Electron pairing and chemical bonds: Bonding in hypervalent molecules fromanalysis of Fermi holes

Bonding in the hypervalent molecules SF4, BrF5, PF5, and SF6 was studied us ing multicenter bond order indices and examination of the eigenvalues and t he eigenvectors of the Fermi holes of the constituent atoms. Diagonalizatio n of the Fermi holes provided quantitative validation of Musher's categoriz ation of hypervalency with SF4 and BrF5 representative of type I, and PF5 a nd SF6 belonging to type II. The eigenvalues and eigenvectors of type I mol ecules distinguished between classic two-center two-electron bonds and thre e-center four-electron bonds, whereas the results of diagonalization for ty pe II molecules demonstrated the presence of substantial reorganization of the valence stale of the central atom leading to equivalent bonds and the h ighest expected symmetry of the molecule. (C) 1999 John Wiley & Sons, Inc.