Density functional studies of nitrosyl halides, thiazyl halides and related molecules

摘要

Density functional calculations at the B3LYP/6-31G~* level have been performed on a series of nitrosyl (Z-N=O) and thiazyl (Z-S≡N) compounds where Z is F, Cl, Br and H, in order to understand the electronic properties and nature of bonding in these molecules. The energies at the optimized geometries, together with their less stable isomers were calculated and reported. All of the structural isomers studied were found to be minima on the potential energy surface. The energy differences between the isomers are 26.3-43.6 kcal/mol in the nitrosyl series and 13.7-26.2 kcal/mol in the thiazyl series. Based on the frontier molecular orbital (MO) theory and the second order perturbation theory, MO diagrams were constructed to account for the major orbital interactions which chiefly contribute to the stabilization of the molecules. The qualitative approach has shown to be successful in providing insights into the connectives of the atoms, the bond orders and the relative stabilities of the isomers. Simple correlations between the electronegativity of Z and the magnitude of the energy difference between the two isomers have been established.