Solvatochromism in mixed-chelate of copper(II) with tetramethyl ethylenediamine and 2,4-dihydroxybenzophenone, experimental and computational study

Abstract

A mixed-chelate copper(II) complex, [Cu(dhbp)(tmeda)(H2O)]ClO4, where dhbp = 2,4-dihydroxybenzophenone and tmeda = tetramethyl ethylenediamine, was synthesized and characterized using various techniques including elemental analysis, molar conductance, UV-Vis, IR spectroscopy, and computational study. The solvatochromic behavior of the complex was investigated by visible spectroscopy, revealing positive solvatochromism. To understand the interaction mechanism between the complex and solvent, six standard solvent parameters (DN, AN, α, β, π*, and ET(30)) were assigned using the stepwise multiple linear regression (SMLR) method. Statistical analysis indicated that the DN parameter of the solvent had the most significant contribution in changing the d-d absorption band of the complex. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to study the electronic structure of the complex and gain insights into the solvatochromism processes. The results suggested that the approach of solvent molecules and coordination to the vacant site of the complex led to a change in its geometry from square pyramidal to octahedral. This geometric transformation caused the d-d transition band of the complex to shift towards the red region with increasing solvent DN, thus explaining the observed solvatochromism.