An experimental and computational investigation of the site selective and lattice driven cycloaddition reactions of SNS+ salts with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and 1,1,2,2-tetracyanoethylene: Accounting for experimental findings for SNS+ cycloaddition reactions with other related multi cyano-containing compounds using DFT and VBT approaches

Available online at www.sciencedirect.com

Inorganica Chimica Acta 361 (2008) 521–539

www.elsevier.com/locate/ica

An experimental and computational investigation of the site

selective and lattice driven cycloaddition reactions of SNS⁺salts

with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and

1,1,2,2-tetracyanoethylene: Accounting for experimental ﬁndings

for SNS⁺cycloaddition reactions with other related multi

cyano-containing compounds using DFT and VBT approaches

a

b

a

a,

*

Andreas Decken , H. Donald B. Jenkins , Aaron Mailman , Jack Passmore

,

a

Konstantin V. Shuvaev

a

Department of Chemistry, University of New Brunswick, Fredericton, NB, Canada E3B 6E2

b

Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom

Received 19 April 2007; accepted 17 May 2007

Available online 2 June 2007

Dedicated to Professor Anthony J. Downs on the occasion of his 70th birthday

Abstract

Reaction of SNSSbF₆and DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone (1)) in SO₂solution in a 2:1 ratio aﬀorded the dicyclo-

addition product 1(SNS)₂(SbF₆)₂Æ SO₂in 85% isolated yield. The dicycloaddition product 1(SNS)₂(SbF₆)₂Æ SO₂was fully characterized

by IR, Raman, NMR, elemental analysis, and single crystal X-ray crystallography. The product of the site selective dicycloaddition of

SNS⁺at the nitrile functionalities of 1 represents the ﬁrst structurally characterized ortho-bis-1,3,2,4-dithiadiazolylium salt which adopts

a conformation that utilizes the intramolecular S^d+–O^dꢀelectrostatic interactions. The reaction of 1 and SNS[Al(OC(CF₃)₄] in a 1:1 ratio

yielded only the monocycloaddition product 1(SNS)[Al(OC(CF₃)₃)₄] indentiﬁed by multinuclear ¹³C, ¹⁴N, ¹⁹F, ²⁷Al NMR in SO₂solu-

tion. The assignment of the ¹³C NMR of 1(SNS)⁺in SO₂solution, were supported by comparison of the calculated (MPW1PW91/6-

31G^*) ¹³C NMR and experimental chemical shifts, and by comparison of the observed chemical shifts of the related 2(SNS)⁺produced

on reacting the mono-nitrile CDMQ (2-cyano-5,6-dichloro-3-methoxy-1,4-benzoquinone (2)) with SNS⁺(as the SbF₆salt). The reac-

ꢀ

tion of SNSSbF₆with TCNE (1,1,2,2-tetracyanoethylene (3)) gave the tri-cycloaddition product 3(SNS)₃(SbF₆)₃Æ SO₂(IR, Raman

microscopy and X-ray crystallography) in 40% yield.

The energetics of the cycloaddition reactions of SNS⁺with 1–3 and other multifunctional unsaturated centers (e.g. HC„C–CN, NC–

CN, CðCNÞ₃^ꢀ, o,m,p-(CN)₂C₆H₄, 1,3,5-(NC)₃C₆H₃, 4–10, previously reported, see Chart 1), were estimated in the gas phase

(MPW1PW91/6-31G^*), solution (PBE0/6-311G^*) and in the solid state by the ‘volume based thermodynamics’ (VBT) approach. The

general thermodynamic trends associated with the stepwise cycloaddition of SNS⁺with multifunctional nitriles were established. The

1:1 cycloaddition products were calculated to be stable in the gas phase and solution, while in the solid state the larger lattice enthalpy

of the 1:2 salt, relative to twice that of the 1:1 salt, favored the 1:2 cycloaddition product.

Keywords: 1,3,2,4-Dithiadiazolium; Symmetry allowed cycloaddition; Thermodynamics; DFT; VBT (volume-based thermodynamics); Calculated ener-

getics; SNS⁺; DDQ

*

Corresponding author. Tel.: +1 506 4534821; fax: +1 506 4534981.

E-mail address: passmore@unb.ca (J. Passmore).

doi:10.1016/j.ica.2007.05.033

522

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

1. Introduction

enthalpy contribution for both a 1:1 and 1:2 salt decreases

when the volume of the anion increases. Therefore, it has

been suggested that a strategy to obtain the monocycload-

dition product, as the predominate product, would be the

use of an SNS⁺salt of a very large anion (i.e.,

The general utility of SNS⁺as a synthon in sulfur–nitro-

gen chemistry [1] has been advanced by the convenient

large scale synthesis of SNSSbF₆[2a] and recent prepara-

tion of SNS[Al(OC(CF₃)₃)₄], which is soluble in CH₂Cl₂

[2b]. The quantitative, symmetry allowed cycloaddition

chemistry of SNS⁺with a variety of relatively simple deriv-

atives containing unsaturated centers (e.g., oleﬁns, acety-

lenes and nitriles) has been extensively investigated [3].

While other routes to both dithiadiazolylium isomers (R-

CNSNS⁺and R-CNSSN⁺) are known [4,6b], the reaction

of SNS⁺with a nitrile is essentially the only general, quan-

titative route to the 1,3,2,4-dithiadiazolylium isomer [3].

On reduction the R-CNSNS⁺gives the corresponding 7p

R-CNSNS^ꢀradical, which is isolable in some cases [5–9a],

but typically rearranges to the corresponding thermody-

namically more stable 1,2,3,5-dithiadiazolyl radical isomer

(R-CNSSN^ꢀ) [5]. This has provided access to a variety of

stable multiradicals, incorporating either one or both dithi-

adiazolyl isomers [6], from the corresponding multifunc-

tional nitriles and the readily available soluble SNSMF₆

(M = As, Sb). The physical and electronic properties of

these and related, stable sulfur–nitrogen radical heterocy-

cles are of current interest [7].

AlðOCðCF₃Þ₃Þ ^ꢀ), thereby reducing the lattice enthalpy

4

gain of the second cycloaddition (e.g., DH_s26 DH_s1) [10].

The isolation of the monocycloaddition products would

provide a free nitrile group, which is a potential reactive

site to introduce more diverse radical centers, (i.e.

ꢀCN þ ‘S₃^þꢀ’ ! ꢀCNS₃^þꢀ). In addition, the free nitrile

can act as a Lewis base in coordination to a transition

metal center (–CN ! M) [11d] and as an additional link

between neighboring molecules as a means of modifying

the bulk properties in the solid state (e.g., potentially giving

rise to ferromagnetism) [11a–c]. These possibilities have

motivated us to explore the stepwise cycloaddition of

SNS⁺with the strong electron acceptor 1 as a route to a

new class of hybrid quinoidal–thiazyl systems [12]. The

strong electron acceptors incorporating heavier main group

elements, especially fused heterocyclic rings containing the

quinoidal motif, are of central importance in the prepara-

tion of new conductive and magnetic materials, and have

been an active research area in materials chemistry [13].

In this paper, we report the reaction of the dinitrile 1

with both SNSSbF₆and SNS[Al(OC(CF₃)₃)₄]. Both the

1:1 and 1:2 cycloaddition products of 1 with SNSSbF₆,

1(SNS)⁺and 1ðSNSÞ₂^2þ, respectively, were identiﬁed in

SO₂solution by multinuclear NMR. However, only the

Typically, the reaction of SNS⁺with compounds con-

taining two or more nitriles results in the transformation

of every nitrile group to a 1,3,2,4-dithiadiazolylium moiety

[8], with the exception of K⁺[4] [9a] and 5(SNS)⁺[9b],

Chart 1.

ꢀ

1:2 cycloaddition product, 1ðSNSÞ₂^2þ, as the SbF₆salt,

In the case of K⁺[4] all three stepwise cycloaddition

products were isolated and characterized. More recently

the structure of the monocycloaddition product of

11(SNS)⁺has been determined by X-ray crystallography.

In addition, a thermodynamic explanation both in solution

and the solid state, for the preference of the dicycloaddition

was isolated in the solid state. Conversely, the reaction of

1 with SNS[Al(OC(CF₃)₃)₄] resulted only in the identiﬁca-

tion of the 1:1 cycloaddition product 1(SNS)⁺and unre-

acted starting materials in solution (multinuclear NMR)

and solid state (IR).

The reaction of 3 with an excess of SNSSbF₆in

SO₂solution yielded the 1:3 cycloaddition product,

3(SNS)₃(SbF₆)₃salt, in 40% isolated yield. We account

for the observations of these and related examples previ-

ously reported in the literature, based on our gas-phase

and solution DFT calculations and the ‘volume based ther-

modynamics’ (VBT) approach [14] in the solid state,

reported below.

2þ

products 11ðSNSÞ₂and 12ðSNSÞ₂from the reactions of

SNSMF₆(M = As, Sb) with 11 and 12, respectively [10],

has been presented. An example of the stepwise cycloaddi-

tion of SNSX (X = any anion) to any dinitrile dipolaro-

phile, (A), is given in the general Born–Fajan–Haber

enthalpy cycle in Fig. 1. The enthalpy of sublimation for

the dipolarophile (A) varies according to diﬀerences in

molecular weight (i.e., mp, T_fus) and van der Waal forces,

while the gas-phase terms (DH_g1, DH_g2) follow a general

trend. Typically, the magnitude and favorability of the

overall gas-phase reaction (DH_gas-phase) is determined by

DH_g1(e.g., A(SNS)⁺), which is always more favorable than

DH_g2, due to the Coulomb repulsions which result from the

addition of a second positive charge (e.g., AðSNSÞ₂^2þ). The

ionic strength term, I, for a 1:1 salt (I = 1) and a 1:2 salt

(I = 3), govern the relative magnitude of the lattice

enthalpy contribution in the solid state, according to Eq.

(D) (see below), while the sum of the individual ion vol-

umes is additive and variable,_ꢀonly depending on the size

2. Experimental

SNSSbF₆[2a] and SNS[Al(OC(CF₃)₃)₄] [2b] were pre-

pared and puriﬁed according to the literature procedures,

and the purity was conﬁrmed by IR. DDQ (2,3-dichloro-

5,6-dicyano-1,4-benzoquinone, 1, Aldrich, 98%) was used

as received. CDMQ (2-cyano-5,6-dichloro-3-methoxy-1,4-

benzoquinone, 2) was prepared and puriﬁed as described

in the literature [15] (contained traces of DDQ, ¹³C

NMR) and dried under dynamic vacuum prior to use.

TCNE (1,1,2,2-tetracyanoethylene, 3, TCI America, 98%)

was sublimed prior to use and the purity conﬁrmed by

IR. SO₂(Sulfur dioxide, Liquid Air, 99.999%) was stored

of the anion_ꢀ(e.g., AsF₆

AlðOCðCF₃Þ₃Þ

ðV ¼ 0:110nm³) versus

(V = 0.719 nm³)). Hence, the lattice

4

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

523

Chart 1. Multifunctional nitriles and their corresponding 1:1 and 1:2 cycloaddition products with SNS⁺.

over CaH₂for at least 24 h and freshly distilled prior to

use. CH₂Cl₂(spectroscopic grade) was reﬂuxed over

CaH₂and freshly distilled prior to use. Solids were manip-

ulated under a dry N₂atmosphere in an MBraun drybox

(O₂6 0.1 ppm and H₂O 6 0.1 ppm). Techniques and

apparatus for carrying out reactions in SO₂and CH₂Cl₂

in a closed greaseless Monel vacuum line, such that volatile

materials can be transferred quantitatively, have been

described elsewhere [16].

FT-IR spectra were recorded on a Thermo Nicolet

NEXUS 470 FT-IR (resolution 2 cm^ꢀ1) as Nujol mulls

between CsI and KBr plates. Raman spectroscopy samples

were sealed in dry melting point tubes and spectra were

recorded on a Bruker IFS66 FT-IR equipped with a Bruker

524

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

Fig. 1. A general Born–Fajan–Haber enthalpy cycle for the double cycloaddition of SNSX (X = any anion) and a dinitrile substrate (A).

FRA106 FT-Raman accessory using an Nd-YAG laser

(emission wavelength: 1064 nm; maximum laser power:

300 mW). Data were collected in the backscattering mode

(180ꢁ excitation, resolution 2 cm^ꢀ1). Raman microscopy

was performed on a Renishaw inVia RE 08 microscope

with enclosure using a HeNe laser (emission wavelength:

633 nm; maximum laser power: 17 mW) and a CCD detec-

tor. Data were collected using 20 scans from 3200–

100 cm^ꢀ1, resolution 4 cm^ꢀ1, and 10% laser power output.

