Synthesis and structural characterization of mono- and dinuclear NiII and PdII complexes derived from the tetradentate 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene ligand.

The reaction of Schiff base 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene (L) with either NiCl26H2O or [PdIICl2(CH3CN)2]/Na[BF4] in 1?:?1 stoichiometry yielded mononuclear ionic complexes, trans-[NiII(L)(H2O)2]Cl23H2O (13H2O) and [PdII(L)][BF4]2 (2), respectively; the reaction of L with [PdIICl2(CH3CN)2] in 1?:?2 ratio yielded dinuclear cis-[PdII 2(?-L)Cl4] (3). Complexes 1?3 were characterized by vibrational spectroscopy and X-ray diffraction; diamagnetic 2 and 3 were also characterized by NMR in solution. The molecular structures of 1 and 2 displayed tetradentate coordination of L with formation of two five-membered and one six-membered chelate rings for both complexes. In 3, L showed bidentate coordination mode for each pyridylimine toward PdII. Complex 1 has distorted octahedral geometry around NiII and an extended hydrogen-bond network; distorted square planar geometry around PdII in 2 and 3 was observed.