Structural investigations on bis-(semicarbazido)dihydrazine nickel(II) complex synthesized by using uracil and hydrazine hydrate

Abstract

A mixed-ligand bis-(semicarbazido)dihydrazine nickel(II) complex, [Ni(sem)2(Hz)2] (Hsem=semicarbazide, Hz=hydrazine) has been synthesized by unusual ring opening of uracil reacting with hydrazine hydrate in the presence of nickel(II) chloride. The complex was characterized by elemental analyses, IR, UV–Vis spectral studies and magnetic susceptibility measurement. The molecular structure of the complex was finally determined by single crystal X-ray diffraction study. The complex acquires a six coordinate distorted octahedral geometry in which semicarbazide ligand binds through hydrazinic –NH2 and a deprotonated C–O− group whereas, hydrazine coordinates through one of the –NH2 group to nickel(II) centre. The structure was stabilized by the presence of strong inter-molecular hydrogen bonding interactions N–H⋯N and N–H⋯O forming a huge supramolecular network. Further, the structure was satisfactorily modeled by density functional theory calculations (DFT). UV–Vis and IR spectra are analyzed in depth with the help of time dependent-DFT. The theoretical analyses of electronic structure and molecular orbitals have suggested that the high-energy absorption bands in UV–Vis spectrum are mainly π→π∗ ligand-to-ligand charge transfer transitions (LLCT) and lower energy absorption bands are π→(dz2 or dx2−y2, dyz) ligand-to-metal charge transfer transitions (LMCT) in nature.