Selective Formation of Unsymmetric Multidentate Azine-Based Ligands in Nickel(II) Complexes.

A mixture of 2-pyridine carboxaldehyde, 4-formylimidazole (or 2-methyl-4-formylimidazole), and NiCl·6HO in a molar ratio of 2:2:1 was reacted with two equivalents of hydrazine monohydrate in methanol, followed by the addition of aqueous NHPF solution, afforded a Ni complex with two unsymmetric azine-based ligands, [Ni(HL)](PF) () or [Ni(HL)](PF) (), in a high yield, where HL denotes 2-pyridylmethylidenehydrazono-(4-imidazolyl)methane and HL is its 2-methyl-4-imidazolyl derivative. The spectroscopic measurements and elemental analysis confirmed the phase purity of the bulk products, and the single-crystal X-ray analysis revealed the molecular and crystal structures of the Ni complexes bearing an unsymmetric HL or HL azines in a tridentate κ, , coordination mode. The HL complex with a methanol solvent, ·MeOH, crystallizes in the orthorhombic non-centrosymmetric space group 222 with Z = 4, affording conglomerate crystals, while the HL complex, ·HO·EtO, crystallizes in the monoclinic and centrosymmetric space group 2/ with Z = 4. In the crystal of ·HO·EtO, there is intermolecular hydrogen-bonding interaction between the imidazole N-H and the neighboring uncoordinated azine- atom, forming a one-dimensional polymeric structure, but there is no obvious magnetic interaction among the intra- and interchain paramagnetic Ni ions.