Organic selenocyanates as strong and directional chalcogen bond donors for crystal engineering

Article abstract of DOI:10.1039/c7cc04833e

Organic bis(selenocyanate) derivatives act as powerful chalcogen bond donors for the elaboration of 1D extended structures upon co-crystallization with 4,4′-bipyridine as a ditopic chalcogen bond acceptor.

Full text of DOI:10.1039/c7cc04833e

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Organic selenocyanates as strong and directional
chalcogen bond donors for crystal engineering†
Cite this:DOI: 10.1039/c7cc04833e
Huu-Tri Huynh, Olivier Jeannin and Marc Fourmigue
*
´
Received 21st June 2017,
Accepted 7th July 2017
DOI: 10.1039/c7cc04833e
rsc.li/chemcomm
Organic bis(selenocyanate) derivatives act as powerful chalcogen chalcogen bonding.14 There are however no examples of the
bond donors for the elaboration of 1D extended structures formation of chalcogen-bonded co-crystals associating for example
upon co-crystallization with 4,40-bipyridine as a ditopic chalcogen a ditopic chalcogen bond donor with a ditopic Lewis base as a
bond acceptor.
chalcogen bond acceptor, in a vein similar to the very success-
ful examples introduced in halogen-bonded systems with
The renaissance of halogen bonding1 in the last 20 years is largely a,o-diiodoperfluoroalkanes15 or para-diiodotetrafluorobenzene.4
rooted in the development of crystal engineering strategies2 for the
In that respect, we considered organic selenocyanates
controlled formation of extended polymeric 1D, 2D or 3D struc- R–Se–CN as potentially efficient chalcogen bond donors. It is
tures through co-crystal formation.3 For example, the association expected indeed that the electron-withdrawing nature of the
of para-diiodotetrafluorobenzene as a ditopic halogen bond donor nitrile group will favour the formation of one single strong
with a large variety of Lewis bases4 has led today to more than 220 s-hole on the selenium atom, in the prolongation of the NC–Se
structurally characterized co-crystals.5 The efficiency of halogen bond. A CSD investigation of reported structures of organic seleno-
bonding finds here its origin in its predictability, a direct conse- cyanates confirmed our initial assumption.16 Indeed, most of the
quence of its directionality due to the highly localized s-hole simple aliphatic and aromatic organic selenocyanates do crystal-
which develops on the halogen atom.6 This concept of s-hole is lise with chalcogen bond interactions. In the absence of other
not restricted to halogens but is also found in the heaviest Lewis bases, the selenium atom actually interacts with the nitro-
elements of groups 14–16.7 In the chalcogen series, calculations gen atom of a neighbouring selenocyanate moiety, giving rise to
performed on molecules like S(CN)2, Se(CN)2,8 and Cl3C–S–CN,9 recurrent chain-like motifs, as in benzylselenocyanate (Fig. 1a),17
show indeed the presence of two sizeable s-hole sites on the and ortho-bis(selenocyanatomethyl)benzene,18 (Fig. 1b) or para-
chalcogen atoms, in the prolongation of the two C–S(Se) bonds, bis(selenocyanatomethyl)benzene.19
also confirmed by an experimental charge density determination
Note the Seꢀ ꢀ ꢀN distances are in the range of 2.97–3.11 Å, i.e.
on selenophtalic anhydride.10 Nevertheless, the specific use of notably shorter than 3.45 Å, the sum of the van der Waals radii
chalcogen bond donors in crystal engineering for the elaboration
of extended 1D, 2D or 3D solid state structures is up to now very
limited, probably because the presence of the two s-holes limits
the required predictability of the interaction. One can mention
however self-assembly through chalcogen bonding in molecules
like benzo-2,1,3-selenadiazoles,11 benzo-1,3-tellurazoles,12 or
iso-tellurazole N-oxides,13 bearing simultaneously an activated
chalcogen atom and a Lewis base. Also, the close proximity of
two chalcogen atoms in activated bithiophene or biseleno-
phene derivatives can be used to chelate small anions through
´
Institut des Sciences Chimiques de Rennes (ISCR), UMR 6226 Universite de Rennes
1 and CNRS, Campus de Beaulieu, 35042 Rennes, France.
E-mail: marc.fourmigue@univ-rennes1.fr
† CCDC 1557620–1557622, Cif files for the X-ray crystal structures of 2, (2ꢀbipy)
and (3ꢀbipy). For crystallographic data in CIF or other electronic format see DOI:
10.1039/c7cc04833e
Fig. 1 Detail of the reported solid state structures of (a) benzylselenocyanate
and (b) ortho-bis(selenocyanatomethyl)benzene. H atoms have been omitted
and the orange dotted lines indicate the chalcogen bond interaction.
