assemblies.

The electrostatic potential (ESP) maps clearly establish the

presence of three σ-hole regions around the dichalcogenide

Ch2−Ch3 bond (R1A, R1B, and R2), exhibiting diﬀerent

amplitudes. The molecular packing of all the crystal structures

is mainly driven by π−π stacking interactions, forming columns

that are interlinked to each other via hydrogen and chalcogen

bonding. All three σ-hole regions participate in the formation

of chalcogen bonding interactions, with the shorter ones

involving region R2.

−

2

example, in COSeSe, L/ρ = 0.16 and 0.57 Å for Ch2 and

−

1

−2

Ch3, and in [COSeSe···F] , L/ρ = 0.70 Å for Ch2 along

region R1A, and 0.99 and 0.82 Å⁻for Ch3 along regions R1B

and R2). Compared to S···F, an increased degree of covalence

exhibits for the Se···F bonding interaction, which indeed shows

systematically larger ρ and |V|/G magnitudes at BCP when

2

[

CCh1Ch2Se···F]⁻¹is compared to the [CCh1Ch2S···F]⁻¹

series.

It is noteworthy that the characteristics of L(r) around S- or

2

The topologies of ρ(r) and L(r) = −∇ ρ(r) calculated at

Se-atoms bonded to F remain mainly unchanged along the

series of adducts. Thus, whatever the combination of the two

other Ch-atoms in the adduct, it does not bring any signiﬁcant

eﬀect on the L (r ) features around the chalcogen bonded to

ﬂuorine (Figures S27 −29 ). For all adducts, the CPs of L(r)

around the Ch2−Ch3 bond are very similar in type and

position than in monomers. Some exceptions are those close to

the Ch···F BCP or belonging to F (which are additional CPs),

and those standing close to the direction bisecting the angle <

C−Ch−Ch. Additional CPs can modify either the existence,

the type or the position of CPs that were formerly observed in

a close neighborhood in monomers, but they do not have any

signiﬁcant eﬀect on the others CPs of adducts. Along Ch···F,

CPs of (3,+1) and (3,−1) type in the valence-shell of the

atoms point in the bonding direction.

ﬁrst on isolated molecules give an accurate description of

electronic features associated with chalcogen atoms. The weak

nature of dichalcogenide Ch2−Ch3 bond is established from

the topological analysis of ρ(r), showing systematically lower

2

ρ, ∇ ρ and |V|/G values at BCP as compared to other covalent

bonds. For S- and Se-atoms, the topology of L(r) founds CC

sites at chalcogen lone-pairs positions, and CD sites at

electrophilic regions present around the Ch2−Ch3 bond. In

isolated molecules, the topological CD sites of most electro-

philic character are found in σ-hole regions identiﬁed by ESP

maps, supporting their electrophilic description.

In the crystal structures, CD and CC sites appear face-to-

face through intermolecular regions, involving σ-holes and lone

pairs. The directions of stronger CD···CC interactions show

mostly aligned to those of atoms bearing the CD and CC sites.

In all crystal structures, the angle between them is typically α <

∼15°, indicating that molecular orientation in the assembling is

driven by these local electrostatic electrophilic···nucleophilic

interactions between CD and CC sites. Most relevant

In summary, the reorientation of the plane containing the

lone pairs, along with the opening, shrinking, and splitting of

2

∇

ρ(r) = 0 surfaces, are the signature of the charge

redistribution that permits the nucleophilic attack to form

the partial covalent bonds S···F and Se···F. In contrast to the

observed interactions in crystalline structures, the interactions

of sulfur and selenium with ﬂuorine in adducts clearly show

their not negligible degree of covalence. Indeed, in addition to

the topological features of ρ(r) already raised, the electron

distribution around S- and Se-atoms signiﬁcantly reorganizes in

adducts, leading to a an important modiﬁcation of the

characteristic features of L(r) around the chalcogen atoms

involved in the bonding interaction with ﬂuorine, while in

intermolecular interactions their L(r) characteristics remain

similar to those found in monomers. Thus, the electronic

signature of the covalence degree of the Ch···F bonding

interaction, in not only observed from ρ and |V|/G magnitudes

at BCP (signiﬁcantly larger than in the molecular assembly of

crystalline structures) but also from the reorientation of the

plane containing the chalcogen lone pairs, which appears

necessary for reactivity. They are related to the anchoring

interactions involve performant CC and CD sites, which are

2

identiﬁed by large Δ(L/ρ)/d

values (Δ(L/ρ) = (L/

CC···CD

ρ) − (L/ρ) ) and correspond to small α-angles. It is

CC

CD

noteworthy that types and disposition of CPs observed for

either the S- or the Se-atom do not change upon diﬀerent

intramolecular environments along the series of monomers,

and only their positions are modiﬁed slightly in the dimers

extracted from the crystal structures. Accordingly, the

topological descriptors obtained for CC and CD sites in

monomers can be eﬃciently used for predicting molecular

assemblies.

