Concurring Chalcogen- and Halogen-Bonding Interactions in Supramolecular Polymers for Crystal Engineering Applications

Article abstract of DOI:10.1002/chem.201904762

The engineering of crystalline molecular solids through the simultaneous combination of distinctive non-covalent interactions is an important field of research, as it could allow chemist to prepare materials depicting multi-responsive properties. It is in this context that, pushed by a will to expand the chemical space of chalcogen-bonding interactions, a concept is put forward for which chalcogen- and halogen-bonding interactions can be used simultaneously to engineer multicomponent co-crystals. Through the rational design of crystallizable molecules, chalcogenazolo pyridine scaffold (CGP) modules were prepared that, bearing either a halogen-bond acceptor or donor at the 2-position, can interact with suitable complementary molecular modules undergoing formation of supramolecular polymers at the solid state. The recognition reliability of the CGP moiety to form chalcogen-bonded dimers allows the formation of heteromolecular supramolecular polymers through halogen-bonding interactions, as confirmed by single-crystal X-ray diffraction analysis.

Full text of DOI:10.1002/chem.201904762

A Journal of
Accepted Article
Title: Concurring Chalcogen- and halogen-bonding interactions in
supramolecular polymers for crystal engineering applications
Authors: Nicolas Biot and Davide Bonifazi
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To be cited as: Chem. Eur. J. 10.1002/chem.201904762
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10.1002/chem.201904762
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Chemistry An European Journal
- Full Paper –
Concurring chalcogen- and halogen-bonding
interactions in supramolecular polymers for crystal
engineering applications
Nicolas Biot and Davide Bonifazi*
[*] Nicolas Biot and Prof. Dr. D. Bonifazi
School of Chemistry; Cardiff University
Park Place, CF10 3AT, Cardiff, United Kingdom.
E-mail: BonifaziD@cardiff.ac.uk
[**]D.B. gratefully acknowledges Cardiff University and the EU
through the MSCA-RISE funding scheme (project INFUSION) for
the financial support. The authors also acknowledge the use
of the Advanced Computing (ARCCA) at Cardiff University, and
associated support services. The authors thank Dr. B. Kariuki
for the refinement of some crystal structures.
Keywords: halogen-bonding / chalcogen-bonding / SBIs / tellurium
/ selenium / crystal-engineering / supramolecular chemistry /
self-assembly / supramolecular polymers
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Abstract: The engineering of crystalline molecular solids
through the simultaneous combination of distinctive non-covalent
interactions is an important field of research as it could allow
chemist to prepare materials depicting multiresponsive
properties. It is in this contest that, pushed by our will to
expand the chemical space of chalcogen-bonding interactions
that, in this work we put forward the concept for which
chalcogen- and halogen-bonding interactions can be used
simultaneously to engineer multicomponent co-crystals. Through
the rational design of crystallizable molecules, we prepared
chalcogenazolo pyridine scaffold (CGP) modules that, bearing
either a halogen-bond acceptor or donor at the 2-position can
interact with suitable complementary molecular modules,
undergoing formation of supramolecular polymers at the solid
state. The recognition reliability of the CGP moiety to form
chalcogen-bonded dimers allow the formation heteromolecular
supramolecular polymers through halogen-bonding interactions as
confirmed by single-crystal X-ray diffraction analysis.
Figure to the table of content.
2
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Introduction
The primary aim of supramolecular chemistry is to link molecular
chemistry with the construction of thermodynamically-stable
architectures of higher complexity through the principle of
self-assembly using non-covalent interactions.[1] In this
respect, the possibility of simultaneously exploiting multiple
interactions[2] can allow chemists to engineer architectures with
multiresponsive properties.[3] For example, this is the case of
supramolecular polymers,[4] whose monomeric units hold together
via highly directional and reversible non-covalent interactions.
