Topological analysis of metal–ligand and hydrogen bonds in transition metal hybrid structures – A computational study

Abstract

The energy minimized structures of transition metal sulfates templated by 2-methylpiperazine, (C5H14N2)[M(SO4)2(H2O)4]·H2O (M=Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+), are obtained at MP2 and M05-2X level of theories by implementing LANL2DZ basis set. The geometrical parameters and vibrational frequencies of (C5H14N2)[M(SO4)2(H2O)4]·H2O (M=Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) complexes are compared with the available X-ray crystallographic results and they are found to agree well with the crystallographic data. Nature of metal–ligand and hydrogen bonds in the transition metal hybrid structures are analyzed by using quantum theory of atoms in molecule [QTAIM] calculations and electron localizability indicator (ELI-D). Polarizable continuum model (PCM) is adopted to study the optimized transition metal structures. The calculated metal-ion affinity and binding energy values correlate well with the ionic radius of metal cations. NBO analysis confirms the charge transfer from monodentate ligands to transition metal cations. Energies of hydrogen bonds are also calculated from the NBO analysis. Topological parameters such as total electron density at the critical point and the core-valence bifurcation index are used as descriptors of hydrogen bond strength. The present calculations provide an important physicochemical insight into the crystal structure of copper sulfate templated by 2-methylpiperazine (C5H14N2)[Cu(SO4)2(H2O)4]·H2O and other metal cations.