Metal α, ω dicarboxylate complexes.: 4.: Effect of N-donor substitutions on the polymeric network in cobalt(II) hexanedioate complexes:: synthesis and single crystal X-ray investigations

Three cobalt (II)hexanedioate complexes [Co(H2O)(4)(H2L)]n 1 [(H2L=hexanedioic acid), Co(imidazole)(4) (H2L)]n 2 and [Co(pyridine)(2)(H2O)(4)][H2L] 3 are synthesized and structurally characterized to study the effect of N-donor substituents coordinated to the metal center on the polymeric network. Complex 1 is an extended linear polymer; Co(H2O)(4) units are linked: by the monodendate carboxylate from either end of the extended deprotonated hexanedioic acid. There are intra- and interchain I-I-bonding interactions between the coordinated water molecules and the end carboxylate O atoms, the uncoordinated O atom creates two dimensional hydrogen bonding pattern. Complex 2 also is a linear polymer; Co(imidazole), units are linked by monodentate dibasic acid at the either end but with "S" shaped conformation of the hexanedioic acid, not as fully extended as in 1. The effect of bulkier N-donor substitution is seen in the distortion of the octahedral coordination polyhedron of Co(II). The noncordinated carboxylate oxygen makes one intra and one interchain H-bonding interaction with the imidazole N-H group making a two-dimensional I-I-bonded network as in 1. In 3 with the two strong N-donor pyridines coordinated to the metal center, the hexanedioate is out of the coordination sphere and acts as a counter ion. The Co(pyridine)(2)(H2O)(4) units are linked by H-bonding in both the dimensions by extensively folded adipate dianion forming a sheet structure parallel to ab plane. According to our knowledge this is the first example showing a strong H-bonding network in which a tetraaquaCo(II) center forms an eight-membered ring with bidendate H-bonding interactions. None of the coordination polymeric structures form any channels in their molecular packing, even to include a small entity as a water molecule. (C) 1999 Elsevier Science Ltd. All rights reserved.