d7/d8 Metal Complexes Constructed from 2,6-Bis(2-benzimidazolyl)pyridyl or 2,6-Di-(pyrazol-3-yl)pyridine Derivatives: Synthesis, Structure, Characterization, and Photocatalytic Activity

By introducing 2,6-bis(2-benzimidazolyl)pyridyl and 2,6-di-(pyrazol-3-yl)pyridine derivatives as ligand in the reaction system, three new transition-metal coordination complexes have been successfully synthesized, namely, [Co(HL1)2] (1), [Ni(HL1)2] (2), and [Ni3(H2L2)2⋅(HL2)2]⋅(OH)3⋅(Ac)⋅H2O (3) (H2L1=2,6-bis(benzimidazol-2-yl)pyridine and H2L2=2,6-di-(5-phenyl-1H-pyrazol-3-yl)pyridine). They are all characterized by elemental analysis, IR spectroscopy, UV absorption spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Structural analysis shows that the structures of complexes 1 and 2 are similar. They are constructed from one metal (Co, Ni) atom and two 2,6-bis(benzimidazol-2-yl)pyridine ligands (HL1−); the HL1− ligand is in the tridentate coordination mode with N3 donors. Complex 3 is a trinuclear Ni complex with four 2,6-di-(5-phenyl-1H-pyrazol-3-yl)pyridine (H2L2) ligands, in which the H2L2 possesses two coordination fashions: terminal tridentate and bridging tetradentate. In addition, the surface photovoltage spectroscopy and photocatalytic activities of complexes 1–3 were investigated in detail. The results reveal that complex 3 possesses higher photocatalytic activity.