X-Ray determination of the effective charges on sulfur and phosphorus atoms in chemical compounds

The dependencies of Kα line shifts of the P and S atoms on effective charges of the atoms, calculated by CNDO/S, CNDO/2, INDO, and MNDO methods in the minimal and extended basis sets, have been investigated for model compounds. Good linear relationships between Kα shifts and atomic charges have been obtained for all cases investigated except for CNDO/2 and INDO calculations in the extended basis set. It is found that the PS bond ionicity is a nearly constant value, whereas the P S bond ionicity increases linearly with an increase in the positive charge of the central P atom. It is shown that the P and S atom charge in sulfides and phosphines containing no substituents with a strong M-effect at the central atom depend only on inductive substituent effects. Also, the positive charge on the central atom increases with the growth of the π-donor properties of substituents in sulfides and phosphines containing substituents exerting a strong M-effect, as well as in phosphoryl and thiophosphoryl compounds and sulfones.