An unprecedented 3D coordination network composed of two intersecting helices

Article abstract of DOI:10.1039/a905009d

A hydro(solvo)thermal reaction between Zn(ClO₄)₂·6H₂O and Z-3-(4-cyanostyryl)pyridine affords an unprecedented chiral 3D coordination polymer Zn(Z-[4-2-(3-pyridyl)ethenyl]benzoate)₂·0.5H₂O with two intersecting six-fold helices, which shows a modest SHG activity owing to the essentially non-conjugate nature of the bridging ligand.

Full text of DOI:10.1039/a905009d

An unprecedented 3D coordination network composed of two intersecting
helices
Owen R. Evans, Zhiyong Wang and Wenbin Lin*
Department of Chemistry, Brandeis University, Waltham, MA 02454, USA. E-mail: wlin@brandeis.edu
Received (in Columbia, MO, USA) 22nd June 1999, Accepted 9th August 1999
A hydro(solvo)thermal reaction between Zn(ClO4)2·6H2O
and Z-3-(4-cyanostyryl)pyridine affords an unprecedented
chiral 3D coordination polymer Zn{Z-[4-2-(3-pyridyl)ethe-
nyl]benzoate}2·0.5H2O with two intersecting six-fold helices,
which shows a modest SHG activity owing to the essentially
non-conjugate nature of the bridging ligand.
Chiral coordination networks are of great interest because of
their potential utility in second-order nonlinear optical (NLO)
applications,1 chiral separations, and asymmetric catalysis.2
Fig. 1 Coordination geometry in 1 of Zn1 and Zn2 centers. The ellipsoids
represent zinc centers, while the circles with increasing sizes represent C, N
Among many chiral structural motifs,3 helices are of particular
interest owing to their structural similarity to nucleic acids.4 The
chirality of such complexes has also shown potential in
asymmetric catalysis.2 We recently demonstrated the construc-
tion of acentric and chiral square grids using bifunctional trans-
pyridylethenylbenzoate linking ligands.1 In contrast, we believe
that steric interactions in cis-pyridylethenylbenzoate will cause
the pyridyl and phenyl group to significantly deviate from
coplanarity. Such ‘skewing’ of coordination sites in the cis-
pyridylethenylbenzoate should favor the formation of a helical
structure. Herein we wish to report the synthesis and character-
ization of an unprecedented chiral 3D network resulting from
the crosslinking of two distinct helices, Zn{Z-[4-2-(3-pyr-
idyl)ethenyl]benzoate}2·0.5H2O, 1.
and O, respectively. Zn1–O distances: 2.084(4), 2.086(5), 2.319(5), and
2.335(5) Å; Zn2–O distances: 1.954(4) and 1.956(4) Å. The Zn–N distances
range from 2.03 to 2.08 Å.
center adopts a tetrahedral geometry by coordinating to the
carboxylate groups of Z-L1 and Z-L2 in a monodentate fashion
and to the pyridyl nitrogen atoms of Z-L3 and Z-L4.
The Zn1 and Zn2 centers are bridged by Z-L3 and Z-L4 to
form an infinite sixfold helix parallel to the c axis (the Zn–Zn
separations are 12.15 and 12.16 Å, respectively). The helices
directed by the Z-L3 and Z-L4 are of the right-handed screw type
and will be referred to as the primary helix (Fig. 2). The primary
helix has a helical period of 44.18 Å, and each helical repeat
contains three Zn1 and three Zn2 centers.
Conformationally similar Z-L1 and Z-L2 ligands serve to link
Zn1 centers of a primary helix to Zn2 centers of adjacent
primary helices. Each primary helix is covalently linked to six
Compound 1 was obtained in 60.5% yield by treating
Zn(ClO4)2·6H2O and Z-3-(4-cyanostyryl)pyridine under hydro-
(solvo)thermal conditions [eqn. (1)].5,6† The IR spectrum of 1
shows two strong symmetric CNO stretches at 1361 and 1400
cm21, suggesting both monodentate and bidentate coordination
of the carboxylate groups.7 The formulation of 1 is supported by
elemental analysis and thermogravimetric analysis results.8
A single crystal X-ray diffraction study of 1‡ reveals an
infinite 3D coordination polymer consisting of two distinct
crosslinked helices. Compound 1 crystallizes in the chiral space
group P32. The basic building block of 1 contains two
crystallographically nonequivalent Zn atoms, four Z-
[4-2-(3-pyridyl)ethenyl]benzoate (Z-L) ligands, and one sol-
vated water molecule (Fig. 1).9 The four Z-L ligands adopt two
drastically different confirmations: the Z-L1 and Z-L2 ligands
are similar with a dihedral angle of 47.2 and 4.75° between the
phenyl and pyridyl rings, while the dihedral angles for the Z-L3
and Z-L4 ligands are 70.3 and 70.1°. The Zn1 center adopts a
cis-octahedral configuration by coordinating to the carboxylate
groups of Z-L3 and Z-L4 in a semichelating fashion and to the
pyridyl nitrogen atoms of Z-L1 and Z-L2. In contrast, the Zn2
Fig. 2 A view of the cross-link between a primary helix and a secondary
helix in 1 as shown down (a) the (111) face and (b) the c axis. The open
bonds represent the primary helix,while the filled bonds represent the
secondary helix. For clarity, the Z-L1 and Z-L2 ligands have been omitted in
(b).
Chem. Commun., 1999, 1903–1904
1903

