Ab initio calculations on the electronic structure of the divalent lead-water complex.

We studied the electronic structure of the Pb (2+)-4H 2O system. Analysis of the complex orbital evidenced no mixing between the 6s lone pair orbital of the lead and the 6p orbital components. Moreover, we found that the HOMO is widely described by the mixture of the 6p components with the 7s valence orbital of the lead. This orbital shows an important elliptical electron charge density around the lead ion and opposite the direction of the short lead-water bonds. From these results, we demonstrated that the hemidirected conformation of the Pb (2+)-4H 2O system could be easily explained by the shape of the electron charge density distribution of the HOMO rather than by the stereochemically active character of the 6s (2) lone pair of lead electrons.