Nature of the Bonding in the Bifluoride Anion, FHF

The nature of the bonding in the bifluoride anion, FHF^-, has long been a topic of discussion with little resolution. A recent (2021) spectroscopic-theoretical study concluded that the bonds in this molecule represent a "crossover from hydrogen to chemical bonding." Spin-coupled generalized valence bond (SCGVB) theory is an advanced orbital theory that describes a broad range of molecules and molecular processes, and its application has provided valuable insights in the electronic structure of many molecules with "unusual" bonding motifs. SCGVB calculations on the FHF^- anion indicate that the bonding in this molecule cannot be attributed to a traditional hydrogen bond or a traditional covalent bond. Instead, the bonds in FHF^- represent a new bonding motif-two polarized, delocalized F^- anions held together by a positively charged hydrogen atom, i.e., the bonding resembles that for a proton-bound anion pair.