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

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.

Graphical abstractA mixed-ligand complex bis-(semicarbazido)dihydrazine nickel(II) has been synthesized by unusual ring opening of uracil with hydrazine hydrate, and characterized by IR, UV–Vis spectroscopy and X-ray diffraction study. The structure has been satisfactorily modeled by DFT calculations. Electronic spectrum of complex has been analyzed in depth with the help of TDDFT.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Semicarbazide formed by ring opening reaction of uracil with hydrazine and Ni(II) results a crystalline complex. ► Bis-(semicarbazido)dihydrazine nickel(II) is characterized by spectral and X-ray studies. ► DFT computation is used to correlate experimental results with calculated data. ► TDDFT calculations interpret UV–Vis spectral bands for high-energy ILCT and low energy LMCT.