Synthesis, structure, and surface photovoltage properties of a series of novel d7–d10 metal complexes with pincer N-heterocycle ligands

Abstract

Novel d⁷–d¹⁰ complexes Cu(bpz*eaT)(SCN)₂ (1), Ni(bpz*eaT)(SCN)₂ (2), Co(bpz*eaT)((SCN)₂ (3), [Ni(bpz*eaT)(N₃)]·H₂O (4) and Co(bpz*eaT)(N₃) (5) (bpz*eaT: 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-diethylamino-1,3,5-triazine) were synthesized by the reaction of a metal salt (CuCl₂·2H₂O, NiCl₂·6H₂O, CoCl₂·6H₂O or Co(CH₃COO)₂·4H₂O), pincer N-heterocyclic ligands and KSCN or NaN₃ in either acetonitrile or a mixed solution at different temperatures. The structures of these complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analyses (TG) and single-crystal diffraction analysis. Structural analysis reveals that the metal atoms (Cu and Co) in complexes 1, 3 and 5 are in a five-coordination mode, forming distorted square pyramid geometries with N5 donors; Ni atoms in the complexes 2 and 4 are in a six-coordination mode, forming slightly distorted octahedra with the set of N5S and N6 cores, respectively. In complexes 1–5, the auxiliary N-donor monodentate ligands were only connected with one metal center. In complexes 2 and 4, the two metal centers were connected by bridging coordinated SCN⁻ and N₃⁻, which were different from those in complexes 1, 3 and 5. In addition, surface photovoltage properties of the five complexes have also been studied and discussed in detail. Surface photovoltage spectra (SPS) of the complexes 1–5 show that the surface photovoltage (SPV) response signals increase when the positive electric field is enhanced in the range of 300–800 nm. The results show that these complexes possess potential p-type semiconductor properties and their uses may be extended to semiconductor materials.