Computational Study of Benzaldehyde Thiosemicarbazone

DOI : http://dx.doi.org/10.13005/msri/031a04

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Benzaldehyde thiosemicarbazone, C8H9N3S crystals are rectangular plate-like ortho-rhombic structure. The compound undergoes complexation with transition metal ions. Experimental X-ray data of this compound is available which promoted us to study its theoretical parameters like bond length, bond angle, electron density, and general thermodynamic parameters using AM1, PM3, MNDO semi-empirical and 3-21G, 6-31G, and STO-3G ab-initio methods. For bond lengths, the correlation coefficient obtained for AM1, PM3, MNDO methods are 0.921, 0.929, 0.945 and for 3-21G, 6-31G, STO-3G methods are 0.984, 0.983, 0.906 respectively. Out of the three semi-empirical methods MNDO produces most satisfactory correlation (CC=0.945) between experimental and calculated bond length. In the case of bond angles, correlation coefficients are 0.423, 0.363, 0.551 for AM1, PM3, MNDO methods and for 3-21G, 6-31G, STO-3G methods the correlation coefficients are 0.547, 0.418 and 0.612 respectively. Thus for bond angles MNDO and STO-3G methods give most satisfactory correlation (cc=0.551, 0.612). Electronic charge and atom electron density data reveal the coordination sites of benzaldehyde thiosemicarbazone when it undergoes complexation with transition metal ions. Out of three nitrogen atoms N (9) thioamide nitrogen carried more electron density. Thus, performance of semi-empirical AM1, PM3, MNDO and 3-21G, 6-31G, STO-3G ab-initio methods has been tested to find the best auxiliary tool for geometry & electron densities.

Benzaldehyde thiosemicarbazone; Semi-empirical methods