NMR spectra were recorded on a Varian 400 NMR spec-

trometer in 10 mm NMR tubes that were ﬂame sealed

and were externally referenced to TMS (¹³C), neat nitro-

methane (¹⁴N), CFCl₃in SO₂(¹⁹F) and AlCl₃/D₂O

(²⁷Al). Elemental analyses were carried out by Galbraith

Laboratories, Inc., Knoxville, TN, USA.

Pyrex vessels of two types were employed throughout

unless otherwise stated. Type A, incorporating a water

cooled condenser with two 40 ml bulbs and closed by

two Rotoﬂo (6 HK) Teﬂon in glass valves. Type B, incor-

porating two limbs (50 ml) separated by a 10 mm medium

scintered frit and closed by two Rotoﬂo (6 HK) Teﬂon in

glass valves. One of the limbs contained a Teﬂon coated

magnetic stir bar. One piece 10 mm (o.d.) NMR tubes with

1/4 inch (6 mm, o.d.) Pyrex tube were connected to stain-

less steel Whitey^ꢂvalves (1KS4) by Swagelok^ꢂcompres-

sion ﬁttings, using Teﬂon back and front ferrules. The

Whitey^ꢂvalves were attached directly to the vacuum line

by 1/4 in. Monel tubing. The in situ NMR were obtained

in a one piece 10 mm (o.d.) NMR tube, directly attached

to the vessel by a 1/4 inch (6 mm) tube, and ﬂame sealed.

(See Figure S28 in supplemental material for diagrams of

the reaction vessels).

ꢁ10 ml by the removal of solvent under dynamic vacuum.

The yellow-orange solution, containing the more soluble

material was carefully decanted into bulb 2. The solvent

was recondensed back into bulb 1 and the more soluble

portion again decanted to bulb 2. This process was

repeated twice more. The volatiles were removed under

dynamic vacuum, leaving orange crystals in bulb 1 and a

yellow-orange powder in bulb 2. The water contained in

the condenser part of the vessel was rinsed with acetone

and dried with a stream of dry N₂before collecting the con-

tents of the vessel in the dry box. The orange crystalline

product (8.496 g, 10.0 mmol; 86% yield based on 1, Eq.

(1) was collected and sealed in Pyrex sample tubes under

N₂and stored at ꢀ20 ꢁC in order to avoid loss of any

SO₂of solvation. IR(CsI, nujol mull, cm^ꢀ1) with tentative

assignments [17]: 3344vw (m C@O overtone), 3314vw (m

C@O overtone), 1689 s (m_symC@O), 1667 s (m_asymC@O),

1574 s (m_symC@C), 1416 m (m C@N), 1321w (m_asymSO₂),

1262s (m_asymC–C), 1184s (m_symSO₂), 1086s (m_symC–C),

980w (m [S–N]), 948w, 919w, 897w, 876w, 756m (m [S–N]),

657vs ðm₃SbF₆^ꢀÞ, 588w, 574m, 539w (m_bendSO₂), 487w,

457m, 447m (–CNSNS, ring bend), 421w, 377m (C@O

bend), 287vs ðm₄SbF₆^ꢀÞ. FT-Raman (laser power, 68.8%,

500 scans): 1686(83) (m_symC@O), 1667(100) (m_asymC@O),

1638(75), 1574(50) (m_symC@C), 1437(52), 1416(54) (m

C@N), 1321(30) (m_asymSO₂), 1258(23) (m_asymC–C),

1107(25) (m_symSO₂or m_symC–C), 980(21), 897(26),

803(41), 720(20), 668(25), 648(67) ðm₁SbF₆^ꢀÞ , 576(46)

ðm₂SbF₆^ꢀÞ, 486(31), 378(16), 332(20), 286(26) ðm₅SbF₆^ꢀÞ,

261(23), 199(21). Anal. Calc. for C₈Cl₂F₁₂N₄O₂S₄Sb₂: C,

11.24; N, 6.56; S, 15.01. Found: C, 11.17; N, 6.63; S,

14.72%. Actual spectra are given in the supplemental mate-

rial (Figure S4, S7, S8). Assignments for the experimental

and calculated IR and Raman frequencies are given in

Table S5a in the supplemental material.

2.1. Synthesis of 1(SNS)₂(SbF₆)₂Æ SO₂

Caution! Precautions should be taken to avoid explosion

hazard when heating liquid SO₂in a closed vessel (well ven-

tilated fumehood, leather gloves, face shield, carefully built

glass vessel).

2.2. In situ multinuclear NMR study in SO₂solution of the

reaction of 1 and SNSSbF₆in a 1:2 ratio

A mixture of 1 (2.621 g, 11.55 mmol) and SNSSbF₆

(7.473 g, 23.81 mmol) were loaded to a vessel of Type A

and heated in 20 ml of SO₂at 50–60 ꢁC for 7 days. (The

liquid SO₂was prevented from condensing to the cooler

second bulb by closing the valve and isolating the con-

denser and reaction mixture, see Figure S28.) The resulting

yellow–orange solution over a large quantity of orange

crystals was concentrated by reducing solvent volume to

Similar to the reaction described in Section 2.1, a mixture

of

1

(1.164 g, 5.13 mmol) and SNSSbF₆(3.179,

10.13 mmol) was loaded to a vessel of Type A with a

10 mm (o.d.) NMR tube attached (See Figure S28). 20 ml

of SO₂was condensed, and the mixture heated at 50–

60 ꢁC for 4 days. A small portion (ꢁ4 ml) of the orange-

brown solution, over an orange crystalline solid, was

poured into the attached 10 mm NMR tube and ﬂame

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

525

sealed. The orange crystalline solid was washed and col-

lected in the drybox (1(SNS)₂(SbF₆)₂SO₂, IR) 3.516 g,

4.1 mmol, 81% yield; based on SNSSbF₆, Eq. (1). ¹³C

NMR (100.6 MHz, SO₂, r.t.); Obs. for 1ðSNSÞ₂^2þ: d

189.9, –CNSNS; 174.6, –C@O; 143.1, –C–Cl; 133.9,

–C(CNSNS); Obs. for 1(SNS)⁺: d 190.4, –CNSNS; 175.6,

–C@O; 170.5, –C@O; 144.3, C–Cl; 141.7, –C–Cl; 136.3,

C–CNSNS; 122.5, –C–CN; 111.4 –CN; Obs. for 1: d

170.7, –C@O; 142.5, C–Cl; 128.2, –C–CN; 110.4, –CN

and several weak unassigned resonances; ¹⁴N NMR

days in a Pyrex vessel of Type B (see Figure S28), giving

a brown solution over a small amount of very ﬁne white

solid. The brown solution was ﬁltered and the volatiles

removed under dynamic vacuum yielding an orange

brown solid, collected (2.586 g, 97% based on SNS[Al-

(OC(CF₃)₃)₄] and Eq. (2) in the drybox. IR (CsI, nujol,

cm^ꢀ1) with tentative assignments [17] for 1(SNS)⁺:

3345vw (C@O overtone), 3324vw (C@O overtone),

2235w (m CN), 1694 m,sh (m_symC@O),1675s (m_asym

C@O), 1556s (m_symC@C), 1095m (m C–C str), 1043w,

916w (m [S–N]), 897w (ring bend), 871w, 845m(m [S–N]),

727s, 696m,sh (ring bend), 669m (ring deformation),

561m (ring bend), 446s (-CNSNS ring bend), 377m

(C@O bend), 316w. The assignment of the frequencies

(28.9 MHz, SO₂, r.t.); Obs. for 1ðSNSÞ₂^2þ: d 20.0 (m_1/2

=

2876 Hz), –CNSNS; ꢀ23.9 (m_1/2= 2374 Hz), –CNSNS;

ꢀ95.5 (m_1/2= 7 Hz), SNS⁺; and NH ^þd ꢀ366. The ¹⁴N

4

NMR peaks were assigned based on Ref. [18a]. Actual spec-

tra are given in the supplemental material (Figure S19, S20

and Table S4). The calculated tentative assignments for

the NMR of 1(SNS)₂(SbF₆)₂are tabulated for comparison.

ꢀ

for the anion AlðOCðCF₃Þ₃Þ were identical with those

4

reported for H(OEt)₂[Al(OC(CF₃)₃)₄] [17]. For compari-

son, the IR of 1 was obtained (Nujol mull, KBr, cm^ꢀ1):

3340vw (C@O overtone), 3327vw (C@O overtone),

2247w (m CN), 2233w (m CN), 1695m,sh (m C@O),

1690m, sh, 1673s (m C@O), 1554s (m C@C), 1305w,

1269m, 1253m,sh, 1217w, 1174s, 1069w, 1009w, 958w,

932w, 897m, 802m, 653m,br, 457s, 376w. See supplemen-

tal material for actual spectra (Figure S1, S6) and IR fre-

quency assignments (Table S5).

2.3. Reaction of SNSSbF₆with an excess of 1

SNSSbF₆(0.425 g, 1.354 mmol) and

1

(0.611 g,

2.272 mmol) were placed in separate limbs of a Pyrex vessel

(Type B, see Figure S28). CH₂Cl₂(15 ml) and SO₂(5 ml)

was condensed on to 1 and SNSSbF₆, respectively. All

the solids dissolved on warming to room temperature giv-

ing a yellow solution in limb 1 (containing 1) and a yel-

low-brown solution in limb 2 (containing SNSSbF₆). The

two solutions were mixed in limb 1 giving a dark orange

solution and the mixture stirred for 12 h at room tempera-

ture. The resulting dark orange-brown solution over a

bright yellow-orange solid was ﬁltered to limb 2 and the

volatiles were removed under dynamic vacuum leaving an

orange-brown solid in limb 2. A small volume of fresh

SO₂(2 ml) was condensed on to the yellow-orange solid

in limb 1. The mixture was warmed to room temperature

and the yellow solution ﬁltered to limb 2. This process

was repeated twice more until the ﬁltrate was orange.

The volatiles were removed under dynamic vacuum. The

orange solid (0.476 g, 0.6 mmol, 82% yield based on

SNSSbF₆, Eq. (1) in limb 1 was identiﬁed as the 1:2 cyclo-

addition product, 1(SNS)₂(SbF₆)₂[IR]. The orange brown

solid in limb 2 (0.609 g) was mainly starting materials (1

and SNSSbF₆), with a small amount of cycloaddition prod-

uct. IR(CsI, nujol mull, cm^ꢀ1) with tentative assignments

[17]: 2227w (m CN, 1), 2193w (m CN), 1690 m,sh (m_sym

2.5. Multinuclear NMR study of the reaction of 1 and

SNS[Al(OC(CF₃)₃)₄] in a 1:1 ratio in SO₂solution

In a sealed 10 mm o.d. Pyrex NMR tube, 0.584 g of the

orange-brown solid was redissolved (Section 2.2) in SO₂

(5 ml). The NMR tube was inserted into a water cooled

metal reﬂux condenser and gently heated at 40–50 ꢁC.

¹⁴N NMR spectrum indicated that the reaction was incom-

plete (d ꢀ95 ppm, m_1/2= 7 Hz, SNS⁺[16a] after 4 days).

The multinuclear NMR {¹³C,¹⁴N,¹⁹F,²⁷Al} was periodi-

cally monitored at room temperature. After 16 days it

appeared that not all the SNS⁺had reacted (¹⁴N NMR).

