Crystallization of 3-cyanophenyl 4-cyanobenzoate with AgSbF6: A polar coordination network based on the crisscrossing of intertwined helices

Article abstract of DOI:10.1039/a707574j

Crystallization of 3-cyanophenyl 4-cyanobenzoate 1 with AgSbF₆ yields the non-centrosymmetric, fourfold interpenetrated grid structure [Ag(1)₂]SbF₆ 2 through the criss-crossing of two-dimensional sheets.

Full text of DOI:10.1039/a707574j

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Crystallization of 3-cyanophenyl 4-cyanobenzoate with AgSbF6: a polar
coordination network based on the crisscrossing of intertwined helices
Keith A. Hirsch, Scott R. Wilson and Jeffrey S. Moore*
Departments of Chemistry and Materials Science and Engineering, The University of Illinois at Urbana-Champaign, Roger Adams
Laboratory, Box 55-5, 600 S. Mathews Avenue, Urbana, IL 61801, USA
Crystallization of 3-cyanophenyl 4-cyanobenzoate 1 with
AgSbF6 yields the non-centrosymmetric, fourfold interpene-
trated grid structure [Ag(1)2]SbF6 2 through the criss-
crossing of two-dimensional sheets.
by a single sheet. This interpenetration may be viewed as the
intertwining of two 2/1 helices (Fig. 1). Closest-packing in
complex 2 is not achieved by twofold interpenetration. Rather,
it results from further interpenetration of twofold inter-
penetrated sheets that propagate orthogonal to one another.
Crisscrossing of orthogonal twofold sheets yields a fourfold
interpenetrated grid structure overall (see Fig. 2). p–p Stacking
is observed between molecules of ligand 1 that originate from
orthogonal sheets [Fig. 2(b)]. Specifically, stacking occurs
between cyanobenzoyl rings at a plane-to-plane distance of 3.35
Å and between cyanophenyl rings at a plane-to-plane distance
of 3.44 Å.
Fourfold interpenetration in complex 2 can be viewed as
arising from the crisscrossing of orthogonal pairs of 2/1 helices
(see Fig. 3). Orthogonal sheets are mirror images of one another
and, therefore, orthogonal helices are of opposite handedness
[Fig. 3(b)]. The reason that this structure is polar is that helices
of opposite handedness propagate orthogonal to one another.
Therefore, the opposite twist sense associated with these helices
does not cancel. Had helices of opposite handedness propagated
The construction of self-assembled materials through metal
coordination is an area of research that has grown tremendously
in recent years.1 The challenge that faces chemists working in
this field is to identify packing trends that may allow for the
rational design of functional materials. In this vein, we
developed a packing model for interpenetrated diamondoid
networks that was applied with success to our structures and
those in the literature.2 Also, many interesting structural studies
on other coordination networks have been put forth,3 and some
have yielded materials exhibiting novel properties.4 In order to
observe packing trends such that coordination network topology
may be better anticipated, systematic structural studies should
continue to elucidate the role of variables such as counterion
and ligand structure. In time, such studies may allow for the
rational construction of materials exhibiting catalytic or non-
linear optical activity. In continuing towards this goal, we report
a novel, non-centrosymmetric coordination network based on
3-cyanophenyl 4-cyanobenzoate 1. Included here is a descrip-
tion of this structure that accounts for its packing in a polar
space group.
O
O
CN
NC
1
3-Cyanophenyl 4-cyanobenzoate 1 was prepared in 92%
yield by reaction of 3-cyanophenol (1.0 equiv.) and 4-cyano-
benzoyl chloride (1.0 equiv.) in CH2Cl2 at room temperature in
the presence of DMAP (0.1 equiv.) and NEt3 (2.4 equiv.).
Crystallization of ligand 1 (1.0 equiv.) with AgSbF6 (1.1 equiv.)
was achieved by heating and slow cooling from toluene in a
programmable oven. The temperature program involved heat-
ing from room temperature to 100 °C at a rate of 20 °C h21
,
holding at 100 °C for 2 h, and cooling to ambient temperature at
a rate of 1.2 °C h21. Colorless columnar crystals of the complex
[Ag(1)2]SbF6 2 were obtained and one was selected for X-ray
analysis.† The resulting structure crystallizes in the non-
centrosymmetric, orthorhombic space group Ccc2 and is
composed of crisscrossing sheets that form an infinite grid.
In complex 2, silver(i) adopts a distorted tetrahedral geome-
try coordinated by four nitrile nitrogen atoms of ligand 1. The
metal ion bonds to nitrile nitrogens of two cyanobenzoyl rings
and two cyanophenyl rings. N–Ag–N bond angles about
2
silver(i) range from 100.4(3) to 130.1(4)°. The SbF6 ions do
not coordinate to silver(i) and are disordered over two sites,
each of which is half-occupied. The shortest Ag···F separation is
5.30 Å.
The sheet topology of complex 2 is shown in Fig. 1. Within
a sheet, the Ag–1–Ag distance is 16.11 Å. Twofold
interpenetration is observed to partially fill void space created
Fig. 1 Twofold interpenetrated sheets as a means to partially fill void space
in the grid structure [Ag(1)2]SbF6 2. Interpenetration may be viewed as the
intertwining of two 2/1 helices that are derived from the sheets as shown.
The projection at the bottom is obtained by rotation of the middle figure by
ca. 90° about the horizontal axis. The inclusion of counterions is shown in
this projection (antimony is green and fluorine is red).
Chem. Commun., 1998
13

