Theoretical studies of group 1 metal complexes with hydrogen fluoride, M(HF)n, M = Li, Na, and K: a new type of electrides

Small clusters of group 1 metal complexes with hydrogen fluoride molecules M(HF)n, M = Li, Na, and K, are studied with the ab initio molecular orbital method. The trimer M(HF)3 forms a C3v cluster, in which the metal atom is ionized and the ejected electron is trapped on the top of three equivalent HF molecules. The optimized geometric structure of Li(HF)3 is almost identical with that of the ion pair Li+(HF)3Cl- by replacing a Cl- anion with an ejected electron {e-}; thus Li(HF)3 can be described as Li+(HF)3{e-}. The entity {e-} is trapped under the electrostatic field created by three HF bond dipoles; and at the same time, the HF bonds are polarized and weakened. A triplet anion {e-}(HF)3Li+(HF)3{e-} is stable and is a possible anion unit of electrides.