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

The reaction of Schiff base 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene (L) with either NiCl₂·6H₂O or Pd^IICl₂(CH₃CN)₂]/NaBF₄] in 1?:?1 stoichiometry yielded mononuclear ionic complexes, trans-Ni^II(L)(H₂O)₂]Cl₂·3H₂O (1·3H₂O) and Pd^II(L)]BF₄]₂ (2), respectively; the reaction of L with Pd^IICl₂(CH₃CN)₂] in 1?:?2 ratio yielded dinuclear cis-Pd^II ₂(μ-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 Pd^II. Complex 1 has distorted octahedral geometry around Ni^II and an extended hydrogen-bond network; distorted square planar geometry around Pd^II in 2 and 3 was observed.