Preparation, Structure, Photoluminescent and Semiconductive Properties, and Theoretical Calculation of a Mononuclear Nickel Complex with 3-Hydroxy-2- Methylquinoline-4-Carboxylato Ligand

A novel nickel complex with mixed ligands [Ni(L) 2 (EtOH) 2 (MeOH) 2 ] (HL = 3-hydroxy-2-methylquinoline-4-carboxylic acid) has been synthesized through solvothermal reaction and its crystal structure was determined by single-crystal X-ray diffraction technique. Single-crystal X-ray diffraction analyses reveals that the title compound crystallizes in the triclinic system of the P –1 space group, and exists as isolated mononuclear complex. The intermolecular hydrogen bonds lead to the formation of chains, and the layered supramolecular structure is formed by the strong π×××π stacking interactions. Solid-state photoluminescent characterization reveals that the title compound has an emission in the green region. Time-dependent density functional theory (TDDFT) calculation shows that the nature of the photoluminescence of the title compound originates from the ligand-to-ligand charge transfer (LLCT; from the HOMO of the p-orbital of ligand HMCA to the LUMO of the oxygen atoms). A wide optical band gap of 2.25 eV is found by the solid-state UV/vis diffuse reflectance spectrum.