In a series of instances, it has been shown that multi-responsive
materials could be prepared when monomers displaying heterotopic
recognition units were used.[5] Another example is that of
molecular solids, the functional properties of which enabled
through the rational design of crystallizable molecular synthons
undergoing programmed non-covalent directional interactions.[6]
Typical examples describe the simultaneous of use of H-bonding
(HBIs) and metal-coordination interactions.[7]
Beside the classical interactions of the supramolecular
toolbox,[8] in the recent years chemists became interested in
secondary-bonding interactions (SBIs).[9] The Halogen-bonding
interaction (XBI) is the most renowned SBI,[6d, 9b, 10] and its use
has been validated in crystal engineering applications,[11] liquid
crystals,[12]
functional materials,[13]
and biochemistry.[14]
Structures containing electron-deficient chalcogen atoms can
also give rise to SBIs, known as chalcogen-bonding interactions
3
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(EBIs).[15] Recent investigations showed that chalcogen bonds
could be used to foster molecular organization in solids,[16]
anion recognition and transport,[17] catalysis,[18] biology[19] and
self-assembly.[20] While XBIs have been proven to be compatible
with HBIs both in crystals[21] and biological systems,[22] the
simultaneous expression of EBIs with other interactions has been
marginally studied.[23] Recent examples include the formation of
wire-like assemblies at the solid state of 1,4-
diiodotetrafluorobenzene (DITFB) with either 2,1,3-
benzoselenadiazole[23a] or diphenyl dichalcogenide.[23c] Ourselve,
we recently repored a heteromolecular polymeric chain, in which
the monomers are held together through EBIs and XBIs at the solid
state.[23b] It is in this context that herein we present a full
account on the rational engineering of multicomponent co-
crystals through the simultaneous expression of chalcogen- and
halogen-SBIs. Building on the recognition persistency of the
self-associating chalcogenazolo pyridine scaffold (CGP),[23b, 24]
in this work we describe a series of tailored ditopic molecular
modules that, through the formation of EBIs and XBIs,
crystallized into solids through the formation of programmed
heteromolecular supramolecular polymers.
Design of multi-component supramolecular polymers. In our
crystal-engineering approach, the idea is to prepare
supramolecular polymers at the solid state through a co-
crystallisation of two ditopic molecular modules: the chalcogen
(Ch) and halogen (Hal) modules, respectively (Scheme 1). While
4
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the Ch modules are heterotopic, i.e. bearing two diverse
recognition groups, the Hal synthons are homotopic. The Ch
modules are supposed to undergo self-association through double
EBIs as established through the CGP-based recognition units,
whereas the Hal building blocks should interact with the Ch
counterpart through XBIs.
Scheme 1. Schematic representation of the molecular modules Ch
and Hal and of the general structure of the supramolecular
polymer at the solid state.
Depending on the role taken in the formation of the interaction
and the nature of the functional group on the Ch synthon, the
Hal module can act either as XB-donor or EB-acceptor.[25]
Supramolecular polymers at the solid state with a repetition
unit of (Ch2Hal)n are expected to form upon evaporation of a
solution containing a mixture of both Ch and Hal components. The
designed supramolecular Ch and Hal synthons are depicted in
Scheme 2. While CGP-based molecules 1E and 2E feature a XB-
acceptor pyridyl-type substituent, modules 4E and 5E expose at
2-position bromo- and iodo-tetrafluorophenyl moieties. Both Se-
and Te-congeners were synthesized following the protocols
previously reported by us (see SI for the synthesis).[16a, 27] As
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far as the ditopic Hal synthons are concerned, hexadecafluoro-
1,8-diiodooctane (HDFIO) and 1,4-diiodo-2,3,5,6-
tetrafluorobenzene (DITFB) were chosen as XB donors, and 4,4’-
bipyridyl (biPy) and 1,4-diazabicyclo[2.2.2]octane (DABCO) as XB
acceptors.[25] These modules are well-known building blocks used
to trigger XBIs at the solid state.[25]
Scheme 2. Chemical structure of the self-assembly ditopic
synthons.
At last, reference benzochalcogenazole 3Te[16e,26] was also prepared
and studied in combinations with the appropriate XB donor. It is
expected that molecule 3Te forms wire-like structures through
Te…NC interactions,[16e] and lateral XB contacts engaging the
pyridyl moiety with the ditopic XB acceptor (Hal). The
anticipated repeating units of the devised supramolecular
polymers are reported in Schemes 3 and 4.
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Scheme 3. Envisaged supramolecular polymers deriving from the
combinations of molecules 1E, 2E and 3E with either HDFIO or DITFB
XB-donor synthons.