¹³C NMR (100.6 MHz, SO₂, r.t.); Obs. for 1(SNS)⁺: d

191.1, –CNSNS; 176.3, –C@O; 171.1, –C@O; 171.0,

–C@O, 1; 145.3, C–Cl; 142.9, C–Cl, 1; 142.2, –C–Cl;

135.9, C–CNSNS; 128.4, –C–CN; 110.5, –CN, 1 and for

1

4

the anion AlðOCðCF₃Þ₃d122:2 (q, CF₃, J

¼ 292 Hz)

C–F

and d 79.9 (br, C(CF₃)₃); ¹⁴N NMR (28.9 MHz, SO₂,

r.t.): d 23.5 (m_1/2= 921 Hz), –CNSNS, ꢀ33.3 (m_1/2

=

691 Hz), –CNSNS, ꢀ95.3 (m_1/2= 626 Hz), –CN, plus a

superimposed peak for SNS⁺d ꢀ95); ¹⁹F NMR (376.3

MHz, SO₂, r.t.): d ꢀ73.9 [s, CF₃], ꢀ73.2 and ꢀ74.2 are

from small amount of decomposition of [Al^ꢀ]; ²⁷Al

NMR (104.2 MHz, SO₂, r.t.): d 36.8 [Al^ꢀ]. ð½ Al^ꢀꢂ ¼

AlðOCðCF₃Þ Þ^ꢀÞ[2b]. Actual spectra are given in the sup-

C@O,

1

or 1ðSNSÞ₂^2þ), 1675s (m_asymC@O,

1 or

1ðSNSÞ₂^2þ), 1498s,sh (SNS⁺) [2a], 1305m,br, 1262s (m_asym

C–C), 1183m (m_symSO₂), 1087s (m_symC–C), 975w, 919w,

897w, 876m, 846w, 800m, 761w (m [S–N]), 657vs

ðm₃SbF₆^ꢀÞ, 575m, 486w, 457m, 448m (-CNSNS, ring bend),

388s (C@O bend), 290vs ðm₄SbF₆^ꢀÞ.

3

4

plemental (Figure S23–S26) and observed (calculated) ¹³C

NMR chemical shifts are given in Table S4.

2.4. Reaction of 1 and SNS[Al(OC(CF₃)₃)₄] in a 1:1 ratio

in SO₂solution

2.5.1. Reaction of 3 and SNSSbF₆in 1:4 ratio in SO₂

solution

A mixture 1 (0.517 g, 2.28 mmol) and SNS[Al(OC(CF₃)₃)₄]

(2.195 g, 2.10 mmol) in 10 ml of SO₂was stirred for 7

10 ml of SO₂was condensed onto a mixture of 3

(0.322 g, 2.53 mmol) and SNSSbF₆(3.160 g, 10.06 mmol)

526

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

at ꢀ196 ꢁC in a Pyrex vessel of type A. A light yellow-

brown solution over a white solid at room temperature

was heated under reﬂux at 50–60 ꢁC for 12 days giving a

white-grey solid under a yellow-brown solution on cooling

to room temperature. The solubles were decanted into bulb

2 and the white-grey solid washed twice (ꢁ2 ml of SO₂)

until the ﬁltrate were colorless. The volatiles were removed

under dynamic vacuum giving a white-grey insoluble solid

(2.45 g) in bulb 1 and the more soluble yellow- brown

solid (0.936 g) in bulb 2. IR of the insoluble white-grey

solid (CsI, nujol, cm^ꢀ1): 2279 m (m CN), 2222w (m CN),

1305w, 1166s (m C@C), 1121w, 1099w, 966w, 948w, 919w,

889w, 851w, 812w, 773w, 650vs ðm₃SbF₆^ꢀÞ, 576m, 560m,

554m, 293s ðm₄SbF₆^ꢀÞ. The IR spectrum of the soluble frac-

tion indicated the presence of unreacted SNSSbF₆(Nujol

sealed Pyrex 10 mm o.d. NMR tube giving an orange solu-

tion over a bright yellow solid. Gentle agitation of the tube

for 5 min resulted in a dark orange solution with no undis-

solved solid. The NMR spectra were obtained after 12 h

¹³C NMR (100.6 MHz, SO₂, r.t.); Obs. (Calc. for

2(SNS)⁺): d 192.8 (190.8), –CNSNS; 177.3 (173.8) –C@O;

173.3 (168.6), –C@O; 162.5 (160.3), –COCH₃; 142.2

(155.6), –C–Cl; 141.7 (150.2);, –C–Cl; 113.7 (114.3),

–C(CNSNS); 67.6 (73.2), –OCH₃; Several weak resonances

observed for 2, Obs. (Calc. for 2): d 174.1 (176.7), –C@O;

172.5 (172.8), –C@O; 163.5 (160.1), –C–OCH₃; 140.8

(151.4), –C–Cl; 132.1 (146.1), –C–Cl; 114.1 (109.7),

–C–CN; not observed (104.4), –CN; 62.6 (67.2), –OCH₃;

1, impurity in 2; Obs. (Calc. for 1): d 171.0 (173.1),

–C@O; 142.9 (150.0), –C–Cl; 128.4 (129.4), –C–CN; 110.5

(109.8), –CN); ¹⁴N NMR for 2(SNS)⁺, (28,9 MHz, SO₂,

mull, KBr, cm^ꢀ1): 1498s, sh (SNS⁺) [2a], 657vs ðm₃SbF ^ꢀÞ

6

and an unidentiﬁed cycloaddition product: 2273w, 2187w,

1329s, 1291 m, 1152w, 1082w, 1036w, 1018w, 962w,

936w, 889w, 495w, 448w, 388m. For comparison the IR

spectrum of 3 (Figure S3) was obtained (Nujol mull, CsI,

cm^ꢀ1): 2261m (m CN), 2227w (m CN), 1328s, 1154s

(m C@C), 1115w, 1087w, 958m, 934w, 916w, 804w, 555m,

579m, 428w.

r.t.): d 16.5 (m_1/2= 4084 Hz), –CNSNS; ꢀ49.0 (m_1/2

=

1373 Hz), –CNSNS. Resonances for SNS⁺, d ꢀ95; NH₄^þ,

d ꢀ366; one unassigned resonance, d ꢀ218 ppm. See sup-

plemental materials for actual spectra (Figure S17–18, 1

and Figure S21–22 for 2(SNS)⁺) and Table S4 for compar-

ison of observed (calculated) ¹³C NMR tensors and full

assignments). IR spectrum of 2 (CsI, Nujol mull, cm^ꢀ1):

3387vw (C@O overtone), 3317vw (C@O overtone),

2227 m (m CN), 1704s (m_asymC@O), 1662s (m_symC@O),

1616s (m_symC@C), 1583s (m_asymC@C), 1524w, 1333m,

1285w, 1265w, 1239s, 1187w, 1174m, 1102m, 980m,

883m, 806m, 765w, 732m, 668vw, 608w, 557w, 503w,

464w, 444w, 415w, 385w. See supplemental material for

actual spectrum (Figure S2).

2.5.2. Preparation and isolation of crystalline

3(SNS)₃(SbF₆)₃Æ SO₂

3 (0.064 g, 0.5 mmol) and SNSSbF₆(0.634 g, 2.02 mmol)

were dissolved in 7 ml SO₂and allowed to stand for 12 days

at room temperature in one limb of Type B Pyrex vessel.

The pale yellow solution over a clear, colorless crystalline

solid was ﬁltered into the limb 2. The crystalline solid in

limb 1 was washed twice with two small portions of SO₂

and each time the more soluble portion ﬁltered into limb

2. The volatiles were removed under dynamic vacuum giv-

ing a colorless crystalline 3(SNS)₃(SbF₆)₃Æ SO₂, (0.235 g,

44% yield based on 3, Eq. (4). The IR spectrum of crystal-

line 3(SNS)₃(SbF₆)₃Æ SO₂(Nujol mull, CsI, cm^ꢀ1) and ten-

tative assignments [17]: 2230w (m CN), 1329s (m C@N or

m_asymSO₂), 1253w, 1181w, 1151m (m_symC–C or m_symSO₂),

1113w, 1081w, 1061vw, 1018vw, 976m (m [S–N]), 957m (m

[S–N]), 919vw, 892m, 811s, 659vs ðm₃SbF ^ꢀÞ, 572m (SNS

bend), 526m (m_bendSO₂), 478w, 438s (C„⁶N bend.), 389w,

287vs ðm₄SbF₆^ꢀÞ. Raman microscopy (laser power 10%,

20 scans): 2236(42) (m CN), 1578(100) (m C@C), 1444(41)

(m C@N, ring 2 and 3 (Fig. 4), 1396(43) (m C@N, ring 1

(Fig. 4)), 1328(20), 1261(19), 1252(20), 1151(48),

1030(16), 974(15), 955(17), 924(27), 879(14), 808(17),

788(21), 714(14), 644(31) ðm₁SbF₆^ꢀÞ, 582(24) (SNS bend

or m₂SbF₆^ꢀ), 563(15), 522(10), 277(11) ðm₅SbF₆^ꢀÞ. Actual

spectra are given in Figure S3 and S9 in the supplemental

material.

2.7. Crystal structure determinations

Suitable single crystals of 1(SNS)₂(SbF₆)₂Æ SO₂and

3(SNS)₃(SbF₆)₃Æ SO₂were obtained from SO₂solutions.

The SO₂was removed under dynamic vacuum (with lim-

ited exposure of crystals to prolonged dynamic vacuum

(5 min), since they are SO₂solvates), and the crystals col-

lected in the dry box. The suitable single crystals were

coated with Paratone-N oil in a sample vial and mounted

using a 20 lm cryoloop and frozen in the cold nitrogen

stream of the goniometer. Data were collected on a Bru-

ker AXS P4/Smart 1000 diﬀractometer using x and h

scans with a scan width of 0.3ꢁ and 30 s exposure times.

The detector distance was 5 cm for 1(SNS)₂(SbF₆)₂Æ SO₂

and 6 cm for 3(SNS)₃(SbF₆)₃Æ SO₂. In the case of

1(SNS)₂(SbF₆)₂Æ SO₂the crystal was a twin and the

orientation matrix for the major component determined

[19a]. The data were reduced [19b] and corrected for

absorption [19c]. The structures were solved by direct

methods and all atoms reﬁned anisotroically by full-

matrix least squares on F²[20]. All ﬁgures illustrating

crystal structures were prepared using the program DIA-

^MOND[21]. Crystal structure reﬁnement data for both

1(SNS)₂(SbF₆)₂Æ SO₂and 3(SNS)₃(SbF₆)₃Æ SO₂are given

in Table 1.

2.6. In situ multinuclear NMR study in SO₂solution of the

reaction of 2 and SNSSbF₆in a 1:2 ratio

A mixture of 2 (0.132 g, 0.569 mmol) and SNSSbF₆

(0.167 g, 0.532 mmol) in 7 ml of SO₂was prepared in a

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

527

refer to the reaction 1(S) + SNS⁺(S) ! 1 (SNS)⁺(S), where

(S) is solvent, taking place in (S) = SO₂and (S) = CH₂Cl₂

respectively. In Table 4 Entry 1 corresponds to the reac-

tion: K⁺[4](p) + SNSX(p) ! 4(SNS)(p) + KX(p), where

for column 3, X is absent and (p) = (g) representing the

gaseous phase, in column 4, X = SbF₆and (p) = (s); col-

umn 5, X = [Al] and in the ﬁnal column the results for

the reaction: K⁺[4](S)+ SNS⁺(S) ! 4(SNS)(S) + K⁺(S)

are given for (S) = SO₂as solvent.

