Multicenter bonding and the structure of electron-rich molecules. Model of three-center four-electron bonding reconsidered

Abstract

The concept of three-center four-electron (3c-4e) bonding, which has often been invoked in attempts to interpret the electronic structure of electron-rich molecules, is scrutinized using various methodologies, including generalized population analysis and the analysis of the so-called domain-averaged Fermi holes. Results for representative examples show clearly how manifestations of the 3c-4e model can depend critically on the quality of the wave function being analyzed. In general, the “existence” of 3c-4e bonding tends to be most compatible with the analysis of wave functions of lower quality; enhancements to the flexibility of the basis and/or the inclusion of electron correlation can lead to dramatic changes, such that the 3c-4e scheme transforms into a pattern of two more or less normal, albeit often very polar, two-center two-electron bonds.