Te-analogues 1Te and 2Te are expected to engage in frontal double
EBIs leading to dimers, which could successively express XB
contacts with either HDFIO or DITFB (Scheme 3). Likewise,
molecules 4E and 5E (Scheme 4) are expected to dimerise though
double EBIs and undergo polymerisation in the presence of biPy
and DABCO through XBIs with Br/I atoms. To validate the
recognition abilities of the designed self-assembling synthons,
we used electrostatic surface potential (ESP)[16e, 23b, 27] and
estimated the value (Vs,max) at the point of the highest charge
for both donor and acceptor atoms at B97D3/Def2-TZVP level of
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theory using Gaussian09 including D01 revision.[16e, 23b, 27] The ESPs
of all molecular modules are shown in Table 1.
Scheme 4. Envisaged supramolecular polymers deriving from the
combinations of molecules 4Te and 5Te with either biPy or DABCO
XB-acceptor synthons.
The images highlight positive potential regions (blue) around
Te, Se, Br and I atoms and electron donor as negative potential
region (red) around N atoms. The surface around the halogens and
chalcogen atoms are clearly distributed in two parts: the s-hole
(in blue) and the negative belt (yellow-green). As expected, the
s-holes are deeper for Te and I than for Se and Br atoms.
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Table 1. Calculated ESP and Vs,max values (kcal mol-1). Np = N of
pyridyl ring, Nc = N of chalcogenazole ring, X = N, Br, I
(heteroatoms engaging in XBIs).
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For the sake of this work, we will focus only on the s-hole(a)
as the s-hole(b) do not intervein in the formation of the EBIs
in these systems (the s-hole(a) and s-hole(b) for describing
positive electrostatic regions on the chalcogen atom exposed on
the side of the 4- and 2-positions, respectively, as proposed
previously by us).[16e] The formation of the supramolecular
polymers is discussed considering ESPs (Table 1). As already
suggested previously,[16e, 23b] the s-hole displaying the highest
positive Vs,max value will engage in the SBI with the functional
group featuring the most electronegative heteroatom (i.e., the
most negative Vs,max value).[16e, 23b]
Results and discussion
Co-crystal preparation. All co-crystallization attempts are
summarized in Table 2. Solutions of the given components in a
stoichiometry of choice were prepared in CHCl3 and left standing
for slow evaporation. The nomenclature of each co-crystals is
given by the minimal repetition unit of the supramolecular
structure formed at the solid state, whereas the supramolecular
species (oligomers and polymers) triggered by the chalcogen- and
halogen-bonding in the co-crystal are labelled as polymeric
structures (Table 2). Molecule 1Te forms co-crystals 2:1 with
both HDFIO and DITFB, mirroring the solution stoichiometry
(entries 1 and 2). Co-crystals with 1:1 and 1:2 stoichiometries
containing supramolecular polymer (1Te•DITFB)n and aggregate
(1Te•(DITFB)2)n could be obtained with DITFB when starting from
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solutions of 1:1 and 1:10 ratios, respectively (entries 3 and
4).
Table 2. Co-crystallization attempts, stoichiometries in
solution (o:p)sol and in the resulting co-crystals (o:p)coc (with
the o and p standing for the Ch and Hal components,
respectively). Solvent: CHCl3. *Crystal segregation.