The NMR tensors (at the MPW1PW91/6-31G^*level of

theory and 6-311G^*basis set used for Cl and S atoms) were

calculated by the GIAO method implemented in Gaussian

03W and referenced (¹³C, Benzene, D_6h) to obtain the cal-

culated chemical shift, according to Eq. (A)

Table 1

Crystal data and structure reﬁnement

1(SNS)₂(SbF₆)₂Æ SO₂

3(SNS)₃(SbF₆)₃Æ SO₂

Empirical formula C₈Cl₂F₁₂N₄O₆S₅Sb₂

Formula weight

CCDC deposit no. 635254

Temperature (K)

C₆F₁₈N₇O₂S₇Sb₃

1133.8

635255

173

0.71073

0.45 · 0.40 · 0.25

colorless, irregular

monoclinic

P2(1)/n

9.8155(8)

9.2621(7)

30.212(2)

90

96.742(1)

90

2727.64(5)

4

918.829

173

0.71073

0.60 · 0.20 · 0.15

yellow, irregular

triclinic

˚

Wavelength (A)

Crystal size (mm)

Color and habit

Crystal system

Space group

ꢀ

P1ð2Þ

˚

a (A)

8.0329(8)

8.4438(9)

18.514(2)

90.331(2)

97.467(2)

109.349(2)

1173.19(9)

2

˚

b (A)

˚

c (A)

a (ꢁ)

b (ꢁ)

c (ꢁ)

Volume (A )

Z

D_calc(Mg/m³)

Absorption

coeﬃcient

(mm^ꢀ1

Reﬂections

collected

13

dð CÞjCompoundj ꢀ dð CÞjBenzenej

¼ calculated chemical shift:

3

˚

ðAÞ

2.60087

3.098

2.76078

3.634

The referenced calculated chemical shifts were further cor-

related with the experimental chemical shift of benzene in

SO₂(¹³C NMR d 129.2) [18b] to obtain the correlated

chemical shift in SO₂solution according to Eq. (B)

)

7555

18235

13

Exp:dð CÞBenzene ꢀ calculated chemical shift

¼ Correlated chemical shift:

Independent

reﬂections

Index range

5012 [R_int= 0.0172]

6104 [R_int= 0.0221]

ðBÞ

ꢀ9 6 h 6 10,

ꢀ9 6 k 6 10,

ꢀ21 6 l 6 23

5012/334

ꢀ12 6 h 6 12,

ꢀ11 6 k 6 11,

ꢀ38 6 l 6 39

6104/388

Good agreement with the experimentally observed chemi-

cal shifts ( 5 ppm) was generally observed. The correlated

¹³C NMR chemical shifts for the C–Cl fragment were

always found to be larger than those observed experimen-

tally. This trend was relatively unchanged when using

larger basis sets at the MPW1PW91 level of theory. The

single point free energies in solution were calculated using

a polarization continuum model (PCM) with the integral

equation formalism (IEF) [24], employing the PBE0 DFT

hybrid functional [23b,23c] and using the gas-phase opti-

mized structures (conﬁrmed as minima by the absence of

imaginary frequencies) as inputs. The following parameters

were used to describe the solvent SO₂: dielectric constant

Data/parameter

Goodness-of-ﬁt on 1.163

F²

1.173

Final R indices

[I > 3r(I)]

R indices (all data) R₁= 0.0409,

wR₂= 0.0991

Largest diﬀerence

peak and hole

R₁= 0.0370,

wR₂= 0.0969

R₁= 0.0275,

wR₂= 0.0603

R₁= 0.0304,

wR₂= 0.0612

1.161 and ꢀ0.628

1.532 and ꢀ1.926

˚

(e/A)

2.8. Thermodynamic, electrostatic, and quantum chemical

calculations

˚

(Eps) = 14.0, solvent radius (R_solv) = 2.021 A, molar vol-

3

˚

ume (V(SO₂)) = 46.75 A = 0.0468 nm (use_ꢀd₃later in this

˚

paper), numeral density (q) = 0.01288 A

1.37027 g cm^ꢀ3

, density =

2.8.1. Quantum Chemical Calculations

.

All quantum-chemical calculations were carried out

using the DFT methods as implemented in ^GAUSSIAN03W

suite of programmes [22]. The gas-phase calculations were

carried out at the MPW1PW91 level [23a] with the 6-31G^*

basis set. Calculations are made for all the reactions listed

in the second column of Tables 2 and 4 in which all the spe-

cies listed are in the gas phase (e.g., Entry 1, Table 2, 1

(g) + SNS⁺(g) ! 1 (SNS)⁺(g)) and the numerical results

for the enthalpy change for these gas phase reactions are

displayed in column 3 of the tables. Entries in the fourth

and ﬁfth column refer to the corresponding reactions in

the solid state (e.g. Entry 1, Table 2: for reaction: 1

(s) + (SNS)SbF₆(s) ! 1 (SNS)(SbF₆) (s), DH is listed in

column 4 and for reaction: 1 (s) + (SNS)[Al] (s) ! 1

(SNS)[Al] (s), where [Al] = Al(OC(CF)₃)₄then DH is listed

in column 5). Columns 6 and 7 (which include a DG value)

Rough electrostatic estimates of internal electrostatic

potential energy were determined [25]¹, according to Eq.

(C),

E_pot¼ ½ð333^ꢃq^ꢃq₂Þ=rꢂ^ꢃ4:184 kJ mol^ꢀ1

ðCÞ

1

where the atoms were treated as point charges. The dis-

˚

tances (r, A) and Mulliken charges (Coulombs) were ob-

tained from the gas-phase calculations (MPW1PW91/

6-31G^*).

1

Only the major S^d+–N^dꢀinteractions and the most apparent N^dꢀ–N^dꢀ

interactions were determined as illustrated in Fig. 3. However, it was

found that the S^d+–N^dꢀinteractions are the most signiﬁcant and a number

of rotational isomers are envisioned.

528

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

Table 2

Calculated gas-phase and solution enthalpies (DH), solution Gibbs free energies (DG) and solid state estimates for 1, 2 and 3 (Chart 1)

Entry From Chart 1

Gas

phase^a

X^ꢀ¼ ½SbF₆^ꢀꢂ

X^ꢀ= [Al]^ꢀ

solid

SO₂solution CH₂Cl₂

solution

solid

DH

DH^b

DH

ꢀ103 ꢀ63

DG^c

DH

ꢀ104 ꢀ55

DG^c

1

2

3

4

5

6

7

8

1 (g) + SNS⁺(g) ! 1(SNS)⁺(g)

ꢀ159

1 (s) + SNSX (s) ! 1(SNS)X (s) (cycle A)

1ðSNSÞ^þðgÞ þ SNS^þð gÞ ! 1ðSNSÞ₂^2þðgÞ

+62

ꢀ21

+109

ꢀ50

ꢀ64 ꢀ19

ꢀ167 ꢀ97

ꢀ55 +1

ꢀ159 ꢀ70

+49 +50

1(SNS)X (s) + SNSX (s) ! 1(SNS)₂(X)₂(s) (cycle A)

ꢀ308

ꢀ246

ꢀ366

+248

+244

ꢀ218

ꢀ239

ꢀ193

+165

+161

1ðgÞ þ 2SNS^þðgÞ ! 1ðSNSÞ₂(g)

2þ

1 (s) + 2 SNSX (s) ! 1(SNS)²⁺(X)₂(s) (cycle A)

21ðSNSÞ^þðgÞ ! 1ðSNSÞ₂^2þðgÞ þ 1ðgÞ

+269

+27

+39

+74

+60

+88

+40

+15

+1

21(SNS)X (s) ! 1(SNS)₂X₂(s) + 1(s) (cycle B)

1 (g)+SNS⁺(g) ! 1ꢀA⁺(g) (Scheme 1)

1 (s) + SNSX (g) ! 1ꢀAX (s) (Scheme 1)

1 (g) + SNS⁺(g) ! 1ꢀB⁺(g) (Scheme 1)

1 (s) + SNSX (g) ! 1ꢀBX (s) (Scheme 1)

1 (g) + SNS⁺(g) ! 1ꢀC⁺(g) (Scheme 1)

1 (s) + SNSX (g) ! 1ꢀCX (s) (Scheme 1)

2 (g) + SNS⁺(g) ! 2(SNS)⁺(g)

+23

+41

+25

+262

Sublimation

enthalpy

+179

Sublimation

enthalpy

ꢀ185

ꢀ106 ꢀ61

of 2 unknown

3 (g) + SNS⁺(g) ! 3(SNS)⁺(g)

ꢀ100

+118

+412

+630

+218

ꢀ82

ꢀ71

ꢀ46

ꢀ30

3 (s) + SNSX (s) ! 3(SNS)X (s) (cycle C)

+44

ꢀ7

d

2þ

10

11

12

13

3ðSNSÞ^þðgÞ þ SNS^þðgÞ ! 3ðSNSÞ₂ðgÞ

3(SNS)X (s) + SNSX (s) ! 3(SNS)₂(X)₂(s) (cycle C)

ꢀ298

ꢀ216

2þ

3ðSNSÞ₂ðgÞ þ SNS^þðgÞ ! 3ðSNSÞ^3þðgÞ

Lattice energies not

available

Lattice energies not

available

ꢀ117 ꢀ100

3þ

3ðSNSÞ ðgÞ þ SNS^þðgÞ ! 3ðSNSÞ₄^4þðgÞ

Lattice energies not

available

Lattice energies not

available

+96

+11

+72

+8

23ðSNSÞ^þðgÞ ! 3ðSNSÞ₂^2þðgÞ þ 3ðgÞ

2 3(SNS)X (s) ! 3(SNS)₂(X)₂(s) + 3 (s) (cycle D)

ꢀ338

ꢀ206

.

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

529

Table 2 (continued)

.

a

Includes zero point energy (ZPE) correction.

Calculated from appropriate Born–Haber cycles illustrated below, using the calculated gas phase values, RT terms, and the volume based thermo-

b

dynamic (VBT) estimates of the lattice potential energies (see supplemental material for full details).

c

Including thermal correction to Gibbs free energy taken from the MPW1PW91/6-31G^*(gas-phase) frequency calculations.

Three isomers are possible for the second cycloaddition of SNS⁺with 3(SNS)⁺with respect to the –CNSNS ring (trans, cis or vicinal) of which, the

d

trans isomer (Chart 1) is the minimum in the gas-phase (MPW1PW/6-31G^*).

2.9. VBT and volume calculations

of 1(SNS)₂(SbF₆)₂Æ SO₂, as V_m= 1.17319/2 = 0.587 nm³

from the X-ray crystal structure (Table 1). As a result

of the work of Hofmann [14g], who has, on the basis of

analysis of the Cambridge Structural Database (CSD)

listed the average volumes assignable to various atoms

within crystal structures and thus provides a means of

estimating volumes of materials. Accordingly from sum-

mation of Hofmann’s atom volume data we can estimate

that V(1(SNS)₂(SbF₆)₂Æ SO₂) = V(C₈Cl₂F₁₂N₄O₆S₅Sb₂) =

0.634 nm³which is within 0.047 nm³of the volume as

determined by X-ray analysis of the actual compound.

The lattice potential energy (U_pot) of salts were esti-

mated using the volume based thermodynamic (VBT)

approach by Jenkins et al. [14a] according to Eq. (D),

U_pot¼ 2IðaV ^ꢀ_m¹⁼³þ bÞ

ðDÞ

For 1:1 salts (monocation and monoanion), a/kJ mol^ꢀ1

nm = 117.3, b/kJ mol^ꢀ1= 51.9, I = 1; For 1:2 salts (dica-

tion and two monoanions), a/kJ mol^ꢀ1nm = 133.5, b/

kJ mol^ꢀ1= 60.9, I = 3. Small errors in the volume are

mitigated by this method (i.e., U_pota V^ꢀ1/3), hence the

small contribution from the volume of the SO₂, V(SO₂)

of solvation to the total volume in both 1(SNS)₂(SbF₆)₂Æ

SO₂and 3(SNS)₃(SbF₆)₃Æ SO₂are minimal (although

using the volume above could be taken into account).

The lattice energy, on incorporation into the traditional

Born–Fajans–Haber enthalpy cycle requires correction to

an enthalpy term as described by Jenkins [14e,14f] by

the inclusion of the appropriate number of RT terms,

determined by the stoichiometry and the nature (geome-

try) of the complex ions which are involved in the lattice

energy stage(s).

ꢀ

The volume of the SbF₆anion is VSbF₆^ꢀÞ ¼ 0:121nm³

[14a], therefore since: V ð1ðSNSÞ₂^2þÞ ꢄ V ð1ðSNSÞ₂ðSbF₆Þ₂ꢅ

SO₂Þ ꢀ 2V ðSbF₆^ꢀÞ ꢀ VðSO₂Þ ¼ 0:587 ꢀ 2ð0:121Þ ꢀ 0:047 ¼

0:298 nm³. Alternatively using Hofmann’s data we can esti-

mate that: V ð1ðSNSÞ₂^2þÞ ꢄ V ðC₈O₂N₄S₄Cl₂Þ ¼ 0:332nm³.

The two values average to V ð1ðSNSÞ₂^2þÞ ꢄ 0:315 nm³.

Since V(SNS)⁺= 0.060 0.009 nm³and V ð1ðSNSÞ₂^2þÞ ¼

V ð1ðSNSÞ^þÞþ V ðSNSÞ^þ

we

can

now

estimate

V ð1ðSNSÞ₂^2þÞ ꢄ 0:315 þ 0:060 ¼ 0:375nm³.

