Crystal Structure and Hirshfeld Surface Analysis of Bis(Triethanolamine)Nickel(II) Dinitrate Complex and a Revelation of Its Characteristics via Spectroscopic, Electrochemical and DFT Studies Towards a Promising Precursor for Metal Oxides Synthesis

Metal complexes with chelating ligands are known as promising precursors for the synthesis of targeted metal oxides via thermal decomposition pathways. Triethanolamine (TEA) is a versatile ligand possessing a variety of coordination modes to metal ions. Understanding the crystal structure is beneficial for the rational design of the metal complex precursors. Herein, a bis(triethanolamine)nickel (II) dinitrate (named as Ni-TEA) crystal was synthesized and thoroughly investigated. X-ray crystallography revealed that Ni(II) ions adopt a distorted octahedral geometry surrounded by two neutral TEA ligands via two N and four O coordinates. Hirshfeld surface analysis indicated the major contribution of the intermolecular hydrogen-bonding between -OH groups of TEA in the crystal packing. Moreover, several O-H stretching peaks in Fourier transformed infrared spectroscopy (FTIR) spectra emphasizes the various chemical environments of -OH groups due to the formation of the hydrogen-bonding framework. The Density-functional theory (DFT) calculation revealed the electronic properties of the crystal. Furthermore, the Ni-TEA complex is presumably useful for metal oxide synthesis via thermal decomposition at a moderate temperature (380 degrees C). Cyclic voltammetry indicated the possible oxidative reaction of the Ni-TEA complex at a lower potential than nickel(II) nitrate and TEA ligand, highlighting its promising utility for the synthesis of mixed valence oxides such as spinel structures.