Supramolecular
Entry Ch Hal (o:p)sol (o:p)coc Co-crystal
entity
1 1Te HDFIO 2:1
2 1Te DITFB 2:1
3 1Te DITFB 1:1
4 1Te DITFB 1:10
5 2Te HDFIO 2:1
6 2Te DITFB 2:1
7 2Te DITFB 1:1
8 2Te DITFB 1:3
9 3Te HDFIO 2:1
10 3Te DITFB 2:1
11 1Se HDFIO 2:1
12 1Se DITFB 2:1
13 1Se DITFB 1:1
14 1Se DITFB 1:10
15 2Se DITFB 2:1
2:1
2:1
1Te2•HDFIO (1Te2•HDFIO)n
1Te2•DITFB (1Te2•DITFB)2
1:1 1Te•(DITFB)n (1Te•DITFB)n
1:2 1Te•(DITFB)2 (1Te•(DITFB)2)n
-*
-
-
2:1
2:1
2:1
2:1
2:1
-*
2Te2•DITFB (2Te2•DITFB)n
2Te2•DITFB (2Te2•DITFB)n
2Te2•DITFB (2Te2•DITFB)n
3Te2•HDFIO
3Te2•DITFB
-
3Te2•HDFIO
3Te2•DITFB
-
2:1
2:1
1Se2•DITFB (1Se2•DITFB)2
1Se2•DITFB (1Se2•DITFB)2
1:2 1Se•(DITFB)2 (1Se•(DITFB)2)n
2:1
2Se2•DITFB (2Se2•DITFB)n
16 4Te biPy
2:1
-*
-
-
-
-
-
-
-
-
17 4Te DABCO 2:1/10:1 -*
18 5Te biPy 2:1/10:1 -*
19 5Te DABCO 1:2
20 5Te DABCO 1:5
21 5Te DABCO 1:10
-*
2:1
1:1
1:1
5Te2•DABCO (5Te2•DABCO)n
5Te•DABCO
1Te•5Te
(5Te•DABCO)2
(1Te•5Te)n
22 1Te
5
1:1
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Crystal segregation was observed when isomer 2Te was co-
crystallized with HDFIO (entry 5), whereas polymer (2Te2•DITFB)n
crashed out from the solution with DITFB independently on the
solution stoichiometry (entries 6–8). Notably, reference
molecule 3Te forms co-crystals with 2:1 stoichiometry with both
XB donors (entries 9 and 10, respectively). Evaporation of a
solution of Se-analogue 1Se with HDFIO did not give rise to any
co-crystals (entry 11), whereas solutions containing 2:1 and 1:1
ratio of DITFB (entries 12 and 13) exclusively gave co-crystals
with stoichiometry of 2:1, with the molecules aggregated as
supramolecular hexamers (1Se2•DITFB)2. Notably, when using an
excess of DITFB (1:10), co-crystals of aggregate (1Se•(DITFB)2)n
were formed (entry 14), as observed with the Te-analogue. Moving
to the pyrid-3-yl isomer (2Se), co-crystals of stoichiometry 2:1
were obtained as large yellow plates, also containing a polymer-
like organization (entry 15). When we reversed the XB demand,
co-crystallization experiments with compound 4Te in the presence
of biPy and DABCO were unsuccessful (entries 16 and 17,
respectively) and crystal segregation was observed. Similar
results were obtained with iodo-derivative 5Te with both biPy and
DABCO. However, when using an excess of DABCO, co-crystals with
2:1 and 1:1 stoichiometries were obtained as large yellow prisms
(entries 20 and 21, respectively). While the 2:1 solid contains
supramolecular polymer (5Te2•DABCO)n,cin the 1:1 co-crystal the
molecules are arranged as tetrameric species, (5Te•DABCO)2.
Finally, when mixing XB acceptor 1Te and XB donor 5Te in a 1:1
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ratio in CHCl3, co-crystals 1:1 containing polymer (1Te•5Te)n were
obtained (entry 22).
Solid-state supramolecular polymers with Te-CGP bearing halogen-
bond acceptors. X-ray diffraction analysis of co-crystals
1Te2•HDFIO reveals the formation of supramolecular polymer
(1Te2•HDFIO)n through a 2:1 association (Fig. 1).
Figure 1. X-ray structure of co-crystal 1Te2•HDFIO a) evidencing
the formation of polymer (1Te2•HDFIO)n; b) vdW sphere
representation of the layered organization; c) p-p stacking
ꢁ
arrangement. Space group: Pꢀ. Atom colors: blue N, ocher Te,
yellow F, pink I, gray C.
One can easily discern the dimeric association of the CGP motif
through double EBIs (dN...Te = 2.998 Å). Each pair of 1Te sandwiches
a molecule of HDFIO through two XB contacts established with the
pyrid-4-yl moieties (dN...I
= 2.732 Å). Notably,
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tellurazolopyridine 1Te arranges in columnar p-p stacks (estimated
dp-p = 3.465 Å) in a head-to-tail arrangement (Fig. 1c) separated
by a layer of HDFIO. The solid-state arrangement led to a
segregation between the fluorinated (pink arrows) and non-
fluorinated (grey arrows) moieties (Fig. 1b). Replacing HDFIO
with DITFB (Fig. 2) led to polymer (1Te2•DITFB)n.
