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 HLwith MnCl2, Mn(CH3COO)2and Cd(CH3COO)2afforded three metal complexes, namely dichlorido{N′-[1-(pyrazin-2-yl-κN1)ethylidene]nicotinohydrazide-κ2N′,O}manganese(II), [MnCl2(C12H11N5O)], (I), bis{N′-[1-(pyrazin-2-yl-κN1)ethylidene]nicotinohydrazidato-κ2N′,O]manganese(II), [Mn(C12H10N5O)2], (II), and poly[[(acetato-κ2O,O′){μ3-N′-[1-(pyrazin-2-yl-κ2N1:N4)ethylidene]nicotinohydrazidato-κ3N′,O:N1}cadmium(II)] chloroform disolvate], {[Cd(C12H10N5O)(CH3COO)]·2CHCl3}n, (III), respectively. Complex (I) has a mononuclear structure, the MnIIcentre adopting a distorted square-pyramidal coordination. Complex (II) also has a mononuclear structure, with the MnIIcentre occupying a special position (C2symmetry) and adopting a distorted octahedral coordination environment, which is defined by two O atoms and four N atoms from twoN′-[1-(pyrazin-2-yl)ethylidene]nicotinohydrazidate (L−) ligands relatedviaa crystallographic twofold axis. Complex (III) features a unique three-dimensional network with rectangular channels, and theL−ligand also serves as a counter-anion. The coordination geometry of the CdIIcentre 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.