The topological descriptors of ρ(r) conﬁrm that all three

possible σ-hole regions are involved in the assembling of

2

molecules, with larger ρ, ∇ ρ, and |V|/G magnitudes observed

at the intermolecular BCPs entailing region R2. The

electrophilic power of the CD site (L/ρ)_C_Din region R2 is

more important than most of those observed in regions R1A

R

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and R1B, resulting in intermolecular interactions of greater

4. EXPERIMENTAL SECTION

2

intensity. Δ(L/ρ)/d

magnitudes also demonstrate that

CC···CD

4,1. Syntheses. 4.1.1. 3H-1,2-Benzothiaselenol-3-one (COSeS).

2,2′-Dithiodibenzoic acid (1.5 g, 5 mmol, 1 equiv) and triphenyl-

phosphine selenide (5 g, 15 mmol, 3 equiv) were added to an oven-

dried 100 mL round-bottom ﬂask, and high vacuum was applied for

important electrophilic sites present along the Ch2−Ch3

bonding direction (regions R1A, R1B) are not involved in the

most intense electrophilic−nucleophilic interactions, which

rather concern the Ch2−Ch3 side-on interaction with a

nucleophile. In molecular assemblies involving S atoms, CD

sites are accessible along the Ch2−Ch3 bonding direction in

regions R1A and R1B, whereas their position in Se-atoms make

them less well placed due to their proximity to the basin of the

bonded carbon atom (which can lead to steric hindrance with

15−20 min. Then, freshly distilled 1,4-dioxane (50 mL) was added to

the round-bottom ﬂask under argon, and the reaction mixture was

then reﬂuxed for 3 days by monitoring the progress of reaction using

TLC. The reaction mixture was cooled to room temperature, and the

precipitated triphenylphosphine oxide was ﬁltered oﬀ as colorless

crystals. The solution was concentrated using rotary vapor under

reduced pressure, and the thus obtained crude was subjected to ﬂash

column chromatography for puriﬁcation to aﬀord COSeS (415 mg,

2

the C = Ch1_s_pgroup), in spite they present a signiﬁcantly

2

0%) as a yellow solid. R = 0.4 (EtOAc−petroleum ether, 1:9, v/v).

stronger electrophilic power than S atoms. The position of lone

pairs in the planes perpendicularly bisecting the ∠C−Ch−Ch

angles make the electrophilic sites close around these planes

less useful as anchoring sites for molecular assembling, because

eventual nucleophilic centers will feel the repulsion exerted by

the lone pairs that are in the vicinity.

For S- and Se-atoms, the reactivity surface analysis points

that nucleophilic attack is more favorable along the Ch2−Ch3

bond (regions R1A and R1B) than in perpendicular geometry

f

1

Mp: 80−81 °C. H NMR (300 MHz, CDCl ): δ 7.28−7.34 (m, 1H),

3

1

3

7

.57−7.64 (m, 2H), 7.90−7.92 (m, 1H). C NMR (300 MHz,

CDCl ): δ 125.3, 125.8, 127.6, 133.2, 133.3, 149.3, 197.3. Anal. Calcd

3

for C H OSSe: C, 39.08; H, 1.87; S, 14.90. Found: C, 40.88; H, 2.47;

7

4

S, 14.55.

4.1.2. 3H-1,2-Benzodiselenol-3-one (COSeSe). 2,2′-Diselenodi-

62

benzoic acid (1 g, 2.5 mmol, 1 equiv) and triphenylphosphine

selenide (2.55 g, 7.5 mmol, 3 equiv) were added to an oven-dried 100

mL round-bottom ﬂask, and high vacuum was applied for 15−20 min.

