Combined experimental-theoretical characterization of chelidamate nickel complex with 4-methylpyrimidine

A new chelidamate complex of nickel(II) ion, [Ni(chel)(H2O)2(mpd)]·2H2O [chel: chelidamate or 4-hydroxypyridine-2,6-dicarboxylate, mpd: 4-methylpyrimidine] was synthesized and characterized by single-crystal X-ray diffraction, UV-Vis and FT-IR spectroscopy. Intermolecular O-H⋯O and O-H⋯N hydrogen bonds and π-π stacking interactions appear to be effective in the stabilization of the crystal structure. Theoretical calculations have been carried out by using Hartree-Fock (HF)/6-31G (d) and Density Functional Theory (DFT)/6-31+G (d). Molecular geometry from X-ray experiment of Ni(II) complex in the ground state was compared using unrestricted hybrid density functional B3LYP. HOMO-LUMO energies, absorption wavelengths and excitation energy were computed by time dependent DFT (TD-DFT) method with polarizable continuum model. The observed FT-IR vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The natural charges on the atoms and second-order interaction energies were derived from natural bond orbital analysis (NBO).