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Table 1 Chalcogen bond characteristics of the crystalline 1–3 derivatives
of Se (1.90 Å) and nitrogen (1.55 Å). The recurrence of this
robust Seꢀ ꢀ ꢀN chalcogen-bonded motif lets us infer that specifi-
cally the three ditopic ortho-, meta- and para-bis(selenocyanato-
methyl)benzenes, noted 1–3 in the following, could be
themselves very good candidates to prepare, by analogy with diiodo
derivatives mentioned above, co-crystals exhibiting similar
predictable 1D supramolecular motifs. We therefore investigated
the co-crystallisation of these three ditopic chalcogen bond
donors 1–3 with, as a first example of a ditopic Lewis base,
4,40-bipyridine, as detailed below.
The preparation of the three chalcogen bond donors 1–3
is based on the reaction of potassium selenocyanate with the
ortho-, meta- and para-bis(bromomethyl)benzene in acetone,
as described earlier.19,20 The solid state structure of the meta
isomer 2 was unknown, at variance with those of the ortho and
para isomers 1 and 3.18,19 Compound 2 crystallises in the mono-
clinic system, space group Cc, with two crystallographically
independent molecules in the unit cell (Fig. 2).‡
Seꢀ ꢀ ꢀN (Å)
C–Seꢀ ꢀ ꢀN (1)
Seꢀ ꢀ ꢀNRC (1)
Ref.
2
Se1
Se2
Se3
Se4
3.010(24)
3.015(24)
2.965(24)
3.017(24)
172.9(7)
174.1(7)
175.9(7)
175.7(7)
172(2)
173(2)
174(2)
176(2)
This work
3
Se1
Se2
3.022(18)
2.997(18)
171.8(5)
174.4(8)
166(1)
177(2)
19
18
1
Se1
Se2
2.969(9)
2.985(8)
172.6(3)
172.9(3)
174.0(7)
173.2(7)
both partners in equimolar quantities. Despite our efforts, good
quality crystals were obtained only from 2 and 3, affording 1 : 1
adducts. (2ꢀbipy) crystallises in the monoclinic system, space
group C2/c, with the meta derivative 2 located on a two-fold axis,
and the 4,40-bipyridine on an inversion centre, hence the 1 : 1
stoichiometry. As shown in Fig. 3, the nitrogen atom of the
pyridine moiety competes now efficiently with the nitrogen atom of
the nitrile to engage in a short and directional chalcogen bond,
whose structural characteristics are collected in Table 2. This gives
rise to the formation of hetero-molecular chains running along the
(4a–c) direction. Note the particularly strong chalcogen bonding
interaction, with a reduction ratio21 down to 0.82 and a strong
linearity, while the orientation of the lone pair of the pyridine
moiety is not fully optimal since the angle between the Nbipy–Cg
molecular axis and the SeꢀꢀꢀN direction amounts to only 1651.
The efficiency of this chalcogen-bonding motif is also evidenced
from the crystal structure obtained with the para isomer, namely
The molecules are again associated through short Seꢀ ꢀ ꢀN
chalcogen bonds forming chains running along the a direction.
Structural characteristics of these chalcogen bonds (Table 1) were
compared with those reported earlier for the ortho and para
derivatives (Fig. 1b and c), showing the same strong linearity, with
a notable reduction ratio,21 between 0.86 and 0.88. Note also that
the robustness of this supramolecular SeꢀꢀꢀN motif most probably
finds a further origin in the cooperativity it can develop along the
chains. Indeed, the formation of the chalcogen bond on the
nitrogen side leads to a decreased charge density on this atom,
and by extension on the covalently linked selenium atom, whose
electrophilic character is then enhanced. Such cooperativity effects
have been demonstrated from theoretical calculations22,23 on
dimer, trimer and infinite one-dimensional chain models formed
by Se(CN)2 or Te(CN)2, as these compounds adopt indeed this 1D
motif in their experimental solid state structures.24,25
%
(3ꢀbipy). It crystallises in the triclinic system, space group P1, with
both meta-bis(selenocyanatomethyl)benzene 3 and 4,40-bipyridine
located on inversion centres, hence the 1 : 1 stoichiometry. As shown
in Fig. 4, chalcogen bonding interactions between the ditopic donors
and acceptors again favour the formation of chains, running
here along the (2a–c) direction, with structural characteristics
(Table 2) comparable to those found in (2ꢀbipy).
