Synthesis, Characterization, and studies of coordination-polymeres with isomeric pyridylcyanoximes: Route to metal ribbons with very short Tl•••Tl separations


Two isomeric pyridylcyanoximes, H(3PCO) and H(4PCO), containing nitrogen atoms of the heterocycle at 3- and 4-positions, respectively, were synthesized and thoroughly characterized using IR (including 15N labeling), UV-visible, 1H, 13C one- and two-dimensional NMR spectroscopy, and X-ray analysis. The H(3PCO) exists as a mixture of syn- and anti-isomers in solutions, contrary to H(4PCO) which is present only as an anti-isomer. Both compounds have planar geometry in the solid state and form elegant zigzag chains via H-bonding between the oxime group and the N-atom of the heterocycle. The H(3PCO) and H(4PCO) upon addition of a base form colored conjugated and solvatochromic anions in solutions. The reaction of the hot aqueous solution of Tl 2CO 3 with solid isomeric pyridylcyanoximes leads to TlL, which were characterized by elemental analyses, IR spectroscopy, and X-ray analysis. Both complexes represent three-dimensional coordination polymers of different complexities where cyanoxime anions act as bridging ligands. Thallium(I) atoms in Tl(3PCO) and Tl(4PCO) form infinite, planar "metal ribbons" with unusually short intermetallic distances: 3.705 Å in Tl(3PCO) and 3.635 Å in Tl(4PCO) respectively, which are close to that in metallic thallium (3.465 Å). The latter compound has the second shortest Tl•••Tl thallophillic interaction reported in the literature thus far. Both yellow Tl(3PCO) and orange Tl(4PCO) are insulators at ambient conditions: R ∼ 1 × 10 11 Ohm.



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Crystal Growth and Design