Nonconventional Hydrogen Bonding between Clusters of Gold and Hydrogen Fluoride

The bonding patterns between small neutral gold Au3 ≤ n ≤ 7 and hydrogen fluoride (HF)1 ≤ m ≤ 4 clusters are discussed using a high-level density functional approach. Two types of interactions, anchoring Au−F and F−H···Au, govern the complexation of these clusters. The F−H···Au interaction exhibits all the characteristics of nonconventional hydrogen bonding and plays a leading role in stabilizing the lowest-energy complexes. The anchor bonding mainly activates the conventional F−H···F hydrogen bonds within HF clusters and reinforces the nonconventional F−H···Au one. The strength of the F−H···Au bonding, formed between the terminal conventional proton donor group FH and an unanchored gold atom, depends on the coordination of the involved gold atom: the less it is coordinated, the stronger its nonconventional proton acceptor ability. The strongest F−H···Au bond is formed between a HF dimer and the singly coordinated gold atom of a T-shape Au4 cluster and is accompanied by a very large red shift (1023 cm-1) of the ν(F−H) stretch. Estimations of the energies of formation of the F−H···Au bonds for the entire series of the studied complexes are provided.