Also from the crystallographic data presented in Table 1

it is determined that: V(3(SNS)₃(SbF₆)₃Æ SO₂) = 2.72764/

4 = 0.682 nm³(which matches the Hofmann data which

Based on X-ray structural determinations, an estimate

of a formula unit volume, V_m(i.e., V_m= V_cell/Z) can be

determined. Hence, for a given formula unit volume,

V_m, of a given salt, M_pX_q, the individual ion volume com-

ponents can be calculated (i.e., V_m(M_pX_q) ꢄ p(V(M^q+) +

q(V(X^pꢀ)) [14b]. Here we obtain the formula unit volume

gives

V(3(SNS)₃(SbF₆)₃Æ SO₂) ꢄ V(C₆F₁₈N₇O₂S₇Sb₃) =

0.710 nm³, only 0.028 nm³diﬀerent than our experimental

result). Since: V ð3ðSNSÞ₃^3þÞ ꢄ V ð3ðSNSÞ ðSbF₆Þ₃ꢅ SO₂Þꢀ

3V ðSbF₆^ꢀÞ ꢀ V ðSO₂Þ ¼ 0:682 ꢀ 3ð0:121Þ ³ꢀ 0:047 ¼ 0:272

nm³. Alternatively using Hofmann data we can estimate

that: V ð3ðSNSÞ₃^3þÞ ꢄ V ðC₆N₇S₆Þ ¼ 0:317nm³, which leads

530

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

to an average: V ð3ðSNSÞ₃^3þÞ ꢄ 0:295nm³. Also since:

V ð3ðSNSÞ₂^2þÞꢄV ð3ðSNSÞ₃^3þÞꢀV ðSNS^þÞ and V ð3ðSNSÞ^þÞ

ꢄ V ð3ðSNSÞ₂^2þÞ ꢀ V ðSNS^þÞ then the volumes of the ions

V ð3ðSNSÞ^x_x^þÞ can be estimated to be 0.235 ð3ðSNSÞ₂^2þÞ

and 0.175 nm³(3(SNS)⁺)) respectively. In general for any

N (Chart 1):

limation enthalpy is dependent upon the strength of elec-

trostatic interactions, dispersion forces, and dipole-dipole

interactions).

115 kJ mol^ꢀ1

Accordingly

we

take

DH_sub(1) ꢄ

.

3. Results and discussion

3.1. Cycloaddition chemistry of SNS⁺with 1

ðnþ1Þþ

nþ

V ðNðSNSÞ

Þ ꢀ VðNðSNSÞ_nÞ ꢄ V ðSNS^þÞ

nþ1

¼ 0:060 nm³:

ðEÞ

The cycloaddition reaction of SNS⁺, as the SbF₆salt,

with the nitrile functionalities of 1 (2:1 stiochiometry) in

reﬂuxing SO₂solution gave the corresponding dicycloaddi-

tion product, 1(SNS)₂(SbF₆)₂Æ SO₂in high yield (85%,

based on SNSSbF₆and Eq. (1). The dicycloaddition prod-

ucts are less soluble then the 1:1 salts and readily precipi-

tate or crystallize from SO₂solution. The preparation of

the mono-cycloaddition product, 1(SNS)(SbF₆), in a mix-

ture of SO₂and CH₂Cl₂was attempted, expecting the 1:1

product to be less soluble (CH₂Cl₂has a lower dielectric

constant than SO₂), but the dicycloaddition product

1(SNS)₂(SbF₆)₂Æ SO₂was obtained instead (IR, 82% yield)

[27]. The mono-cycloaddition product, 1(SNS)(SbF₆) was

not identiﬁed in the solid state by IR. However, an in situ

reaction (Eq. (1)) of two equivalents of SNSSbF₆and 1

in SO₂solution (¹³C, ¹⁴N NMR spectra are given in Figure

S19 and S20, respectively) gave a mixture of both 1:1 and

1:2 cycloaddition products after 4 days (ca. 2:1 ratio of

ꢀ

In this pap_ꢀer we also consider salts containing the anion

AlðOCðCF₃Þ₄whose volume can be estimated in various

ways. Firstly it could be estimated using Hofmann vol-

umes, whereupon VAlðOCðCF₃Þ₄^ꢀÞ ꢄ V½Alꢂ ¼ V ðAlO₄

C₁₆F₃₆Þ ¼ 0:709 nm³. Alternatively referring to the study

mentioned in the supplementary material included with ref-

erence [14b] where we estimated V(NO(Al(OC(CF)₂Ph)₄

= 0.9825 nm³we can approximate that: V ðAlðOC

ðCF₃Þ₄^ꢀÞ ꢄ V½Alꢂ ¼ V ðNOðAlðOCðCFÞ₂PhÞ₄ꢀ V ðNO^þÞꢀ

20V ðCÞ þ 12V ð FÞ ꢀ 20V ðHÞ ¼ 0:728 nm³, averaging to

give V ðAlðOCðCF₃Þ₄^ꢀÞ ¼ 0:719 nm³. Combining this vol-

ume with, for example, the value V ð1ð SNSÞ²₂^þÞ ¼

0:375 nm³estimated above we can then (by additivity)

estimate.

V(1(SNS)₂(Al(OC(CF₃)₃)₄)₂= 0.375 + 2(0.719) = 1.813

nm³. Using Eq. (D) for 1:2 salt (one dication and two

monoanions, for which I = 3) we obtain the lattice poten-

tial energy for 1(SNS)₂(Al(OC(CF₃)₃)₄)₂as 1022 kJ mol^ꢀ1

.

2þ

1ð SNSÞ₂{¹³C obs.(calc. for 1ð SNSÞ²₂^þÞ: 189.9 (191.4),

U_pot(1(SNS)₂(SbF₆)₂) is calculated using V(1(SNS)₂-

(SbF₆)₂) = [V(1(SNS)₂(SbF₆)₂.SO₂)–V(SO₂)] = 0.587 ꢀ 0.047

= 0. 540 nm³in Eq. (D) taking the ionic strength factor to be

174.6 (176.1), 143.1 (155.8), 133.9 (136.6) and 1(SNS)⁺

{¹³C obs. (calc. for 1(SNS)⁺):190.4 (193.1), 175.6 (178.7),

170.5 (171.7), 144.3 (156.6), 142.5 (149.6), 136.3 (134.6),

122.5 (125.3), ꢁ111 (111.2), respectively). The relative ratio

I = 1/2[1 Æ (2)²+ 2 Æ (1)²] = 3 and giving 1349 kJ mol^ꢀ1

.

V(1(SNS)₂(SbF₆)₂) is close to the Hofmann estimate

V(C₈Cl₂O₂N₄S₂Sb₂F₁₂) = 0.513 nm³.

of 1(SNS)⁺and 1ðSNSÞ₂cycloaddition products was

2þ

Unknown formula unit volumes, V_m, for ionic salts, can

hence be estimated from volumes of analogous salts that

have the same chemical formula and identical charge states

(ie., lattice ionic strength factors, I, Eq. (D) [14c] or using

nþ

Hofmann’s volumes [14g] for the ions NðSNSÞ_n

.

The experimental sublimation energy of a compound

related to 1, chloranil (2,3,5,6-tetrachloro-1,4-benzoqui-

none), is 98.7 kJ mol^ꢀ1[26]. From our comparison of

related compounds, we estimate the replacement of two

chloro- substituents by two cyano- substituents (see

Table S1a and S1b in supplemental material for full

details) in chloranil provides an enthalpy of sublimation

for 1 as 110–120 kJ mol^ꢀ1.²This is expected to be higher

than chloranil, since 1 has a larger dipole moment (sub-

2

2þ

Fig. 2. Structure of 1ðSNSÞ₂

. Ellipsoids are drawn at the 50%

The substitution of one Cl atom by one –CN group increases the

enthalpy of sublimation by ꢁ5.5kJ mol^ꢀ1(See Table S1a, Entries 3 and 4)

while the substitution of four Cl atoms by four –CN groups results in an

increase of ꢁ18–41 kJ mol^ꢀ1(Table S1a, Entries 1,2, 10, 11). Therefore,

the increase in sublimation enthalpy for each substitution of one Cl atom

by one –CN group is ꢁ5–10 kJ mol^ꢀ1; hence the enthalpy of sublimation

for 1 is estimated as 110–120 kJ mol^ꢀ1. We will use the latter value

throughout, so that the resulting solid state thermodynamic estimates

from Born-Haber cycles will be a lower limit.

˚

probability level. Selected bond lengths (A) and angles (ꢁ): C1–O1

1.209(5), C4–O2 1.212(5), C2–C3 1.349(5), R1: C2–C7 1.476(6), C7–N1

1.308(6), N1–S1 1.612(4), S1–N2 1.580(4), S2–N2 1.611(5), C7–S2

1.745(4); R2: C3–C8 1.471(5), C8–N3 1.308(5), S3–N3 1.608(4), S3–N4

1.590(4), S4–N4 1.600(4), C8–S4 1.739(4). Selected angles (ꢁ): O1–C1–C2

120.4(4), O2–C4–C3 119.7(3), C2–C3–C8 125.6(4), C3–C2–C7 126.0(3),

and selected dihedral angles (ꢁ): C7–C2–C3–C8 11.8(7), O1–C1–C2–C7

7.3(6), O2–C4–C3–C8 12.5(6).

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

531

2þ

Fig. 3. The estimated relative energy diﬀerence for the three rotational isomers (A–C) for 1ðSNSÞ₂based on the gas phase (MPW1PW91/6-31G^*)

calculated energies³.

approximated from the integration of the ¹³C chemical

shifts of similar substituted carbons and were consistently

found to be ca. 1:2, even after most of the product

(1(SNS)₂(SbF₆)₂Æ SO₂) had crystallized or precipitated

from the solution. After 7 days all SNSSbF₆was consumed

(¹⁴N NMR), giving a mixture of products (the ratio of

3.2. Cycloaddition chemistry of SNS⁺with 3

The reverse electron demand cycloaddition of the Lewis

acid SNS⁺with multiple bonds that act as Lewis bases is

well established (the reaction rate is inversely proportional

to the diﬀerences in the energies of the LUMO(SNS⁺) and

the HOMO(triple bond)) [1,3a], and therefore the cycload-

dition of SNS⁺with 3 is expected to undergo a site selective

cycloaddition at one of the four nitrile functionalities

(HOMO), and not at the electron deﬁcient –C@C– bond

[28]. In refuxing SO₂solution, reaction of an excess of

SNSSbF₆(enough to aﬀord the tetra-cycloaddition prod-

uct) with 3 gave a mixture of the site selective cycloaddition

products (1:1, 1:2 and 1:3 cycloaddition products, IR),

which are less soluble, while the more soluble fraction con-

tained starting materials (3 and SNSSbF₆) and a small

amount of unidentiﬁed cycloaddition products (IR). The

mass balance did not ﬁt the quantitative formation of

3(SNS)₃(SbF₆)₃Æ SO₂. A small scale experiment, performed

at room temperature, gave colorless crystals of

3(SNS)₃(SbF₆)₃Æ SO₂in moderate yield (40% isolated yield

1ðSNSÞ₂and 1(SNS)⁺remained ꢁ2:1, ¹³C NMR) and a

2þ

yellow-orange precipitate, assumed to be 1(SNS)₂-

(SbF₆)₂Æ SO₂. Thus the reaction of SNSSbF₆and 1 gives

1(SNS)₂(SbF₆)₂in essentially quantitative yield, on an

NMR scale. On the other hand, the reaction of SNS[Al-

(OC(CF₃)₃)₄] with 1 in a 1:1 stiochiometric ratio (Eq.

(2)) followed by multinuclear NMR (¹³C, ¹⁴N, ¹⁹F, ²⁷Al)

resulted in the formation of only the monocycloaddition

product 1(SNS)⁺and unreacted

1

and SNS[A-

l(OC(CF₃)₃)₄] in solution after 3 weeks. An analogous reac-

tion of SNSSbF₆with the mono-nitrile 2 (Eq. (3)) provided

2(SNS)⁺in SO₂solution as conﬁrmed by ¹³C (obs. (calc.)

192.8(190.8), 177.3 (173.8), 173.3 (168.6), 162.5 (160.3),

142.3 (155.6), 141.7 (150.2), 113.7 (114.3), 67.8 (73.2))

and ¹⁴N NMR (Figure S21 and S22, respectively). Th_ꢀe

experimental ¹³C NMR resonances of 2(SNS)⁺(as SbF₆

salt) further simpliﬁes and conﬁrm the assignment of the

¹³C NMR resonances for the monocycloaddition product

based on

3

and Eq. (4). The structure of

3(SNS)₃(SbF₆)₃Æ SO₂was determined by X-ray crystallog-

raphy (Fig. 4, Section 3.3.2) and further characterized by

IR and Raman microscopy (Figures S5 and S9,

respectively).