Figure 2. X-ray structure of co-crystal 1Te2•DITFB, forming a)
hexameric units (1Te2•DITFB)2; b) vdW sphere representation of the
ꢁ
layered organization; c) off-set arrangement. Space group: Pꢀ.
Atom colors: blue N, ocher Te, yellow F, pink I, gray C.
In this case, the synthons arrange in hexameric structures
(contoured with a red dashed line), where the two central CGP
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moieties liaise through double EBIs (dN...Te = 3.164 Å) and DITFB
is sandwiched between two pyrid-4-yl moieties (dN...I = 2.793 Å).
Each hexamer is brought together by weak HB interactions engaging
the H-atom in 6-position of the terminal CGP group and two F
atoms from DITFB (dF...H-C = 3.078 Å). Those interactions organize
the hexamer in a quasi-planar arrangement (off-set between two
overlapping layers: 0.912 Å, Fig. 2c). In addition, DITFB
interacts with two CGP units through quasi-parallel p-p stacking
interactions (Fig. 2c). Molecule 1Te arranges in a head-to-tail
fashion (estimated dp-p = 3.490 Å) and the fluorinated aromatic
is sandwiched between two tellurazolopyridines (dp-p = 3.580 Å).
Figure 3. X-ray structure of co-crystal 1Te•DITFB evidencing only
the formation of XBIs. Space group: P21/n. Atom colors: blue N,
ocher Te, yellow F, pink I, gray C.
Looking at the ESP map (Fig. S18), one can observe that the
p-surfaces of DITFB and CGP feature opposite potentials. This
complementary quadrupolar charge distribution is likely to
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govern the face-to-face arrangement at the solid state. In
analogy to the 1:1 case (1Te•DITFB, Fig. 3), the 1:2 co-crystals
(1Te•(DITFB)2, Fig. 4) does not show any noticeable double EBIs
between the CGP moieties. Rather, only XBIs and HBIs are present
(Fig. 4). Specifically, DITFB interacts through XB contacts with
the pyrid-4-yl (dN...I 2.804 Å) and the CGP (dN...I = 2.754) groups.
Figure 4. X-ray structure of 1Te•(DITFB)2 evidencing only the
ꢁ
formation of XBIs. Space group: Pꢀ. Atom colors: blue N, ocher
Te, green F, pink I, gray C.
When compared to the solid-state arrangement of 1Te•DITFB (Fig.
3), the XBI established with the CGP moiety is shorter than that
formed with the pyrid-4-yl moieties. As observed in the co-
crystals of 1Te•DITFB, the I and Te atoms interact through weak
EBIs (dI...Te = 4.005 Å, SvdW = 4.04 Å), with the former atom acting
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as the chalcogen-bond donor and the latter as the chalcogen-bond
acceptor (Fig. 3).
When moving to the co-crystals of molecules 2Te and DITFB,
supramolecular polymer (2Te2•DITFB)n was formed independently on
the stoichiometry (Table 2, Fig. 5). The structure displays the
CGP group engaging into double EBIs (dN...Te = 3.068 Å), and the
two pyrid-3-yl moieties forming XBIs (dN...I = 2.738 Å) with DITFB.
Both 2Te and DITFB homomolecularly p-p stack (dp-p = 3.544 Å and
3.459 Å, off-set of 2.945 Å and 3.339 Å, Fig. S20).
Te
ꢁ
Figure 5. X-ray structure of 2 2•DITFB. Space group: Pꢀ. Atom
colors: blue N, ocher Te, yellow F, pink I, gray C.
In this arrangement, the pyrid-4-yl group interacts with a CGP
moiety through a double hetero non-covalent interaction, namely
frontal EBI (dN...Te = 3.000 Å) and HBI (dN...C = 3.568 Å). The CGP
group of the inverted arrangement interacts through an XBI with
DITFB (dN...I = 2.984 Å). At the molecular level, one can easily
notice that the ESP is rather symmetrical (Fig. 6b), suggesting
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that both electrostatic arrangements are possible without
significantly disrupting the crystal organisation (Fig. 6c).