Then, freshly distilled 1,4-dioxane (50 mL) was added to the round-

bottom ﬂask under argon, and the reaction mixture was then reﬂuxed

for 3 days by monitoring the progress of reaction using TLC. The

reaction mixture was cooled to room temperature, and the

precipitated triphenylphosphine oxide was ﬁltered oﬀ as colorless

crystals. The solution was concentrated using rotary vapor under

reduced pressure, and the thus obtained crude was subjected to ﬂash

column chromatography for puriﬁcation to aﬀord COSeSe (130 mg,

(

region R2). Clearly, the involvement of CD sites in molecular

assembling should be distinguished from nucleophilic attack.

Indeed, while the former is mainly electrostatic with long

contact distances (closed-shell interaction), in the latter,

molecular electron clouds interpenetrate giving rise to a

reorganization of the electron distribution that permits to

generate new chemical bonds made by shared-shell inter-

actions. Hence, although the nucleophilic attack is more

diﬃcult along a side-on approach to Ch2−Ch3 (region R2) in

1

0%) as a brown solid. R = 0.4 (EtOAc−petroleum ether, 1:9, v/v).

f

1

Mp: 90−91 °C. H NMR (300 MHz, CDCl ): δ 7.37 (ddd, 1H, J =

8

1

3

.0, 6.0, 2.0 Hz), 7.59−7.67 (m, 1H), 7.68−7.81 (m, 1H), 7.93 (dd,

2

the absence of a hole in the reactivity surface ∇ ρ(r) = 0, a

13

H, J = 8.0, 1.0 Hz). C NMR (300 MHz, CDCl ): δ 125.8, 128.0,

3

signiﬁcant electrostatic interaction can take place with the

intermolecular environment involving this favorable electro-

philic region, where the CD site and the ESP maximum appear.

Formal interaction of the 1,2-benzodithiol-3-(thi)one and

their selenated analogs with the ﬂuoride anion was used to

explore the reactivity of such dichalcogenides around the

Ch2−Ch3 bond toward nucleophilic attack. For all 24

optimized adducts, the Ch···F interaction bears a partial

covalent character as shown by the topological analysis of ρ(r)

1

29.8, 133.5, 134.28, 144.3, 198.0. Anal. Calcd for C H OSe : C,

7

4

2

32.09; H, 1.54. Found: C, 34.87; H, 2.01.

4.1.3. 3H-1,2-Benzodithiol-3-thione (CSSS) and 3H-1,2-Benzodi-

thiol-3-one (COSS). 2,2′-Dithiodibenzoic acid (500 mg, 1.63 mmol, 1

equiv) and phosphorus pentasulﬁde (1.45 g, 3.26 mmol, 2 equiv)

were added to an oven-dried 100 mL round-bottom ﬂask, and high

vacuum was applied for 15−20 min. Then, freshly distilled 1,4-

dioxane (50 mL) was added to the round-bottom ﬂask under argon,

and the reaction mixture was then reﬂuxed for 2 days by monitoring

the progress of reaction using TLC. The reaction mixture was cooled

to room temperature, and the precipitate formed was ﬁltered oﬀ as a

white solid. The solution is concentrated using rotary vapor under

reduced pressure, and the thus obtained crude was subjected to ﬂash

(

1< |V|/G < 2). In spite of this partial shared-shell character,

L(r) maps reveal a mostly spherical VSCC region around the F

atom. Its signiﬁcant electronegativity and net charge (q ∼ −

F

column chromatography for puriﬁcation to aﬀord CSSS (510 mg,

0

.6 e) make ρ(r) around ﬂuorine similar to that of an halide

63

9

3%) as a red solid, R = 0.45 (EtOAc−petroleum ether, 1:9, v/v).

f

with partial charge. The characteristic topological features of

The NMR data obtained for AD39 are in good agreement with the

reported one. Then, to a solution containing CSSS (200 mg, 1.1

mmol, 1 equiv) in CHCl (15 mL) and CH COOH (10 mL) was

−

L(r) in Se···F show similar to those previously observed for

−

I···I interactions in polyiodide chains.

