Electronegativity equalization and the electronic structure of polyhedral clusters of main-group atoms

Abstract

The concept of the equalization of atomic electronegativities accompanving molecule formation is applied to a study of the electronic structure of polyhedral clusters of main-group atoms such as Ge, Sn, Pb, Tl, and Bi. Emphasis is placed upon charged clusters such as Sn 9−x Pb x 4− (x = 0 → 9), Sn 9-x Ge x 4− , Sn 8−x Pb x Tl 5− , Sn 2 Bi 2 2− , SnTe 4 4− , etc. The role of the relativistic spin-orbit splitting of an np shell into np 1/2 and np 3/2 subshells in modifying atomic and hence molecular electronegativities is discussed. Correlations are made between calculated charge distributions and observed 199 Sn NMR chemical shifts for clusters of a given size and charge. It is concluded that a useful picture of charge distributions in these clusters may be obtained from electronegativity equalization considerations.