Figure 6. The two arrangement modes a) and c) for molecule 2Te
in 2Te2•DITFB. b) ESP map for 2Te, level of theory: B97D3/Def2-
TZVP using Gaussian09 including D01 revision. Atom colors: blue
N, ocher Te, yellow F, pink I, gray C.
Moving to reference molecule 3Te, co-crystals with 2:1
stoichiometry, 3Te2•HDFIO (Fig. 7) and 3Te2•DITFB (Fig. 8), were
obtained with both molecules HDFIO and DITFB, respectively. As
far as 3Te2•HDFIO is concerned, no EBIs have been observed. Only
XBIs between pyrid-4-yl moieties and HDFIO were present (dN...I =
2.772 Å and 2.819 Å, Fig. 7). As in the case of 1Te2•HDFIO, a
segregation of the fluorinated (indicated by pink arrows) and
non-fluorinated (indicated by grey arrows) synthons is observed.
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Figure 7. X-ray structure of co-crystal 3Te2•HDFIO displaying the
a) structure of repetitive unit 3Te2•HDFIO; b) vdW sphere
representation of the layered organization; c) p-p stacking
ꢁ
arrangement. Space group: Pꢀ. Atom colors: blue N, ocher Te,
yellow F, pink I, gray C.
The X-ray diffraction analysis of co-crystal 3Te2•DITFB (Fig. 8)
shows the presence of trimeric units in which the XB donor is
sandwiched between two pyrid-4-yl moieties through XBIs (dN...I =
2.823 Å). Moreover, the tellurazole unit engages in an EBI with
one of the F atoms of DITFB (dF...Te = 3.294 Å). Similarly to
1Te2•DITFB, quasi-parallel p-p stacks are formed, alternating one
DITFB module and two molecules of 3Te (estimated dp-p = 3.370 Å
between DITFB and 3Te, dp-p = 3.690 Å between two 3Te), the latter
being arranged in a head-to-tail fashion (Fig. 8b-c). Taken all
together, the studies with reference molecule 3Te suggested that
synthons forming only single EBIs are not ideal candidates for
engineering co-crystals with concurring XBIs.
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Figure 8. a) X-ray structure of 2:1 co-crystal 3Te2•DITFB; b) vdW
sphere representation; c) p-p stacking arrangement. Space group:
ꢁ
Pꢀ. Atom colors: blue N, ocher Te, yellow F, pink I, gray C.
Solid-state supramolecular polymers with Se-CGP bearing halogen-
bond acceptors. To study the effect of the chalcogen atom donor,
we also have grown co-crystals between the Se-doped CGP
derivatives (1Se and 2Se) and the halogen-donor modules (Table 2).
X-ray analysis of 1Se2•DITFB (Fig. 9) reveals that the molecules
associate in hexameric structures (1Se2•DITFB)2, as observed for
1Te2•DITFB (Fig. 1). In the hexamer, the two central CGP groups
interact through frontal dual EBIs (dN...Se = 3.294 Å) while
establishing lateral XB contacts with DITFB (dN...I = 2.779 Å). In
the crystal packing, the hexamers are connected through weak
HBIs between the hydrogen atom in the 6-position of terminal CGP
moieties and the F atoms (dF...C = 3.088 Å). This forces all
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modules to adopt a quasi-planar arrangement, displaying a minor
misalignment of 0.976 Å (Fig. 9c). These observations contrast
previous results in the group, for which the X-ray structure of
crystals containing only 1Se did not show any EBIs dimerization.
Figure 9. X-ray structure of co-crystal 1Se2•DITFB. a)
Supramolecular polymer; b) vdW sphere representation; c) capped
ꢁ
stick representation of the miss-alignment. Space group: Pꢀ.
Atom colors: blue N, ocher Te, yellow F, pink I, gray C.
