Synthesis, spectroscopic and structural characterization of cobalt(II) complex with uracil-containing 2,6-diformylpyridine ligand: Theoretical studies on the ligand and pentagonal-bipyramidal [Co(L)(H2O)2]2+ and [Zn(L)(H2O)2]2+ cations

The title complex, trans-diaqua{5,5′-[(E,E)-pyridine-2,6-diylbis(methylidynenitrilo)]bis-[pyrimidine-2,4(1H,3H)-dione]}cobalt(II) bis(hexafluorophosphate) dihydrate [Co(C15H11N7O4) (H2O)2]·2(PF6)·2(H2O), has been synthesized, and characterized by IR spectroscopy and single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P21/c with a = 10.7301(4) Å, b = 12.0537(3) Å, c = 21.6030(9) Å and β = 109.392 (3)°. In the title complex, the Co2+ centre is seven-coordinated in a slightly distorted pentagonal-bipyramidal geometry, with the two water O atoms located in the apical positions, and the pyridine N atom, the two imine N atoms and two carbonyl O atoms of the uracil groups located in the equatorial plane. The positions of fluorine atoms in the hexafluorophosphate groups were disordered. The charge is balanced by two PF62− anions. In addition to the molecular geometry from X-ray experiment, theoretical studies have been carried out on the structures of the pentagonal-bipyramidal [Co(L)(H2O)2]2+ and [Zn(L)(H2O)2]2+ cations using the Hartree–Fock (HF) and density functional theory (DFT-B3LYP) methods in conjunction with effective core potential basis set (LANL2DZ) to clarify the solid state behaviour of these cations. Besides, frontier molecular orbitals (FMO) analysis and natural bond orbital (NBO) analysis of [Co(L)(H2O)2]2+ cation are presented here together with vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the pentadentate ligand calculated at HF and DFT (B3LYP) levels with 6-31G(d) basis set.