What Makes the Trifluoride Anion F3‐ So Special? A Breathing‐Orbital Valence Bond ab initio Study.

Abstract

The ground states of the F3- and H3- hypercoordinated anions are investigated and analyzed in terms of valence bond structures by means of the breathing-orbital valence bond method. While H3- is described reasonably well as the interplay of two major Lewis structures, H2 + H- and its mirror image, the description of F3- requires a further structure, of the type F•F-F•, which strongly stabilizes the trimer relative to the dissociation products, and endows the F3- ground state with a predominant three-electron bond character. It follows that the simple picture that is closest to the true nature of F3- is a resonating combination of F2- + F• and its mirror image. This peculiarity of the F3- electronic structure is at the origin of its preferred dissociation channel leading to F2- + F• rather than to the most stable product F2 + F-, at high collision energies. The three-electron bond character of F3- is also the root cause for the failure of the Hartree−Fock and density functional methods for this species, an...