However, when looking at ESP map of 1Se•DITFB (Fig. 10), one can
notice Vs,max value of the Se-centered s(a) has increased to +11.3
kcal mol-1 upon interaction with DITFB from the value of +7.09
kcal mol-1 for molecule 1Se alone. This suggests that once a pyrid-
4-yl moiety contacts a DITFB, it seemingly depletes the Se-CGP
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moiety, raising the strength of the double EBIs. This observation
is accordance with previous results, for which CF3-bearing Se-
CGP derivatives form doubly EB-bonded dimers.[26b]
Figure 10. ESP map of 1Se (left) and of a 1Se•DITFB complex held
by a XBI (right). Extreme values of interest are highlighted.
Level of theory: B97D3/Def2-TZVP using Gaussian09 including D01
revision.
Figure 11. X-ray structure of 1:2 co-crystal 1Se•(DITFB)2
ꢁ
evidencing the key SBIs. Space group: Pꢀ. Atom colors: blue N,
ocher Te, yellow F, pink I, gray C.
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10.1002/chem.201904762
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Co-crystal 1Se•(DITFB)2 is iso-structural to 1Te•(DITFB)2. The
pyrid-4-yl groups and the CGP moieties interact with two
crystallographically independent molecules of DITFB through XB
contacts (dN...I 2.804 Å and dN...I = 2.798 Å, respectively, Fig.
11). In contrast to the case of 1Te•(DITFB)2, no XBs are observed
between Se and I atoms. Crystallization experiments using isomer
2Se led to co-crystal 2Se2•DITFB (Fig. 12).
Figure 12. X-ray structure of co-crystal 2Se2•DITFB. a)
Supramolecular polymer; b) vdW sphere representation of the
layered organization; c) capped stick representation of the p-p
ꢁ
stacking. Space group: Pꢀ. Atom colors: blue N, ocher Te, yellow
F, pink I, gray C.
In the structure, the Se-derivative associate in dimers through
HB interactions (dN...C = 3.560 Å) and develop into a
supramolecular polymer through XB contacts with the I atom (dN...I
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10.1002/chem.201904762
Chemistry - A European Journal
= 2.858 Å). This results in a quasi-co-planar organization of
the molecules. In addition, 2Se and DITFB interact through p-p
stacking (p-p = 3.548 Å and 3.409 Å, with an off-set of 1.843 Å
and 2.089 Å, respectively) piling into columns of fluorinated
(indicated by pink arrows) and non-fluorinated (indicated by
grey arrows) domains (Fig. 12b-c). Surprisingly, the co-crystals
do not feature any EBIs, in contrast to the case of 1Se2•DITFB.
Figure 13. ESP map of molecule 2Se alone (left) and with DITFB
through XBI (right). Level of theory: B97D3/Def2-TZVP using
Gaussian09 including D01 revision.
The ESP maps of 2Se and 1Se (Fig. 13) show that the pyrid-3-yl
isomer displays s-hole(a) with a smaller Vs,max value than that of
the pyrid-4-yl congener (+5.02 kcal mol-1 and +7.09 kcal mol-1,
respectively). Upon interaction with DITFB, an increase of 4
kcal mol-1 is observed for the s-hole(a) (+9.41 kcal mol-1 and
+11.3 kcal mol-1, respectively), which is too weak to trigger any
EBIs.
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10.1002/chem.201904762
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Solid-state supramolecular polymers with Te-CGP bearing halogen-
bond donors. Moving to the CGP derivative substituted with 4-
iodo-tetrafluorophenyl, co-crystal 5Te2•DABCO was obtained as two
ꢁ
polymorphs with space groups Pꢀ (A) and P21/n (B) under the same
crystallisation conditions.
Figure 14. X-ray structure of co-crystal 5Te2•DABCO as polymorph
A. a) Supramolecular polymer and key SBIs; b) vdW sphere
representation of the layered organization; c-d) p-p stacking
ꢁ
and CH-p interaction. Space group: Pꢀ. Atom colors: blue N, ocher
Te, yellow F, pink I, gray C.
In polymorph A (Fig. 14), 5Te dimerizes through double EBIs (dN...Te
= 2.923 Å), with the complexes bridged into a supramolecular
polymer through XB bonds (dN...I = 2.722 Å) with DABCO linkers.
Molecules 5Te p-p stack in a quasi-parallel head-to-tail fashion
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10.1002/chem.201904762
Chemistry - A European Journal
(estimated dp-p = 3.710 Å, Fig. 14b-c). DABCO molecules are
sandwiched between two CGP moieties through CH-p interactions
(dC...N = 3.229-3.684 Å, Fig. 15d).
