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 2 ·6H 2 O in a molar ratio of 2:2:1 was reacted with two equivalents of hydrazine monohydrate in methanol, followed by the addition of aqueous NH 4 PF 6 solution, afforded a Ni II complex with two unsymmetric azine-based ligands, [Ni(HL H ) 2 ](PF 6 ) 2 ( 1 ) or [Ni(HL Me ) 2 ](PF 6 ) 2 ( 2 ), in a high yield, where HL H denotes 2-pyridylmethylidenehydrazono-(4-imidazolyl)methane and HL Me 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 II complexes bearing an unsymmetric HL H or HL Me azines in a tridentate κ 3 N , N' , N" coordination mode. The HL H complex with a methanol solvent, 1 ·MeOH, crystallizes in the orthorhombic non-centrosymmetric space group P 2 1 2 1 2 1 with Z = 4, affording conglomerate crystals, while the HL Me complex, 2 ·H 2 O·Et 2 O, crystallizes in the monoclinic and centrosymmetric space group P 2 1 / n with Z = 4. In the crystal of 2 ·H 2 O·Et 2 O, there is intermolecular hydrogen-bonding interaction between the imidazole N-H and the neighboring uncoordinated azine- N atom, forming a one-dimensional polymeric structure, but there is no obvious magnetic interaction among the intra- and interchain paramagnetic Ni II ions.