Using (FH)2 and (FH)3 to Bridge the σ-Hole and the Lone Pair at P in Complexes with H2XP, for X=CH3, OH, H, CCH, F, Cl, NC, and CN

Ab initio MP2/aug′-cc-pVTZ calculations are used to investigate the binary complexes HXP:HF, the ternary complexes HXP:(FH), and the quaternary complexes HXP:(FH), for X=CH, OH, H, CCH, F, Cl, NC, and CN. Hydrogen-bonded (HB) binary complexes are formed between all HXP molecules and FH, but only HFP, HClP, and H(NC)P form pnicogen-bonded (ZB) complexes with FH. Ternary complexes with (FH) are stabilized by F-HP and F-HF hydrogen bonds and FP pnicogen bonds, except for H(CH)P:(FH) and HP:(FH), which do not have pnicogen bonds. All quaternary complexes HXP:(FH) are stabilized by both F-HP and F-HF hydrogen bonds and PF pnicogen bonds. Thus, (FH) with two exceptions, and (FH) can bridge the σ-hole and the lone pair at P in these complexes. The binding energies of HXP:(FH) complexes are significantly greater than the binding energies of HXP:(FH) complexes, and nonadditivities are synergistic in both series. Charge transfer occurs across all intermolecular bonds from the lone-pair donor atom to an antibonding σ∗ orbital of the acceptor molecule, and stabilizes these complexes. Charge-transfer energies across the pnicogen bond correlate with the intermolecular P-F distance, while charge-transfer energies across F-HP and F-HF hydrogen bonds correlate with the distance between the lone-pair donor atom and the hydrogen-bonded H atom. In binary and quaternary complexes, charge transfer energies also correlate with the distance between the electron-donor atom and the hydrogen-bonded F atom. EOM-CCSD spin-spin coupling constants J(F-P) across F-HP hydrogen bonds, and J(P-F) across pnicogen bonds in binary, ternary, and quaternary complexes exhibit strong correlations with the corresponding intermolecular distances. Hydrogen bonds are better transmitters of F-P coupling data than pnicogen bonds, despite the longer FP distances in F-HP hydrogen bonds compared to PF pnicogen bonds. There is a correlation between the two bond coupling constants J(F-F) in the quaternary complexes and the corresponding intermolecular distances, but not in the ternary complexes, a reflection of the distorted geometries of the bridging dimers in ternary complexes. Hydrogen and pnicogen bonding is investigated for binary, ternary and quaternary complexes of the type HXP:(FH). (FH) and (FH) can bridge the lone pair and the σ-hole at P in complexes HXP:(FH), thereby stabilizing these complexes by forming F-HP and F-HF hydrogen bonds and PF pnicogen bonds.This work was carried out with financial support from the Ministerio de Econom a y Competitividad (Project No. CTQ2012-35513- C02-02 and CTQ2015-63997-C2-2-P) and Comunidad Autûnoma de Madrid (Project FOTOCARBON, ref. S2013/MIT-2841). Thanks are also given to the Ohio Supercomputer Center and CTI (CSIC) for their continued computational support. The authors declare no competing financial interest.Peer Reviewe