Recoupled-pair bonding and 4-electron 3-center bonding units.

Consideration is given to recoupled-pair bonding and the origin of electronic hypervalence for formulations of the bonding for symmetric 4-electron 3-center ((4e,3c)) bonding units with one overlapping atomic orbital per atomic center. Molecular orbital and valence bond theory for symmetric (4e,3c) bonding units is redescribed and applied to aspects of the bonding for SF(6) and CLi(6). The results of minimal basis set calculations for CLi(6) provide support for a hypothesis that two Li-C-Li (3e,3c) bonding units rather than two (4e,3c) bonding units are preferred for this molecule. Brief comments are also made on the use of [Formula: see text] and [Formula: see text] as valence bond structures for the three electron bond.