Experimental (FT-IR, FT-Raman, and NMR) and DFT studies of the structures and spectral properties of diphenylcarbazone and diphenylthiocarbazone

Abstract

Diphenylcarbazone (DPC) and Dipheylthiocarbazone (DPTC) are widely used analytical reagents for the detection of different metals via the formation of colored complexes. Even though these analytical reagents have been used for decades, their exact structures remain unresolved. In this study, the molecular structures, electronic and spectroscopic properties were systematically investigated to give an insight into the exact structures of DPC and DPTC. FT-IR, FT-Raman and Nuclear Magnetic Resonance spectra of the two compounds were recorded. The results were supported with Density Functional Theory (DFT) calculations using the B3LYP/6-311++G(d,p) method. Torsional energy scans were carried out to determine the minimum configuration of these molecules in their traditional keto/thione forms. The optimized structural parameters of the minimum energy structures were compared with the optimized structures of the symmetrical keto/thione and enol/thiol forms of the molecules. The result revealed that symmetrical keto/thione forms were energetically favoured in the gas phase. The effects of solvent on the conformational preference of the DPC and DPTC were reported. The combination of the experimental and theoretical data gave an insight into the structures of these molecules. Moreover, the result could give a better understanding of the coordination chemistry of these important ligands.