Fig. 1 Representation of the assembling core based on the coordination of
CoCl2 complex by two consecutive ligands 1 which by translation leads to
the directional 1-D network.
Compound 7 was obtained in two steps upon treatment at r.t. of
4-bromopyridine hydrochloride by 2-methyl-3-butyn-2-ol in
the presence of (PPh3)2PdCl2 and CuI in diethylamine affording
compound 8 and the removal of the protecting group by
treatment under reflux with NaOH in toluene.12
Upon slow diffusion at r.t. of a MeOH solution containing
CoCl2·6H2O (8 mg, 6.1 mmol) into a CH2Cl2 solution of
compound 1 (8 mg, 3.3 mmol), purple crystals were obtained
after three weeks. A single-crystal X-ray study† showed the
following relevant features: the crystal (orthorhombic) was
composed of 1, CoCl2 and MeOH molecules. As expected, a
directional 1-D neutral network based on the interconnection of
CoCl2 units by the ligand 1 is observed. The assembling core is
a distorted octahedral Co(II) complex for which the coordination
sphere is composed of two Cl2 anions, two nitrogen and two
sulfur atoms. The two Cl2 anions are located at axial positions
with a Co–Cl distance of 2.425 Å and a Cl–Co–Cl angle of
178.8°. The square base of the octahedron is composed of one
pyridine and one NS2 coordination set belonging to the
tridentate moiety of the ligand with Co–N and Co–S distances
of 2.118 Å and 2.490 Å respectively. Whereas the ClCoS angle
varies from 85° to 95°, the ClCoN angle is ca. 90° and the
NCoN angle is 180.0°. Dealing with the ligand 1, the two
pyridine units are almost untilted and the CC triple bond
distance is 1.207 Å (Fig. 1).
Owing to the unsymmetrical nature of the ligand 1 and, thus,
the assembling core, upon a single translation a 1-D directional
coordination network is indeed obtained. In the crystalline
phase, in principle, a directional 1-D network may either be
packed in centrosymmetric (Fig. 2a) or non-centrosymmetric
modes (Fig. 2b). In the case reported here, the directional
networks are positioned in a parallel fashion but oriented in
opposite directions, thus generating centres of symmetry.
Consequently, the overall system is non-directional (Fig. 3).
This centrosymmetric packing may be due to cancellation of
dipolar moments.
Fig. 3 A portion of the X-ray structure of the directional 1-D network
showing the packing of consecutive networks in ‘head to tail’ fashion. H
atoms and solvent molecules are not presented for clarity. For distances and
angles see text.
However, the 1-D networks were packed parallel to each other
with opposite orientation of linear arrays. The possibility of
controlling the unsymmetrical packing of such 1-D coordina-
tion networks is currently under exploration using chiral
analogues of the ligand 1.
We thank the CNRS and the Institut Universitaire de France
(IUF) for financial support.
Notes and references
† Crystal data for 1: (purple, 173 K), C16H16Cl2CoN2S2·2CH3OH, M =
494.37, orthorhombic, a = 13.3874(4), b = 13.9184(7), c = 12.0950(7) Å,
U = 2253.7(3) Å3, Z = 4, space group Pbcn, Dc = 1.46 g cm23, Nonius
Kappa CCD, Mo-Ka, m = 1.199 mm21, 1739 data with I > 3s(I), R =
0.036, Rw = 0.075. The structural determination was achieved using the
Nonius OpenMolenN package.13 CCDC 182/1762. See http://www.rsc.org/
suppdata/cc/b0/b006099m/ for crystallographic files in .cif format.
1 R. Robson, in Comprehensive Supramolecular Chemistry Vol. 6, ed.
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In conclusion, the unsymmetrical ligand 1 based on two
different coordination poles was shown to form a directional
1-D coordination network in the presence of CoCl2 demonstrat-
ing the viability of the approach. The network was structurally
characterised by X-ray diffraction methods on single crystals.
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Fig. 2 Schematic representation of consecutive directional 1-D networks
leading to symmetrical (a) or unsymmetrical (b) packing.
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Chem. Commun., 2000, 1863–1864