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 P2(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 P2(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.