3

Finally, the topological analysis of L(r) in adducts points out

the reorientation of the plane containing the chalcogen lone

pairs, along with the opening, shrinking and splitting of

added Hg(OAc)₂(867 mg, 2.73 mmol, 2.5 equiv) at room

temperature. The reaction was then continued for 4 h. The insoluble

precipitate in the reaction mixture was ﬁltered over Celite and washed

2

with DCM. The ﬁltrate was washed with saturated NaHCO solution

3

reactivity surfaces ∇ ρ(r) = 0. They are the signature of the

×

2 and extracted with DCM. The organic layers were combined,

charge redistribution in the reactivity process that permits the

nucleophilic attack. If steric hindrance with lone pairs is

removed by reorienting the plane they stand, the bonding

interaction will take place preferably along the Ch2−Ch3

direction. Indeed, along regions R1A and R1B, all F···Ch

interactions are energetically more favorable and their bonding

interactions stronger than along region R2, where the lone-

pairs plane is only partially reoriented, in particular with S

atoms. In all cases, the adduct is more stable when it forms

through an Se···F instead of an S···F bonding interaction at the

same position.

dried over Na SO , ﬁltered, and concentrated under reduced pressure

2

4

to aﬀord COSS (150 mg, 82%) as a dark red solid in pure form. R =

f

1

0

.4 (EtOAc−petroleum ether, 1:9, v/v). Mp: 74−75 °C. H NMR

(300 MHz, CDCl ): δ 7.41 (ddd, 1H, J = 8.0, 6.0, 2.0 Hz), 7.48−7.76

(m, 2H), 7.95 (dt, 1H, J = 8.0, 1.0 Hz). C NMR (300 MHz,

3

1

3

CDCl ): δ 124.7, 125.6, 127.3, 129.1, 133.5, 148.3, 193.9. Anal. Calcd

3

for C H OS : C, 49.98; H, 2.40; S, 38.11. Found: C, 50.35; H, 2.71; S,

7

4

2

3

8.04.

4

.1.4. 3H-2,1-Benzothiaselenol-3-thione (CSSSe) and 3H-2,1-

Benzothiaselenol-3-one (COSSe). 2,2′-Diselenodibenzoic acid (500

mg, 1.25 mmol, 1 equiv) and phosphorus pentasulﬁde (1.1 g, 2.5

mmol, 2 equiv) were added to an oven-dried 100 mL round-bottom

S

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Table 11. Crystallographic Data

compound

formula

formula moiety

FW (g mol⁻¹)

system

space group

a (Å)

b (Å)

COSS

C H O S

COSeSe

COSeS

COSSe

CSSSe

C H O Se

C H O S Se

C H OSSe

C H S Se

1

4

8

2

4

14

8

2

4

14

8

2

7

4

7

4 2

2(C H OS )

2(C H OSe )

2(C H OSSe)

C H OSSe

C H S Se

7 4 2

7

4

2

7

4

2

7

4

7

4

336.44

monoclinic

524.04

monoclinic

430.27

monoclinic

215.12

monoclinic

C2/c

11.5460(9)

8.1932(6)

15.5611(12)

90.00

103.699(3)

90.00

1430.18(19)

296(2)

8

1.998

5.458

231.18

monoclinic

C2/c

13.0697(5)

7.9082(3)

15.3352(7)

90.00

104.060(2)

90.00

1537.53(11)

296(2)

8

1.997

5.337

P2 /c

P 2 /c

1

11.0152(13)

8.5169(9)

15.3506(18)

90.00

104.094(7)

90.00

1396.8(3)

296(2)

4

11.0799(9)

8.7669(6)

15.5042(10)

90.00

103.039(3)

90.00

1467.19(18)

296(2)

4

10.9280(7)

8.5589(5)

15.2459(9)

90.00

102.294(2)

90.00

1393.27(15)

100(2)

4

c (Å)

α (deg)

β (deg)

γ (deg)

V (Å³)

T (K)

Z

D_c_a_l_c(g·cm⁻¹)

1.60

0.676

2.372

9.998

2.051

5.603

μ (mm⁻

1

)

total reﬂs

θ_m_a_x(deg)

abs corr

T_m_i_n, T_m_a_x

uniq. reﬂs

R_i_n_t

9383

27.514

multiscan

0.952, 0.967

3184

11832

27.554

multiscan

0.142, 0.301

3303

216278

52.493

numerical

0.341, 0.539

16118

8587

27.476

multiscan

0.331, 0.721

1636

6594

27.572

multiscan

0.208, 0.808

1764

0.0202

0.0638

0.035

0.0375

0.0502

uniq. reﬂs (I > 2σ(I))

R₁

2413

0.0361

2011

0.0715

12518

0.0254

1260

0.0274

1412

0.0355

wR (all data)

2

0.0939

0.1303

0.0424

0.0642

0.101

GOF

res. dens. (e Å⁻³)