Figure 15. X-ray structure of co-crystal 5Te2•DABCO as polymorph
B. a) Supramolecular polymer and key SBIs; c) p-p stacking and
CH-p interactions; c) disorted 5Te. Space group: P21/n. Atom
colors: blue N, ocher Te, yellow F, pink I, gray C.
Polymorph B of 5Te2•DABCO was also obtained (Fig. 15), in which
molecule 5Te interacts through double EBIs (dN...Te = 2.974 Å) to
form (5Te)2 units, and a DABCO linker is sandwiched between dimers
through XBIs (dN...I = 2.694 Å). Notably, one Te-CGP molecule in
the asymmetric unit is distorted, with a deviation from the
planarity of 23°. While polymorph A was obtained only once,
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10.1002/chem.201904762
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polymorph B could be reproducibly obtained under the
crystallisation conditions described above.
Figure 16. X-ray structure of co-crystal 5Te•DABCO. a)
Supramolecular polymer and key SBIs; b) vdW sphere
representation of the layered organization; c) p-p stacking
ꢁ
interactions. Space group: Pꢀ. Atom colors: blue N, ocher Te,
green F, pink I, gray C.
On the other hands, when growing co-crystals from mixtures
containing a 1:10 ratio of 5Te and DABCO, co-crystal 5Te•DABCO
could be obtained. The two components arrange into tetrameric
units (Fig. 16, contoured with a red dashed line) where the two
central CGP moieties interact through double EBIs (dN...Te = 2.926
Å) and the DABCO through XBIs (dN...I = 2.703 Å). As observed for
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10.1002/chem.201904762
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5Te2•DABCO, also in this case the molecules undergo p-p stacking
organization (p-p = 3.289 Å), segregating the synthons into
fluorinated (indicated by pink arrows) and non-fluorinated
(indicated by grey arrows) domains (Fig. 16b).
At last, when mixing molecules 1Te and 5Te, supramolecular polymer
1Te•5Te was obtained (Fig. 17). Notably, heteromolecular dimers
are formed between molecules 1Te and 5Te through distorted double
EBIs (dN...Te = 3.033 Å, the two CGP moieties sit on planes forming
an angle of 33°). In turn, the dimers interact through XBIs (dN...I
= 2.802 Å) in a linear fashion (C-I…N angle = 172°), forming a
polymeric structure. Interestingly, the supramolecular polymer
(1Te•5Te)2 arranges in a triple-helix structure (Fig. 17b).
Figure 19. X-ray structure of co-crystal 1Te•5. a) Supramolecular
polymer and key SBIs; b) capped stick representation of the
triple helix. Space group: P21/n. Atom colors: blue N, ocher Te,
green F, pink I, gray C.
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In addition, molecules of 1Te and 5Te interact through quasi-
parallel π-π stacking in an antiparallel fashion (Fig. S23).
Both the electron deficient 4-iodotetrafluorophenyl and pyrid-
4-yl groups interact with the CGP moiety (ESP maps are provided
to indicate the charge distribution).
Conclusions.
In summary, we have demonstrated the possibility to form
supramolecular polymers at the solid-state exploiting the
simultaneous expression of both XBIs and EBIs. Capitalizing on
a preliminary study previusly reported by us using the chalcogen-
bonding CGP recognition motif,[23b] in this work we have programmed
molecular modules with either a halogen bond acceptor or donor
that, interacting with suitable complementary building blocks,
undergo the formation of wire-like assemblies at the solid state.
In the majority of the solids, both XBIs and EBIs take place
without interfering with each other. In particular, mixing 1Te
and DITFB, different crystals ((1Te)2•DITFB, 1Te•DITFB,
1Te•(DITFB)2) could be obtained depending on the solution ratio
of the two components. Isomer 2Te led to the formation of only
(2Te)2•DITFB, independently on the initial ratio of the two
components. Interestingly, when reference benzotellurazole 3 is
used, only halogen-bonding interactions were observed, thus
supporting our engineering principle for which the persistency
of the CGP recognition motif is crucial to achieve the
simultaneous expression of both SBIs. When passing to the Se-
29
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