‡ Crystal data for 1: trigonal, space group P32, a = 9.865(1), c = 44.179(2)
Å, U = 3723.2(3) Å3, Z = 6, Dc = 1.40 g cm23, T = 173 K, Mo-Ka
radiation (l = 0.71073 Å), m = 10.3 cm21. Least-squares refinement based
on 4589 reflections with I > 2s(I) and 643 parameters led to convergence,
with a final value of R1 = 0.045, wR2 = 0.098, and goodness of fit = 0.82.
Flack parameter = 20.033(14). CCDC 182/1378.
1 (a) W. Lin, O. R. Evans, R.-G. Xiong, Z. Wang and G. K. Wong, Angew.
Chem., Int. Ed., 1999, 38, 536; (b) W. Lin, O. R. Evans, R.-G. Xiong and
Z. Wang, J. Am. Chem. Soc., 1998, 120, 13 272; (c) C. Janiak, T. G.
Scharmann, P. Albrecht, F. Marlow and R. Macdonald, J. Am. Chem.
Soc., 1996, 118, 6307; (d) H. Zhang, X. Wang and B. K. Teo, J. Am.
Chem. Soc., 1996, 118, 11 813.
2 D. A. Evans, K. A. Woerpel and M. J. Scott, Angew. Chem., Int. Ed.
Engl., 1992, 31, 430; H. Yamamoto, N. Murase and K. Maruoka, J. Org.
Chem., 1993, 58, 2938.
3 M. J. Zaworotko, Chem. Soc. Rev., 1994, 283; C. Janiak, Angew. Chem.,
Int. Ed. Engl., 1997, 36, 1431; O. M. Yaghi, H. Li, C. Davis, D.
Richardson and T. L. Groy, Acc. Chem. Res., 1998, 31, 474; S. R. Batten
and R. Robson, Angew. Chem., Int. Ed., 1998, 37, 1461.
4 H. Lodich, D. Baltimore, A. Berk, S. L. Zipursky, P. Matsudaira and J.
Darnell, Molecular Cell Biology, Scientific American Books, New
York, 5th edn., 1995.
5 Z-3-(4-cyanostyryl)pyridine was prepared in 27% yield by a room-
temperature Wittig reaction between (4-cyanobenzyl)triphenylphos-
phonium bromide and 3-pyridinecarboxaldehyde with NaOH as the
base in dichloromethane. The product was purified by silica gel column
chromatography [hexane–ethyl acetate (1+1)].
6 The slow hydrolysis of a cyanopyridine precursor to the desired
pyridinecarboxylate ligand has been shown to be the key for the
construction of polymeric coordination networks.1b Also see: O. R.
Evans, Z. Wang, R.-G. Xiong, B. M. Foxman and W. Lin, Inorg. Chem.,
1999, 38, 2969.
Fig. 3 A perspective view of 1 slightly away from the c axis showing the 3D
network resulting from the crosslinking of primary helices with secondary
helices. Only Zn atoms are shown. The primary helices are represented as
open bonds, while the secondary helices are represented as filled bonds.
neighboring primary helices. The Zn–Zn separations (7.47 and
7.49 Å) along the Z-L1 and Z-L2 bridges are significantly shorter
than those along the Z-L3 and Z-L4 bridges. More interestingly,
the connectivity propagated by Z-L1 and Z-L2 results in the
formation of a secondary sixfold helix parallel to the c axis [Fig.
2(b)]. The secondary helix is of the left-handed screw type and
crosslinks the primary helices to afford an infinite 3D network
(Fig. 3).
Many discrete helical structures10 and infinite helical coor-
dination polymers11 have been synthesized over the past
decade. In some of these helical structures, neighboring helices
are connected to each other via crosslinking to form 3D
networks.12 However, the structure of 1 is unprecedented in that
the ‘crosslinks’ (the secondary helices) in 1 also display a