1(SNS)⁺as the AlðOCðCF₃Þ Þ salt, and by comparison

ꢀ

3

4

with calculated NMR tensors.

SO₂

1 þ 2SNSSbF₆ꢁ 1ðSNSÞ₂ðSbF₆Þ₂

ð1Þ

3.3. X-ray crystallography

SO₂

1 þ SNS½AlðOCð CF₃Þ₃Þ₄ꢂ ꢁ 1ð SNSÞ½AlðOCðCF₃Þ₃Þ₄ꢂ ð2Þ

SO₂

3.3.1. X-ray crystal structure of 1(SNS)₂(SbF₆)₂Æ SO₂

2 þ SNSSbF₆ꢁ 2ðSNSÞðSbF₆Þ

ð3Þ

ð4Þ

2þ

1ðSNSÞ₂given in Fig. 2, is the ﬁrst X-ray crystallo-

SO₂

graphic structure determination of an ortho bis-1,3,2,4-

dithiadiazolylium cation, and only the second example to

be prepared and characterized (cf. 7ðSNSÞ₂^2þ) [8]. In the

solid state, the dications are well separated from each other

and make a number of weak contacts with six surrounding

3 þ 3ðSNSSbF₆Þ ꢁ 3ðSNSÞ₃ðSbF₆Þ₃

3

Both rotational isomers B and C optimize in the gas-phase to give

rotational isomer A when no symmetry constraints are imposed (all other

symmetries, C_sor C₂are 2nd order or higher saddle points, by frequency

analysis). We choose the following criteria to evaluate the relative energy

diﬀerence between rotational isomers A–C (shown in Fig. 2): The ﬁrst

structure in the optimization steps to achieve the bond lengths, which are

within 60% of the sum of the two ‘‘observed’’ mean van der Waals radii

ꢀ

SbF₆anions (structural parameters of SbF₆anion given

in Figures S11 and S13 in the supplemental material). S^d+

–

F^dꢀcontacts fall in the range 2.986(3)–3.466(5) A. The

˚

molecules of SO₂(d(S–O) = 1.405(4) and 1.415(4) A, \O–

S–O = 118.3(3)ꢁ) are shorter than those found in the gas-

˚

for the respective atom, (cf. C–C £ 1.50 A, C–Cl £ 1.75 A, C–N £ 1.30 A,

˚

phase (d(S–O) = 1.431(2) A, \O–S–O = 118.5(10)ꢁ) [29]

˚

C–O £ 1.24 A, C–S £ 1.75 A, S–N £ 1.70 A) as visualized in ChemCraft

Version 1.5 [17a].

˚

and the solid state (d(S–O) = 1.4297(4) A, \O–S–

532

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

O = 117.5(1)ꢁ) [17b] (i) and numerous known examples of

SO₂of solvation [17d] that is likely due to a combination

of libration/rotation and other solid state eﬀects. The

SO₂molecules form several weak contacts S^d+–O^dꢀwith

the two –CNSNS rings (falling in the range 3.046 (4)–

˚

3.496 (4) A, Figure S12, supplemental material) [30].

The intra-dicationic bond distances and angles of the

chemically equivalent bonds are in agreement with previ-

ously reported data for related 1,3,2,4-dithiadiazolylium

(DTDA) salts (See Table S3a) [3b,3e,6a,9a,9b]. The orien-

tation of the two –CNSNS⁺rings relative to one another is

unique, considering the possible rotational isomers A–C

(Fig. 3) and comparison to previous examples where the

S^d+–N^dꢀelectrostatic interaction is predominant [9]. In

the gas-phase, the calculated structure (MPW1PW91/6-

31G^*) of rotomer A is the most energetically favorable of

the three potential rotomers (Fig. 3) and is similar to the

observed X-ray crystal structure (Fig. 2), in which the rel-

ative orientation of the –CNSNS⁺rings is mainly governed

by electrostatics (Table S7 in supplemental material).⁴Both

rotomers B and C revert to rotomer A when optimized in

the gas phase (MPW1PW91/6-31G^*). The electrostatic

interactions S^d+–O^dꢀbetween the –CNSNS⁺rings and

3þ

Fig. 4. Structure of 3ðSNSÞ₃

. Ellipsoids are drawn at the 50%

˚

probability level. Selected bond lengths (A): C1–C2 1.347(5), C6–N16

1.142(5); R1: C4–S8 1.752(3), S8–N9 1.593(3), N9–S10 1.582(3), S10–N11

1.606(3), C4–N11 1.305(5); R2: C3–S4 1.731(4), S4–N5 1.606(3), N5–S6

1.573(4), S6–N7 1.608(3), C3–N7 1.299(4); R3: C5–S12 1.735(4), S12–N13

1.596(3), S14–N13 1.584(3), S14–N15 1.610(3), C5–N15 1.297(4); Selected

angles (ꢁ): C3–C1–C4 114.1(3), C2–C1–C3 121.7(3), C1–C2–C5 123.5(3),

C2–C6–N16 175.6(4).

2þ

the C@O fragment in 1ðSNSÞ₂leads to dihedral angles

of 19.2 and 36.3ꢁ, respectively, between the quinoidal ring

and rings R1 and R2 (Fig. 2). The energetics of the related

12ðSNSÞ₂and its’ related isomers found the S^d+–O^dꢀ

2þ

interaction to be preferred in the gas phase, and have been

recently discussed [10].

3.7ꢁ between the ring R1 and the two central sp²C₁and C₂

atoms and nitrile) in Fig. 4. The dihedral angles between

the rings R2 and R3 and the C₆–C₂–C₁plane are 92.4ꢁ

and 37.7ꢁ, respectively (Fig. 4). The deviation from planar-

ity of 3ðSNSÞ₃^3þarise from repulsive electrostatic N^dꢀ–N^dꢀ

interactions and steric hinderance between the R2 and R3

rings, notwithstanding the favorable S^d+(R2) and N^dꢀ

(R3) interaction. This arrangement of the rings is diﬀerent

2þ

The quinoidal ring of 1ðSNSÞ₂(Fig. 2) adopts a shal-

low twisted chair conformation (greatest deviation for pla-

˚

narity is 0.063 0.004 A), while the bond lengths are

similar to that of 1 [31], with the exception of the C2–C7

and C3–C8 bond lengths which are 1.429(4) and 1.442(4)

in 1 and 1.476(6) A and 1.472(5) A in 1ðSNSÞ₂^2þ, reﬂecting

˚

3þ

an increase in the covalent radius of C₇and C₈from sp in 1

from that of the more symmetric 4ðSNSÞ₃[9a], where the

to sp²in 1ðSNSÞ₂

.

–CNSNS⁺rings are oriented such that the favorable elec-

trostatic S^d+–N^dꢀinteractions are maximized (see Scheme

2, Ref. [9a]).

2þ

3.3.2. Crystal structure of 3(SNS)₃(SbF₆)₃Æ SO₂

3þ

The X-ray crystal structure of 3ðSNSÞ₃(Fig. 4) is the

Two isomers (A and B) of 3ðSNSÞ₃are found to be

ﬁrst tri-cationic tris-1, 3, 2, 4-dithiadiazolylium salt to be

structurally characterized (the structural parameters of

minima in the gas phase, both lower in energy than isomer

C observed in the solid state (Fig. 5). Isomer A is the lowest

energy structure in the gas-phase, however the energies of

the S^d+–N^dꢀelectrostatic interactions of isomers A and C

are comparable, based on the simple point charge model,

Eq. (C) (See Table S7b for details) [25a]. Not surprisingly,

isomer C found in the solid state has a similar, essentially

co-planar, trans arrangement of rings R1 and R3 observed

in isomer A. There are weak but numerous, S^d+– F^dꢀcat-

ꢀ

the SbF₆anion are given in the supplemental material,

Figures S14–16). The chemically equivalent bond lengths

and angles of the –CNSNS⁺rings in 3ðSNSÞ₃are similar

3þ

to those previously reported for other 1,3,2,4-dithiadiazol-

ylium salts (See Table S3a) [3b,3e,6a,9a,9b]. The free nitrile

and the –CNSNS⁺moiety (R1, Fig. 4) are sterically non-

hindered, and lie almost in the same plane (dihedral angle,

ꢀ

ion-anion interactions from the 10 neighbouring SbF₆

˚

anions, falling in the range 2.705(3)–3.461(3) A and only

An estimation of the attractive and repulsive energies of the electro-

one very weak S^d+–N^dꢀinteraction, (2.991(3) A) between

4

the free nitrile and a neighboring 3ðSNSÞ₃^3þ. The crystal

structure of 3(SNS)₃(SbF₆)₃Æ SO₂contains one SO₂

static interactions based on a simple point charge model (see Section 2.7)

[25a] were calculated to compare the relative diﬀerence between the S^d+

–

O^dꢀinteraction and more common S^d+–N^dꢀinteraction [9a]. The S^d+–O^dꢀ

˚

molecule (d(S–O) = 1.424(3) and 1.413(3) A, \O–S–O =

interaction (6210 kJ mol^ꢀ1

)

is more favorable than the S^d+–N^dꢀ

(6160 kJ mol^ꢀ1) interaction, while the repulsive S^d+–S^d+(6231 kJ mol^ꢀ1

)

117.3(2)ꢁ, cf. gas-phase, d(S–O) = 1.431(2) A, \O–S–O =

˚

is highly unfavorable (Table S7, supplemental material).

118.5(10)ꢁ [29] and solid state, d(S–O) = 1.4297(4) A,

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

533

Fig. 5. The optimized gas-phase conformation of isomers A and B and the conformation corresponding to the actual X-ray structure, isomer C of

3þ

3ðSNSÞ₃(the latter was a single point calculation).

Scheme 1.

\O–S–O = 117.5(1)ꢁ [17b,17c,17d]) of solvation, which is

ever, the site selective cycloaddition of SNS⁺with 1

occurs at the nitrile functionalities exclusively. This is in

accordance with previous results which showed that reac-

tions of C@O and X₂–C@C–X₂(X = F, Cl) with SNS⁺

were likely thermodynamically and kinetically unfavor-

able [33].⁵

However, the reverse electron demand cycloaddition of

SNS⁺with 1 (LUMO(SNS⁺)–HOMO (C„N)) does not

appear to proceed through the HOMO–LUMO interaction

as found previously for other nitriles, since the HOMO

coordinated to both -CNSNS R2 and R3 rings (S^d+–O^dꢀ

˚

,

3.073(3) and 3.113(4) A) in a bridging motif (Figure S15,

supplemental material). The S^d+–F^dꢀand the S^d+–O^dꢀ

interactions from the SO₂molecules may account for the

small distortion of isomer C from that of isomer A, calcu-

lated as the most stable conformation in the gas phase.

3.4. Energetics of the cycloaddition of SNS⁺with nitriles

3.4.1. Site selective cycloaddition of SNSSbF₆to 1

The site selective cycloaddition of SNS⁺at the nitrile

5

On the bas_þis of

a simpliﬁcation of Klopman’s equation,

functionality of

1

is thermodynamically preferred

DE_MO¼ ½LUMO_SNSꢀ HOMO_ABꢂ^ꢀ1(AB = unsaturated bond (ie. C@C,

(>160 kJ mol^ꢀ1in gas-phase and solution) relative to the

other four unsaturated centers (two C@O and two C@C

bonds), see Scheme 1 and Table 2 (entries 5–7). Typical

1,3-dipoles (e.g., diazoalkanes, nitrones) undergo cycload-

dition reactions with quinones at the –C@C– bond or the

C@O moieties [28]. The most common site of cycloaddi-

tion in 1 is at the NC–C@C–CN double bond [32]. How-

C„C, C„N)) found the kinetic barriers should be small (E_kinetic

a

(E_MO)

^ꢀ1). However, a charge term (DE_CH) and for the electrophilic CF₂–

C@C–CF₂is dominant, and the reaction is kinetically unfavorable

ðDE⁰_MO¼ DE_MOþ DE_CHÞ. A simple thermodynamic model of bonds

formed minus bonds broken suggested the reactions were possibly

thermodynamically unfavorable. Moreover, the reaction of SNS⁺with a

variety of R₂C@O (R = F,CH₃, ^tBu,CF(CF₃)₂and X₂C–C@C–CX₂

(X = F,Cl) did not occur experimentally.

534

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

Fig. 6. Atomic orbital coeﬃcients of HOMO and HOMO-2 of 1 calculated at the MPW1PW91/6-31G^*level of theory. Mulliken charges are given in

brackets.