1.042

0.293, −0.262

1.144

1.195, −1.616

1.030

0.78, −0.66

1.044

0.458, −0.566

1.026

0.619, −0.422

ﬂask, and high vacuum was applied for 15−20 min. Then, freshly

distilled 1,4-dioxane (50 mL) was added to the round-bottom ﬂask

under argon, and the reaction mixture was then reﬂuxed for 2 days by

monitoring the progress of reaction using TLC. The reaction mixture

was cooled to room temperature, and the precipitate formed was

ﬁltered oﬀ as a white solid. The solution was concentrated using

rotary vapor under reduced pressure, and the thus obtained crude was

subjected to ﬂash column chromatography for puriﬁcation to aﬀord

(SHELXL-97) by full-matrix least-squares procedures on F².⁶⁴The 2-

fold rotational disorder in COSeS was modeled using the PART

command. All non-H atoms of the molecules were reﬁned

anisotropically, and hydrogen atoms were introduced at calculated

positions (riding model), included in the structure factor calculations

but not reﬁned.

ASSOCIATED CONTENT

■

CSSSe (450 mg, 84%) as dark red solid, R = 0.45 (EtOAc−petroleum

f

1

ether, 1:9, v/v)). Mp: 128−129 °C; H NMR (300 MHz, CDCl ): δ

*

sı Supporting Information

3

7

.49 (ddd, 1H, J = 8.0, 7.0, 1.0 Hz), 7.70 (ddd, 1H, J = 8.0, 7.0, 1.0

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.cgd.0c00961.

1

3

Hz), 7.82 (dt, 1H, J = 8.0, 1.0 Hz), 8.26−8.29 (m, 1H). C NMR

(

300 MHz, CDCl ): δ 126.1, 126.9, 131.4, 132.7, 141.6, 151.4, 219.3.

3

2

Anal. Calcd for C H S Se: C, 36.37; H, 1.74; S, 27.73. Found: C,

7

4

2

Topological analysis of L(r) = −∇ ρ(r) and supporting

3

0

6.40; H, 2.09; S, 27.63. To a solution containing CSSSe (200 mg,

ﬁgures and tables (PDF)

.86 mmol, 1 equiv) in CHCl (9 mL) and CH COOH (6 mL) was

3

added Hg(OAc)₂(688 mg, 2.16 mmol, 2.5 equiv) at room

temperature. The reaction was then continued for 4 h. The insoluble

precipitate in the reaction mixture was ﬁltered over Celite and washed

Accession Codes

CCDC 2008936 −2008939 and 2012940 contain the supple-

mentary crystallographic data for this paper. These data can be

obtained free of charge via www.ccdc.cam.ac.uk/data_request/

cif , or by emailing data_request@ccdc.cam.ac.uk , or by

contacting The Cambridge Crystallographic Data Centre, 12

Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

with DCM. The ﬁltrate was washed with saturated NaHCO solution

3

×

2 and extracted with DCM. The organic layers are combined, dried

over Na SO , ﬁltered, and concentrated under reduced pressure to

2

4

aﬀord COSSe (140 mg, 75%) as dark red solid in pure form. R = 0.4

f

1

(

EtOAc−petroleum ether, 1:9, v/v). Mp: 83−84 °C. H NMR (300

MHz, CDCl ): δ 7.45 (ddd, 1H, J = 8.0, 7.0, 1.0 Hz), 7.65 (ddd, 1H, J

3

=

8.0, 7.0, 1.0 Hz), 7.71−7.74 (m, 1H), 7.97 (dd, 1H, J = 8.0, 1.0 Hz).

13

AUTHOR INFORMATION

C NMR (300 MHz, CDCl ): δ 126.1, 127.1, 127.2, 129.5, 130.5,

■

3

1

33.7, 194.9. Anal. Calcd for C H OSSe: C, 39.08; H, 1.87; S, 14.90.

7 4

Corresponding Authors

Found: C, 39.12; H, 2.20; S, 15.30.

Marc Fourmigue

Chimiques de Rennes), UMR 6226, Université de Rennes, F-

5042 Rennes, France; orcid.org/0000-0002-3796-4802;

́

− CNRS, ISCR (Institut des Sciences

4

.2. X-ray Structure Determinations. Details about data

collection and solution reﬁnement are given in Table 11. X-ray

diﬀraction measurements were performed on a Bruker Kappa CCD

diﬀractometer operating with a Mo Kα (λ = 0.71073 Å) X-ray tube

with a graphite monochromator for all compounds except COSeS.

