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

A potentially pentadentate hydrazone ligand, N ′‐[1‐(pyrazin‐2‐yl)ethylidene]nicotinohydrazide (H L ), was prepared from the condensation reaction of nicotinohydrazide and acetylpyrazine. Reactions of H L with MnCl 2 , Mn(CH 3 COO) 2 and Cd(CH 3 COO) 2 afforded three metal complexes, namely dichlorido{ N ′‐[1‐(pyrazin‐2‐yl‐κ N 1 )ethylidene]nicotinohydrazide‐κ 2 N ′, O }manganese(II), [MnCl 2 (C 12 H 11 N 5 O)], (I), bis{ N ′‐[1‐(pyrazin‐2‐yl‐κ N 1 )ethylidene]nicotinohydrazidato‐κ 2 N ′, O ]manganese(II), [Mn(C 12 H 10 N 5 O) 2 ], (II), and poly[[(acetato‐κ 2 O , O ′){μ 3 ‐ N ′‐[1‐(pyrazin‐2‐yl‐κ 2 N 1 : N 4 )ethylidene]nicotinohydrazidato‐κ 3 N ′, O : N 1 }cadmium(II)] chloroform disolvate], {[Cd(C 12 H 10 N 5 O)(CH 3 COO)]·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 H L , which can act as either a neutral or a mono‐anionic ligand, is useful in the construction of interesting metal–organic compounds.