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 acetyl-pyrazine. Reactions of HL with MnCl2, Mn(CH3COO)(2) and Cd(CH3COO)(2) afforded three metal complexes, namely dichlorido{N'-[1-(pyrazin-2-yl-kappa N-1)ethylidene]nicotinohydrazide-kappa N-2',O}manganese(II), [MnCl2(C12H11N5O)], (I), bis{N'[1-(pyrazin-2-yl-kappa N-1)ethylidene]nicotinohydrazidato-kappa N-2',O]-manganese(II), [Mn(C12H10N5O)(2)], (II), and poly[[(acetato-kappa O-2,O'){mu(3)-N'-[1-(pyrazin-2-yl-kappa N-2(1):N-4)ethylidene]nicotino-hydrazidato-kappa N-3',O:N-1}cadmium(II)] chloroform disolvate], {[Cd(C12H10N5O)(CH3COO)]center dot 2CHCl(3)}(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 (C-2 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.