The latter was collected on a Bruker D8 Venture instrument. The

structures were solved (SHELXS-97) by direct methods and reﬁned

3

Email: marc.fourmigue@univ-rennes1.fr

Enrique Espinosa − CNRS, CRM2, Université de Lorraine, F-

54000 Nancy, France; orcid.org/0000-0002-8911-1887;

Email: enrique.espinosa@univ-lorraine.fr

T

https://dx.doi.org/10.1021/acs.cgd.0c00961

Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

pubs.acs.org/crystal

Article

Authors

(11) Garrett, G. E.; Carrera, E. I.; Seferos, D. S.; Taylor, M. S. Anion

recognition by a bidentate chalcogen bond donor. Chem. Commun.

Rahul Shukla − CNRS, CRM2, Université de Lorraine, F-

2

(

016, 52, 9881−9884.

5

4000 Nancy, France

12) Ho, P. C.; Szydlowski, P.; Sinclair, J.; Elder, P. J. W.; Kubel, J.;

̈

Arun Dhaka − CNRS, ISCR (Institut des Sciences Chimiques

de Rennes), UMR 6226, Université de Rennes, F-35042

Rennes, France

Emmanuel Aubert − CNRS, CRM2, Université de Lorraine,

F-54000 Nancy, France

Vishnu Vijayakumar-Syamala − CNRS, CRM2, Université de

Lorraine, F-54000 Nancy, France

Olivier Jeannin − CNRS, ISCR (Institut des Sciences

Chimiques de Rennes), UMR 6226, Université de Rennes, F-

Gendy, C.; Lee, L. M.; Jenkins, H.; Britten, J. F.; Morim, D. R.;

Vargas-Baca, I. Supramolecular macrocycles reversibly assembled by

Te ···O chalcogen bonding. Nat. Commun. 2016, 7, 11229.

(

13) Benz, S.; Lopez-Andarias, J.; Mareda, J.; Sakai, N.; Matile, S.

Catalysis with Chalcogen Bonds. Angew. Chem., Int. Ed. 2017, 56,

12−815.

14) Huynh, H.-T.; Jeannin, O.; Fourmigue, M. Organic

́

8

(

selenocyanates as strong and directional chalcogen bond donors for

crystal engineering. Chem. Commun. 2017, 53, 8467−8469.

3

5042 Rennes, France; orcid.org/0000-0002-1411-5656

(15) Jeannin, O.; Huynh, H.-T.; Riel, A. M. S.; Fourmigue, M.

́

Chalcogen bonding interactions in organic selenocyanates: from

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.cgd.0c00961

cooperativity to chelation. New J. Chem. 2018, 42, 10502−10509.

(16) Kang, J. M.; Ferrell, A. J.; Chen, W.; Wang, D. F.; Xian, M.

Cyclic Acyl Disulfides and Acyl Selenylsulfides as the Precursors for

Persulfides (RSSH), Selenylsulfides (RSeSH), and Hydrogen Sulfide

Notes

The authors declare no competing ﬁnancial interest.

(H S). Org. Lett. 2018, 20, 852−855.

2

(17) Salvetti, R.; Martinetti, G.; Ubiali, D.; Pregnolato, M.; Pagani,

ACKNOWLEDGMENTS

G. 1,2-Dithiolan-3-ones and derivatives structurally related to

leinamycin. Synthesis and biological evaluation. Farmaco 2003, 58,

■

This work has been supported by the French National Agency

for Research (ANR-17-CE07-0025-01 (Nancy) and ANR-17-

CE07-0025-02 (Rennes)). R.S. thanks the ANR for 1-year and

-months postdoctoral contracts. V.V.-S. thanks the ANR and

the region Grand-Est (France) for a 3-year Ph.D. contract

supported at 50/50). A.D. thanks the ANR for a 3-year Ph.D.

contract. The authors thank the EXPLOR mesocentre for

providing access to computing facilities (Project

019CPMXX0984/wbg13).

9

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95−998.

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https://dx.doi.org/10.1021/acs.cgd.0c00961

Cryst. Growth Des. XXXX, XXX, XXX−XXX

Article Doi

Understanding Reactivity and Assembly of Dichalcogenides: Structural, Electrostatic Potential, and Topological Analyses of 3 H-1,2-Benzodithiol-3-one and Selenium Analogs

DOI: 10.1021/acs.cgd.0c00961

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Full text of DOI:10.1021/acs.cgd.0c00961

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