helical-type structure. Both Zn1 and Zn2 centers in 1 are
rendered chiral via coordination to the carboxylate and pyridyl
functionalities of the bridging ligands. Linking of chiral repeats
units into a non-interpenetrated network has thus ensured the
bulk chirality of 1. Preliminary Kurtz powder second harmonic
generation (SHG) measurements13 indicated that 1 exhibits an
expected modest powder SHG efficiency (I2w = 6 vs. a-quartz)
because of the non-conjugate nature of the Z-L ligand. Future
work is directed toward the synthesis of efficient NLO materials
via the incorporation of highly conjugated linking ligands.
We acknowledge NSF (CHE-9727900 and CHE-9875544)
and ACS–PRF for financial support. We also thank Dr Scott R.
Wilson and the Materials Chemistry Laboratory at University of
Illinois at Urbana-Champaign for X-ray data collections.
7 R. C. Mehrotra and R. Bohra, Metal Carboxylates, Academic Press,
New York, 1983.
8 Thermogravimetric analyses indicated a 1.7% weight loss in the range
130–240 °C for 1 (1.7% expected for the loss of one half of water
molecule per formula unit).
9 The solvated water molecule (O9) is ca. 3.5 Å away from both O1 and
O3.
10 J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield, B. Chevrier and D.
Moras, Proc. Natl. Acad. Sci. USA, 1987, 84, 2565; J.-M. Lehn and A.
Rigault, Angew Chem., Int. Ed. Engl., 1988, 27, 1095; U. Koert, M. M.
Harding and J.-M. Lehn, Nature (London), 1990, 346, 339.
11 M. W. Hosseini, C. Kaes, C. E. F. Rickard, B. W. Skelton and A. H.
White, Angew. Chem., Int. Ed., 1998, 37, 920; M. J. Zaworotko, C.
Seward and K. Biradha, Angew. Chem., Int. Ed., 1999, 38, 492; G. Ciani,
L. Carlucci, D. W. Gudenberg and D. M. Proserpio, Inorg. Chem., 1997,
36, 3812; L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, Inorg.
Chem., 1998, 37, 5941; R. W. Saalfrank, M. Decker, F. Hampel, K.
Peters and H. G. Schnering, Chem. Ber., 1997, 130, 1309; X.-T. Wu, B.
Wu, W.-J. Zhang, S.-Y. Yu and X.-T. Wu, J. Chem. Soc., Dalton Trans.,
1997, 1795.
12 R. C. Haushalter, J. Zubieta, V. Soghomonian, Q. Chen and C. J.
O’Connor, Science, 1993, 259, 1596; R. Robson, B. F. Hoskins and
S. R. Batten, Angew. Chem., Int. Ed. Engl., 1997, 36, 636; M. R.
Sundberg, R. Kivekas and J. K. Koskimies, J. Chem. Soc., Chem.
Commun., 1991, 526; R. Robson, B. F. Hoskins, H. Hamit, S. R. Batten
and B. F. Abrahams, Chem. Commun., 1996, 1313; M. Munakata, L. P.
Wu, T. Kuroda-Sowa, M. Maekawa, K. Moriwaki and S. Kitagawa,
Inorg. Chem., 1997, 36, 5416.
Notes and references
† Preparation of Zn(C14H10NO2)2·0.5H2O: a heavy walled Pyrex tube
containing a mixture of Zn(ClO4)2·6H2O (0.045 g, 0.125 mmol) and Z-
3-(4-cyanostyryl)pyridine (0.052 g, 0.5 mmol) in methanol (0.2 mL) and
water (0.05 mL) was frozen and sealed under vacuum, and placed inside an
oven at 120 °C. Colorless hexagonal crystals were obtained after 72 h of
heating. Yield (0.040 g, 60.5%). Anal. calc. (found) for C28H21N2O4.5Zn: C,
64.3 (64.1); H, 4.05 (4.04); N, 5.36 (5.59%).
13 S. K. Kurtz, J. Appl. Phys., 1968, 39, 3798.
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