A-atom valence for the 2-electron 3-centre valence bond structure

Abstract

For the 2-electron 3-centre valence bond structure ▪ with an S=0 spin ( ψ ya ) 1( ψ ab ) 1 configuration, it is deduced that the maximum value for the A-atom valence, V a = V ay + V ab , is 1.155 when AO overlap integrals are omitted. Therefore, the A-atom can exhibit ‘increased-valence’ relative to the A-atom in either of the Lewis structures ▪ and ▪. The bond properties for ▪ are shown to be similar to those for the previously-studied 4-electron 3-centre valence-bond structure ▪, whose V a (maximum) is also 1.155 (R.D. Harcourt, J. Mol. Struct. (THEOCHEM) 684 (2004) 167). For both structures, the one-electron bonds are ‘pseudo’ one-electron bonds, i.e. the values of either or both of their A-atom valencies V ay and V ab can exceed 0.5.