(MO 56, E = ꢀ0.3191 a.u.) of 1 is largely located on the

Cl–C@C–Cl portion of 1 (Fig. 6). Instead, the reaction is

most likely to proceed by donation of electron density from

a lower lying ﬁlled molecular orbital of 1 (HOMO-2; MO

54, E = ꢀ0.3474 a.u.) of correct symmetry into the LUMO

of SNS⁺. This discrepancy can be rationalized given the

larger atomic coeﬃcients of the HOMO-2 at the nitrogen

atoms (0.261 versus 0.103 a.u. of the HOMO), because

the large coeﬃcients aids the more pronounced charge

transfer to the LUMO of SNS⁺.

The proximity of the electronegative oxygen to the

nitrile group may provide an ideal in-plane electrostatic

interaction that facilitates the cycloaddition of SNS⁺with

the nitrile functionality (–CN), similar to that proposed

for the electrostatic interaction of SNS⁺with the nitrogen

in the 4-position of the 1,3,2,4-dithiadiazolium ring

[9a,9b]. Kinetic factors involving atomic orbital coeﬃ-

cients, charges, and steric interactions have previously

been suggested to account for the formation of a number

of di- and tri-cycloaddition products of SNSMF₆

(M = As, Sb) with the corresponding nitriles [3a,3f],

despite the expectation that additional cycloadditions

would become increasingly less kinetically favorable.

However, experimentally these reactions typically proceed

to give the multiple cycloaddition products in essentially

quantitative yield [5e,8,9].

few crystals of 11(SNS)⁺were obtained and the X-ray

crystal structure determined [10]. This implies that under

certain conditions (e.g., using a large excess of dinitrile)

the mono-cycloaddition product could be isolated as the

predominate product.⁶We note that attempts to prepare

mono- cycloaddition product, 6(SNS)⁺, from SNS⁺and

a 10-fold excess of 6 were unsuccessful and yielded the

2þ

di- cycloaddition, 6ðSNSÞ₂in 97% yield (Table 3). This

observation was originally explained by kinetic factors

[3f,9b], but more recently, we account for this observation

by the gain in lattice enthalpy of the 1:2 salts relative to

twice that of the 1:1 salts and the low solubility of the

di-cycloaddition product, 6(SNS)₂(AsF₆)₂in SO₂. Thus,

given_ꢀthe similarity in ionic volumes for the anions

ꢀ

AsF₆ðV ¼ 0:110 nm³)

and

SbF₆ðV ¼ 0:121 nm³),

Fig. 2, and the solubility of their respective salts, similar

trends are expected to be observed for both salts.

3.4.2. Thermodynamic estimates of the cycloaddition of

SNSSbF₆with 1 and 3

In order to determine the relative trends in the reactivity

of these systems we investigated the thermodynamics in the

gas phase, solution (SO₂and CH₂Cl₂) and solid state

(Table 2). The ﬁrst cycloaddition of SNS⁺to 1 is favorable

in the gas-phase (Table 2, Entry 1, ꢀ159 kJ mol^ꢀ1), while

the second is unfavorable (Table 2, Entry 2,

+109 kJ mol^ꢀ1). In SO₂solution both the ﬁrst and second

cycloaddition of SNS⁺with 1 are favorable by ꢀ103 and

ꢀ63 kJ mol^ꢀ1, respectively, with similar values obtained

for CH₂Cl₂(Table 2). The free energies (DG) in SO₂solu-

tion also indicate that both the ﬁrst and second cycloaddi-

tion should be favorable, in accordance with the observed

experimental results (NMR, see Section 3.1) in solution.

However, the situation in CH₂Cl₂solution may only favor

the ﬁrst cycloaddition since DG for the second cycloaddi-

tion is +1 kJ mol^ꢀ1(see Table 2, Entry 1).

Recently, the cycloaddition reaction of SNSMF₆

(M = As, Sb) with 11 and 12 has been shown to predom-

inantly give the corresponding dicycloaddition products

2þ

11ðSNSÞ₂and 12ðSNSÞ₂^2þ, respectively [10]. It was sug-

gested that the reactions were under thermodynamic

rather than kinetic control, since no preference for the

second cycloaddition was found when the transition states

were examined in the gas-phase by DFT quantum chem-

ical calculations, although experimentally kinetic factors

were not completely ruled out. Similar to the reaction

of 1 and two equivalents of SNS⁺reported herein,

mixtures of both mono- (e.g., 11(SNS)⁺and 12(SNS)⁺)

6

In the case of the cycloaddition of one equivalent of SNSSbF₆with a

2þ

and di-cycloaddition products (e.g., 11ðSNSÞ₂

and

four fold excess of the dinitrile NC–C₄F₈–CN (kinetic conditions) the

monocycloaddition product (NC–C₄F₈–CNSNS) was isolated in good

yield. K.V. Shuvaev and J. Passmore, unpublished results.

12ðSNSÞ₂were observed by ¹³C NMR, but could not

2þ

be separated and isolated. However, in the case of 11, a

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

535

Table 3

Compilation of experimental results for the cycloaddition of SNSMF₆(M = As, Sb) with multifunctional nitriles (Chart 1)

Compound^a

Apparent reaction time

Temperature (ꢁC)

Yield (%)

Identiﬁcation/characterization^b,^c

Reference

2þ

3þ

1ðSNSÞ

7 d

60

25

45

50

25

60

85

44

72

59

84

96

76

97

75

85

92

70

N/A^f

74

90

EA, IR, Raman, NMR, X-ray

IR, Raman, X-ray

EA, IR, CV, NMR, MS, X-ray

EA, IR, CV

EA, IR, UV-Vis, CV, X-ray

IR, NMR, X-ray

EA, IR, NMR, X-ray

EA, IR, Raman, NMR, MS, X-ray

EA, IR, NMR

EA, IR, CV, NMR, MS, X-ray

EA, IR, NMR

NMR, Raman, IR, X-ray

EA, IR, Raman, NMR, X-ray

IR, NMR, X-ray

this work

[9a]

3ðSNSÞ²₃

12 d

1.5 h

16 h

20 h

10 w

5 d

18 h

5 d

4(SNS)

þ

4ðSNSÞ

4ðSNSÞ²₃

2þ

5(SNS)⁺

[9b]

2þ

5ðSNSÞ

[9b,3f]

[9b]^d, [3f]

[8]

[5e]

[10]

6ðSNSÞ²

2þ

7ðSNSÞ²

8ðSNSÞ²

9ðSNSÞ²₂

e

3þ

10ðSNSÞ₃

11(SNS)⁺

3 w

2 w

3 d

2þ

11ðSNSÞ₂

12(SNS)^+g

a

The AsF^ꢀ₆salt unless otherwise noted.

b

c

d

e

f

Some abbreviations: EA = elemental analysis, CV = cyclic voltammetry, MS = mass spectrum.

¹H and/or, ¹³C and/or, ¹⁴N NMR.

Trace of 1:1 monocycloaddition product might have been present, IR.

ꢀ

Other salts prepared included for 9ðSNSÞ₂^2þ: Cl , Br , S₃N₂and SbCl₆^ꢀand for 10ðSNSÞ₃the Cl^ꢀsalt.

ꢀ

3þ

Only a few crystals isolated and identiﬁed by X-ray crystallography, while in solution the 1:1 product is identiﬁed by ¹³C- and ¹⁴N NMR.

g

The SbF^ꢀ₆salt was prepared; Also, the 1:1 product was identiﬁed in solution by ¹³C-and ¹⁴N NMR.

SO₂

1ðSNSÞ^þꢁ SNS^þþ 1

ð5Þ

ð6Þ

3.4.3. Thermodynamics estimates of the cycloaddition of

SNS[Al(OC(CF₃)₃)₄] with 1 and kinetic considerations

By the VBT estimates the formation of the 1:1 cycload-

dition product containing the large (V = 0.758 nm³) weakly

SO₂

1ðSNSÞ^þþ 1ð SNSÞ^þꢁ 1ð SNSÞ²₂^þþ 1

ꢀ

In both the gas-phase and solution (SO₂and CH₂Cl₂)

the monocycloaddition product 1(SNS)⁺is stable with

respect to dissociation to SNS⁺and 1 (Eq. (5)) and dis-

proportionation to 1ðSNSÞ₂and 1 (Eq. (6)). The situa-

coordinating anion AlðOCðCF₃Þ₃Þ is favorable in the

4

solid state (DH_rxn= ꢀ17 kJ mol^ꢀ1; see Table 2, Entry 1).

However, the second cycloaddition in SO₂solution is

favorable (Table 2, Entry 1), and therefore the 1:2 cycload-

2þ

tion is reversed in the solid state where the diﬀerence

between the lattice enthalpy gain for the resulting 1:2 salt

1(SNS)₂(SbF₆)₂(U_pot= 1322 kJ mol^ꢀ1) and the 1:1 salt

for 1(SNS)(SbF₆) (U_pot= 419 kJ mol^ꢀ1· 2) exceeds the

unfavorable gas-phase term for the second cycloaddition

(see Table 2, Entry 2). Therefore, in the solid state the

disproportionation reaction according to Eq. (6) is ther-

modynamically favored (ca. ꢀ335 kJ mol^ꢀ1; see Table 2,

Entry 4).

dition product, 1ðSNSÞ₂should also be observable in

solution. Yet, experimentally only the 1:1 cycloaddition

product, 1(SNS)⁺is observed, although the 1:2 product

could be present, but still not observed by ¹³C NMR if in

low concentration. Furthermore, reaction (Eq. (2)) at

40 ꢁC for 16 days in SO₂solution had little eﬀect on the

nature of the reaction products (little change in the relative

ratio of the integrations in the ¹⁴N NMR for the peaks of

1(SNS)⁺, 1 and SNS⁺, in the time frame of 4–16 days). This

suggests that _ꢀthere might be ion pairing between

AlðOCðCF₃Þ Þ and SNS⁺, which has previously been

In the case of 3, only the ﬁrst cycloaddition is favorable

in the gas-phase, while in SO₂solution the ﬁrst three cyc-

3

4

loadditions are favorable (ꢀ82, ꢀ71, ꢀ117 kJ mol^ꢀ1

,

suggested for the SbCl₆and AlCl₄salts of SNS⁺, both

of which failed to undergo clean cycloaddition chemistries

[35]. Tight ion pair formation has been suggested [36] in the

ꢀ

respectively, Table 2, Entries 9–11). The lattice potential

energy for 3(SNS)₃(SbF₆)₃must be large (U_pot

P

ꢀ2100 kJ mol^ꢀ1) to overcome the sum of the gas-phase

terms for each of the three cycloadditions (+410 kJ mol^ꢀ1),

heat of sublimation of 3 (+82 kJ mol^ꢀ1) [34] and three

times the lattice enthalpy of SNSSbF₆(ꢀ525 kJ mol^ꢀ1).

The formation of the 1:1 salt, 3(SNS)(SbF₆), is unfavor-

able in the solid state with respect to 3 and SNSSbF₆

(+65 kJ mol^ꢀ1, Table 2, Entry 9). The disproportionation

of two 3(SNS)(SbF₆) to 3(SNS)₂(SbF₆)₂and 3 is favorable

(ꢀ269 kJ mol^ꢀ1, Table 2, Entry 13) largely due to the gain

in the lattice potential energy of the 1:2 salt with respect

to twice that of the 1:1 salt. This is similar to the energetics

of 1.

observed decomposition of the AlðOCðCF₃Þ₃Þ ^ꢀanion with

4

highly electrophilic species, e.g., P₂I₃^þ. Ion-pair formation

could decrease the rate of reaction of the cycloaddition

reaction (a kinetic eﬀect) and also aﬀect the free energies

(DG) of the second cycloaddition in solution. Our estimates

of the thermodynamics imply that formation of

1ðSNSÞ₂½AlðOCðCF₃Þ₃Þ ^ꢀꢂ₂is also favorable in the solid

4

state, but surprisingly, this product was not observed.

1ð SNSÞ₂½AlðOCðCF₃Þ₃Þ ^ꢀꢂ₂, if formed, would likely be

4

very soluble, in contrast to 1(SNS)₂(SbF₆)₂Æ SO₂, which

is only moderately soluble in SO₂solution. Thus removal

2þ

of 1ðSNSÞ₂from the solution drives the equilibrium,

536

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

(Eq. (1)) to the right side in the case of SbF₆^ꢀ. Alterna-

tively, it is also possible that the estima_ꢀtes of lattice poten-

investigated experimentally [5e,6,8,9] and a compilation

of experimental results are given in Table 3. The corre-

sponding thermodynamic estimates are given in Table 4.