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structures [Ag(3,3A-dicyanodiphenylacetylene)2]XF6 (X = P,
As, Sb), which we reported recently.3a These structures
crystallized in space group P1 and the topology is twofold
(b)
(a)
¯
interpenetrated sheets that are very similar to those shown in
Fig. 1. However, for the 3,3A-dicyanodiphenylacetylene struc-
tures, closest-packing arises from the interdigitation of helices
of opposite handedness3a rather than the crisscrossing of such
helices. As a result, left- and right-handed helices propagate
along the same axis such that the opposite twist sense associated
with these helices cancel out, and the structures are non-polar
¯
(P1). The difference in the packing between the structure
presented here and those of 3,3A-dicyanodiphenylacetylene may
be a result of the para-nitrile group of ligand 1, which changes
the conformation of the 2/1 helix. This comparison demon-
strates the value of viewing solid-state packing in terms of
helices in order to better understand gross structure. An
increased understanding of solid-state packing is essential if
self-assembled materials possessing novel properties are to be
designed.
We acknowledge the US Department of Energy through the
Materials Research Laboratory at the University of Illinois
(Grant DEFG02-96ER45439) for financial support of this work.
We also thank the School of Chemical Sciences Materials
Characterization Laboratory at the University of Illinois for
X-ray data collection.
Fig. 2 (a) Fourfold interpenetration in [Ag(1)2]SbF6 2 resulting from the
crisscrossing of an orthogonal pair of twofold interpenetrated sheets. The
blue and yellow networks constitute one set of twofold sheets and the red
and green networks constitute the other. The arrows indicate the directions
of propagation for the orthogonal sheets. Fourfold interpenetration is shown
from left to right in a blue–green–yellow–red sequence where the
orthogonal sheets cross. (b) Two views of p–p stacking of cyanobenzoyl
rings of compound 1 as a result of fourfold interpenetration. Stacking occurs
between ligands of orthogonal sheets along the polar c-axis. The direction
of the c-axis is indicated for the bottom projection. The plane-to-plane
distance for this stacking interaction is 3.35 Å.
Footnotes and References
* E-mail: moore@aries.scs.uiuc.edu
† Crystal data for 2: orthorhombic, space group Ccc2 (no. 37),
a = 18.9697(5), b = 21.25190(10), c = 7.5365(2) Å, U = 3038.21(11)
Å3, Dc = 1.837 g cm23, Z = 4, M = 840.09, Mo-Ka, Lp corrected, 9596
reflections collected at 275 °C, 3589 unique reflections. The structure was
solved using SHELXS and was refined using SHELXTL. 3586 Reflections
(b)
(a)
2
refined based on Fo by full-matrix least squares; number of
parameters = 237; R1 = SıFoı 2 ıFcı)/SıFoı = 0.0570 (for Fo > 4s)
1
2
2
2
2
2
and 0.1086 (for all data); wR2 = [S(wıFo 2 Fc ı)/SwıFo ı ] = 0.0804
(for Fo > 4s) and 0.1042 (for all data); GOF = 1.171. The space group
choice was confirmed using the CALC MISSYM option of PLATON (A. L.
Spek, J. Appl. Crystallogr., 1988, 21, 578) as no extra crystallographic
symmetry was detected. CCDC 182/684.
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C. L. Bowes, Adv. Mater., 1996, 8, 13.
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765.
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Fig. 3 The crisscrossing of orthogonal pairs of 2/1 helices in [Ag(1)2]SbF6
2. (a) Pairs of intertwined helices crisscross to afford fourfold inter-
penetration. Fourfold interpenetration is indicated by the arrow, which
highlights a yellow–red–blue–green sequence of silver(i) ions (balls).
Orthogonal helices are of opposite handedness. This point is clarified on the
right. (b) Two orthogonal pairs of helices separated to reveal mirror
symmetry. The blue and yellow helices are left-handed and the red and
green helices are right-handed.
along the same direction, a non-polar structure could have
formed. Such a packing of helices was observed in the sheet
Received in Columbia, MO, USA, 18th June 1997; Revised Manuscript
received 17th October 1997; 7/07574J
14
Chem. Commun., 1998