Mononuclear and three-dimensional metal complexes based on a multidentate hydrazone ligand.

A potentially pentadentate hydrazone ligand, N'-[1-(pyrazin-2-yl)ethylidene]nicotinohydrazide (HL), was prepared from the condensation reaction of nicotinohydrazide and acetylpyrazine. Reactions of HL with MnCl2, Mn(CH3COO)2 and Cd(CH3COO)2 afforded three metal complexes, namely dichlorido{N'-[1-(pyrazin-2-yl-κN(1))ethylidene]nicotinohydrazide-κ(2)N',O}manganese(II), [MnCl2(C12H11N5O)], (I), bis{N'-[1-(pyrazin-2-yl-κN(1))ethylidene]nicotinohydrazidato-κ(2)N',O]manganese(II), [Mn(C12H10N5O)2], (II), and poly[[(acetato-κ(2)O,O'){μ3-N'-[1-(pyrazin-2-yl-κ(2)N(1):N(4))ethylidene]nicotinohydrazidato-κ(3)N',O:N(1)}cadmium(II)] chloroform disolvate], {[Cd(C12H10N5O)(CH3COO)]·2CHCl3}n, (III), respectively. Complex (I) has a mononuclear structure, the Mn(II) centre adopting a distorted square-pyramidal coordination. Complex (II) also has a mononuclear structure, with the Mn(II) centre occupying a special position (C2 symmetry) and adopting a distorted octahedral coordination environment, which is defined by two O atoms and four N atoms from two N'-[1-(pyrazin-2-yl)ethylidene]nicotinohydrazidate (L(-)) ligands related via a crystallographic twofold axis. Complex (III) features a unique three-dimensional network with rectangular channels, and the L(-) ligand also serves as a counter-anion. The coordination geometry of the Cd(II) centre is pentagonal bipyramidal. This study demonstrates that HL, which can act as either a neutral or a mono-anionic ligand, is useful in the construction of interesting metal-organic compounds.