The formation of co-crystals between 1–3 and 4,40-bipyridine
was performed via diffusion of Et2O over an acetone solution of
In conclusion, we have highlighted here the very strong
tendency of organic selenocyanates to self-crystallise through
efficient SeꢀꢀꢀNRC chalcogen bonding interactions. Competitive
crystallizations of bis-selenocyanates with a stronger ditopic Lewis
base (4,40-bipyridine) leads to recurrent 1D structures with direc-
tional and even shorter SeꢀꢀꢀNbipy chalcogen bonds. These examples
Fig. 2 Solid state organization of 2, showing the chains formed out of the
two crystallographically independent molecules. Symmetry operations:
(i) 1 + x, y, z; (ii) ꢁ1 + x, y, z. The orange dotted lines indicate the chalcogen
bond interaction.
Fig. 3 Detail of one chalcogen-bonded chain running along the (4 + x,
y, ꢁ1 + z) direction in (2ꢀbipy). The orange dotted lines indicate the
chalcogen bond interaction.
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Table 2 Chalcogen bond characteristics of the (2ꢀbipy) and (3ꢀbipy)
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Seꢀ ꢀ ꢀN (Å)
2.830(3)
2.897(4)
C–Seꢀ ꢀ ꢀN (1)
177.2(1)
176.7(1)
Seꢀ ꢀ ꢀN–Cg (1)
165.0(1)
165.9(1)
(2ꢀbipy)
(3ꢀbipy)
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Fig. 4 Detail of one chalcogen-bonded chain running along the (2a–c)
direction in (3ꢀbipy). The orange dotted lines indicate the chalcogen bond
interaction.
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demonstrate that organic selenocyanates are efficient building
blocks in crystal engineering strategies. By analogy with halogen
bonding, they can probably be used also for other applications, such
as liquid crystals and gels, anion recognition or organocatalysis.
Notes and references
‡ Crystal data for 2: C10H8N2Se2, M = 314.10 g molꢁ1, crystal dimensions
0.21 ꢂ 0.02 ꢂ 0.01 mm, monoclinic, space group Cc, a = 5.9696(7) Å,
b = 36.720(4) Å, c = 10.2124(11) Å, b = 95.401(6)1, V = 2228.7(4) Å3, Z = 8,
r
calcd = 1.872 g cmꢁ3, F(000) = 1200, m = 6.597 mmꢁ1, T = 293 K, 2ymax
=
16 With intramolecular chalcogen bonds, see CCDC: AHEQIN, FAGGAV,
GIYJUV. For aromatic selenocyanates: BATDIJ, CIBFUP, KABTAJ,
KABTEN, WERYAT, SECNBZ. For aliphatic selenocyanates: GOHMEW,
ZUTTAL, CIGGEE, SOHQOX, YUNSIK.
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55.371. Final results (for 253 parameters) were R1 = 0.0529, wR2 = 0.10 and
S = 1.018 for 3849 independent reflections [2328 with I 4 2s(I)]. Crystal
data for (2ꢀbipy): C20H16N4Se2, M = 470.29 g molꢁ1, crystal dimensions
0.13 ꢂ 0.08 ꢂ 0.04 mm, monoclinic, space group C2/c, a = 5.1880(5) Å,
b = 14.9962(13) Å, c = 25.101(2) Å, b = 92.613(3)1, V = 1950.8(3) Å3, Z = 4,
rcalcd = 1.601 g cmꢁ3, F(000) = 928, m = 3.801 mmꢁ1, T = 293 K, 2ymax
=
61.1581. Final results (for 119 parameters) were R1 = 0.037, wR2 = 0.0877 and
S = 1.03 for 3010 independent reflections [2147 with I 4 2s(I)]. Crystal data
for (3ꢀbipy): C20H16N4Se2, M = 470.29 g molꢁ1, crystal dimensions 0.36 ꢂ
%
0.34 ꢂ 0.06 mm, triclinic, space group P1, a = 5.3962(4) Å, b = 7.7356(6) Å,
c = 11.7477(9) Å, a = 99.421(3), b = 94.558(2), g = 104.661(2)1, V = 464.25(6) Å3,
Z = 1, rcalcd = 1.682 g cmꢁ3, F(000) = 232, m = 3.993 mmꢁ1, T = 293 K,
2ymax = 61.1021. Final results (for 118 parameters) were R1 = 0.0412,
wR2 = 0.0841 and S = 1.022 for 2831 reflections [2161 with I 4 2s(I)].
21 The reduction ratio is defined as d(XY)exp/[rvdW(X) + rvdW(Y)], where
d(XY)exp is the Xꢀ ꢀ ꢀY distance deduced from structure resolution and
rvdW(X) is the van des Waals radius of element X, defined in:
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