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

摘要

For the 2-electron 3-centre valence bond structure Y center dot A center dot B with an S=0 spin (Psi(ya))(1)(Psi(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 Y: A B and Y A : B. The bond properties for Y center dot A center dot B are shown to be similar to those for the previously-studied 4-electron 3-centre valence-bond structure (Y) over circle center dot A center dot(B) over circle 6, whose V,(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. (c) 2005 Elsevier B.V. All rights reserved.