{1-[1-(2-Hy-droxy-phen-yl)ethyl-idene]-2-(pyridin-2-yl-κN)hydrazine-κ(2)N',O}{1-[1-(2-oxidophen-yl)ethyl-idene]-2-(pyridin-2-yl-κN)hydrazine-κ(2)N',O}nickelate(II) nitrate hemihydrate.

The 2-hydrazino-pyridine precursor has been widely used to prepare ligands of various kinds by condensation with carbonyl compounds. These types of ligands are suitable for synthesizing novel transition metal (II) complexes with inter-esting magnetic properties. In this context we have synthesized the ligand 1-(2-hy-droxy-phenyl-2-ethyl-idene)-2-(pyridin-2-yl)hydrazine (HL) which was used in the preparation of the mononuclear title complex, [Ni(C(13)H(12)N(3)O)(C(13)H(13)N(3)O)]NO(3)·0.5H(2)O. As a result of the presence of HL and L in the [{Ni(HL)(L)}](+) unit, the complex appears to be a supramolecular dimer composed of the Δ(-) and Λ(-) optical isomers, which are linked by strong hydrogen-bonds. As well as the dimer generated by two mononuclear [{Ni(HL)(L)}](+) cations, the asymmetric unit also contains two nitrate anions and one water mol-ecule. Each Ni atom is coordinated to two ligand mol-ecules by a nitro-gen atom of the pyridine ring, an imine nitro-gen atom and a phenolic oxygen atom of one of the ligand mol-ecules and a phenolate oxygen atom of the other organic mol-ecules. The environment around the cation is a distorted octa-hedron. The basal planes are defined by the two nitro-gen atoms of the pyridine rings and the two phenolic oxygen atoms of the ligand, the apical positions being occupied by the azomethine atoms. The O atoms of one of the nitrate ions are disordered over two sets of sites in a 0.745†(9):0.255†(9) ratio. In the crystal, the dimers are linked by numerous hydrogen bonds, forming a three-dimensional framework.