In these experiments, it was observed that the cycloaddi-

tion of SNSMF₆(M = As, Sb) with compounds containing

two or more unsaturated centers results in the transforma-

tion of every nitrile group into a 1,3,2,4-dithiadiazolylium

moiety without identiﬁcation of the intermediate 1:1 cyclo-

addition products (Table 4). Only three known cases have

been reported where the intermediate 1:1 cycloaddition

product have been identiﬁed or isolated in the solid state

[9,10]. Based on our thermodynamic approach, we show

that the ﬁrst cycloaddition is favorable in the gas-phase

in all cases for the multifunctional nitriles 4–10, while the

second is unfavorable in the gas-phase [37] (for tricyano-

methide (CðCNÞ₃^ꢀ, 4, the unfavorable tri-cycloaddition

product is 4ðSNSÞ²₃^þ) [9a], Table 4. In solution, the

enthalpy (DH) and free energy changes (DG) for both the

tial energies of the 1:2 AlðOCðCF₃Þ₃Þ salts by the VBT

4

equations with the current parameters of Jenkins et al

may not be appropriate and may need further ﬁne tuning

ꢀ

to ﬁt salts of very large anions (like AlðOCðCF₃Þ₃Þ as

4

well as dications containing separated positive charge cen-

ters (i.e., large spacer group). We also note that as far as we

are aware, no 1:2 salts ðDication½AlðOR_fÞ₄^ꢀꢂ₂, where

R_f= CH(CF₃)₂, C(CF₃)₃, C(CF₃)₂(C₆F₅)) have yet been

reported in the literature [37b].

3.4.4. Accounting for the experimental observations for the

cycloaddition of SNSMF₆(M = As, Sb) with other

multifunctional nitriles

We have also estimated the energies of the reactions of

SNS⁺in the gas phase, solution and solid phase, for the

multifunctional nitriles shown in Chart 1 that have been

Table 4

Calculated gas-phase and solution enthalpies (DH), solution Gibbs free energies (DG) and solid state estimates for multifunctional nitriles, 4–10 (Chart 1)

Entry From Chart 1

Gas

phase^a

X^ꢀ¼ ½SbF₆^ꢀꢂ solid

X^ꢀ= [Al]^ꢀsolid

SO₂solution

DH

DH^b

DH

DG^c

1

2

[4] (g) + SNS⁺(g) ! 4(SNS) (g)

ꢀ578

ꢀ795

ꢀ556 ꢀ136

ꢀ222 ꢀ98

d

½4ꢂ ðgÞ þ 2SNS^þðgÞ ! 4ðSNSÞ₂ðgÞ

þ

K[4] (s) + 2 SNSX (s) ! 4(SNS)₂X (s) + KX

ꢀ148

ꢀ168

(s)

3

4ðSNSÞ₂^þðgÞ þ SNS^þðgÞ ! 4ðSNSÞ₃^2þðgÞ

4(SNS)₂X (s) + SNSX (s) ! 4 (SNS)₃(X)₂(s)

5 (g) + SNS⁺(g) ! 5(SNS)⁺(g)

+51

ꢀ124 ꢀ79

ꢀ243 ꢀ206

ꢀ868

ꢀ165

ꢀ252

ꢀ19

ꢀ270

+5

ꢀ637

ꢀ197

ꢀ156

ꢀ48

4

ꢀ246

+178

ꢀ75

5 (s) + SNSX (s) ! 5(SNS)X (s)

5

5ðSNSÞ^þðgÞ þ SNS^þðgÞ ! 5ðSNSÞ₂^2þðgÞ

5(SNS)X (s) + SNSX (s) ! 5(SNS)₂(X)₂(s)

6(g) + SNS⁺(g) ! 6(SNS)⁺(g)

ꢀ64

ꢀ74

ꢀ78

ꢀ91

ꢀ60

ꢀ96

ꢀ85

ꢀ97

ꢀ83

ꢀ90

ꢀ76

ꢀ60

ꢀ14

ꢀ36

ꢀ50

ꢀ23

ꢀ57

ꢀ46

ꢀ57

ꢀ44

ꢀ52

ꢀ38

ꢀ28

6

6 (s) + SNSX (s) ! 6(SNS)X (s)

7

6ðSNSÞ^þðgÞ þ SNS^þðgÞ ! 6ðSNSÞ₂^2þðgÞ

6(SNS)X (s) + SNSX (s) ! 6(SNS)₂(X)₂(s)

7(g) + SNS⁺(g) ! 7(SNS)⁺(g)

+165

ꢀ153

+93

ꢀ172

ꢀ52

8

7 (s) + SNSX (s) ! 7(SNS)X (s)

9

7ðSNSÞ^þðgÞ þ SNS^þðgÞ ! 7ðSNSÞ₂^2þðgÞ

7(SNS)X (s) + SNSX (s) ! 7(SNS)₂(X)₂(s)

8 (g) + SNS⁺(g) ! 8(SNS)⁺(g)

ꢀ315

+9

ꢀ240

ꢀ48

10

11

12

13

14

15

ꢀ152

+50

8 (s) + SNSX (s) ! 8(SNS)X (s)

8ðSNSÞ^þðgÞ þ SNS^þðgÞ ! 8ðSNSÞ₂^2þðgÞ

8(SNS)X (s) + SNSX (s) ! 8(SNS)₂(X)₂(s)

9 (g) + SNS⁺(g) ! 9(SNS)⁺(g)

ꢀ358

+1

ꢀ283

ꢀ56

ꢀ160

+55

9 (s) + SNSX (s) ! 9(SNS)X (s)

9ðSNSÞ^þðgÞ þ SNS^þðgÞ ! 9ðSNSÞ₂^2þðgÞ

9(SNS)X (s) + SNSX (s) ! 9(SNS)₂(X)₂(s)

10 (g) + SNS⁺(g) ! 10(SNS)⁺(g)

ꢀ353

ꢀ278

ꢀ137

Enthalpy of sublimation of 10

not known

10ðSNSÞ^þðrmgÞ þ SNS^þðgÞ ! 10ðSNSÞ₂^2þðgÞ +78

10(SNS)X (s) + SNSX (s) ! 10(SNS)₂(X)₂(s)

ꢀ323

ꢀ254

þ

3þ

16

a

10ðSNSÞ₂^2þþ SNS ! 10ðSNSÞ₃

+266

Includes zero point energy (ZPE) correction.

Calculated from appropriate Born-Haber cycles, using the calculated gas phase values and the volume based thermodynamic (VBT) estimates of the

b

lattice potential energies (see supplemental material for full details).

c

Including thermal correction to Gibbs free energy taken from the MPW1PW91/6-31G^*(gas-phase) frequency calculations.

d

The solid state thermodynamics are based on the lattice enthalpy estimates (VBT method) where U_pot[K(C(CN)₃] = 608 kJ mol^ꢀ1

,

U_pot[KSbF₆] = 567 kJ mol^ꢀ1, U_pot[K[Al]] = 364 kJ mol^ꢀ1

.

A. Decken et al. / Inorganica Chimica Acta 361 (2008) 521–539

537

ﬁrst and second cycloaddition are negative, implying the

reactions are favorable, while in the solid state, the gain

in lattice enthalpy for the resulting 1:2 salt (dication and

two mono-anions) compared to twice that of the 1:1 salt

(mono-cation and mono-anion), is greater than the unfa-

vorable gas-phase term [14]. Therefore, the situation for

the other nitriles in all three phases is similar to that of 1

and 3 when SNSMF₆(M = As, Sb) is used.

(OC(CF₃)₃)₄) in solution, and the predicted stabi_ꢀlity of

the 1:1 salt in the solid state, in contrast to the SbF₆case,

is an encouraging result which should allow the prepara-

tion of other 1:1 cycloaddition products with a free –CN

moiety. Subsequent reduction of the monocycloaddition

products would potentially provide access too new mono-

radicals of current interest and is currently under investiga-

tion. Ion-pair_ꢀformation between SNS⁺and the

While the nature of the substituents (electron-withdraw-

ing or donating) and size of the substituent and spacer

groups aﬀect the heats of vaporization and lattice enthalpy,

they only slightly change the values of the reaction

enthalpy (DH) for SNS⁺with multifunctional nitriles in

the solid state, but not the general trend. The substituents

(electron-withdrawing or donating) may also aﬀect the

kinetics of the reverse electron demand cycloaddition reac-

tion of SNS⁺, but in general the starting materials and the

monocycloaddition products are typically soluble, while

AlðOCðCF₃Þ₃Þ anion has been suggested to explain the

4

inconsistency with our simple thermodynamic model,

which predicted the 1:2 cycloaddition product, 1(SNS)₂[Al-

(OC(CF₃)₃)₄]₂, to be stable in solution and the solid state,

however, 1(SNS)₂[Al(OC(CF₃)₃)₄]₂, was not experimentally

observed. Further investigation of the cycloaddition

chemistry of SNS[Al(OC(CF₃)₃)₄] is necessary to access

the potential of this new SNS⁺salt.

5. Supplemental material

ꢀ

MF₆(M = As, Sb) salts of the dicycloaddition products

are moderately to sparingly soluble. Thus, the dicycloaddi-

tion product, once formed, precipitates out of solution,

shifting the equilibrium in solution towards the thermody-

namically favored dicycloaddition product.

Optimized geometries as atomic coordinates (x,y,z) and

total energies for all calculated molecules in gas-phase and

solution. Details of electrostatic and thermodynamic esti-

mates, calculated GIAO tensors, FT-IR and Raman spec-

tra. Structural parameters for the 1(SNS)₂(SbF₆)₂Æ SO₂

and 3(SNS)₃(SbF₆)₃Æ SO₂.

4. Conclusion

All multinuclear NMR (¹³C, ¹⁴N, ¹⁹F, ²⁷Al), FT-IR and

Raman spectra and supporting details.

We have demonstrated that the cycloaddition chemistry

of SNSSbF₆with 1 and 3 is synthetically useful in the prep-

aration of sulfur–nitrogen heterocyclic rings that are not

readily available by other synthetic routes. The observed

preference for the di- and tri-cycloaddition product can

be rationalized by means of the DFT calculations in both

the gas-phase and solution and the volume based thermo-

dynamic (VBT) approach [14]. These simple thermody-

namic models are useful in understanding of the

experimental ﬁndings, as well as identifying future syn-

thetic targets of interest.

Acknowledgments

J.P. thanks Professor Anthony Downs for the memora-

ble stay in his lab during a sabbatical leave and Jesus Col-

lege Oxford for the 1996/97 Visiting Senior Research

Fellowship. During this time a meeting with Don Jenkins

subsequently led to development of the ‘volume based ther-

modynamic’ derivation of lattice enthalpies and other ther-

modynamic quantities that are successfully applied in this

paper (Ref. [14] and http://www.warwick.ac.uk/go/ther-

mochemistry/).

We thank the Natural Sciences and Engineering Re-

search Council (NSERC) of Canada and University of

New Brunswick for ﬁnancial support. We would like to

thank Dr. Carsten Knapp, Dr. Mikko Rautainen, for help-

ful discussions and Ms. Maria Correia for help with the

experimental work.

The 1:2 cycloaddition product of SNSSbF₆with 1 pro-

vides access to a new class of hybrid quinoidal-thiazyl sys-

tems, which can potentially serve as electron acceptors for

charge transfer complexes and redox reactions. The readily

reducible 1,3,2,4-dithiadiazolylium cations and quinoidal

ring potentially provide access to a variety of oxidation

states, which are mixed organic main group radicals that

on their own may have interesting conductive and magnetic

properties. These compounds are also of interest in the

coordination chemistry of transition metals, e.g, as possible

hybrid magnetic materials. Furthermore, the preparation

Appendix A. Supplementary material

of the tri-cycloaddition product 3ðSbF₆Þ₃from SNS⁺

3þ

Supplementary data associated with this article can be

found, in the online version, at doi:10.1016/j.ica.

2007.05.033.

and 3 provided access to this very strong electron acceptor,

which is a particularly interesting precursor for charge

transfer complexes with interesting physical properties.

The ﬁrst synthetic application of the cycloaddition

chemistry of _ꢀSNS⁺with the weakly coordinating

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