Anticooperativity of FH···Cl- hydrogen bonds in [FH)n Cl]- clusters (n = 1…6).

The change of cooperativity of FH···Cl- hydrogen bonds upon sequential addition of up to six FH molecules to the Cl- first coordination sphere is investigated. The geometry of clusters [(FH) n Cl]- (n = 1…6) was calculated (CCSD/aug-cc-pVDZ) and compared with [(FH) n F]- clusters. The geometry is determined by the symmetry-driven electrostatic requirements and also by the fact that formation of each new FH···Cl- bond creates a depression in the chlorine's electron cloud on the opposite side of Cl- (σ-hole), which limits the range of directions available for subsequent H-bond formation. The mutual influence of FH···Cl- hydrogen bonds is anticooperative-the addition of each FH molecule weakens H-bonds by 23-16% and decreases their covalent character (as seen by LMO-EDA decomposition and QTAIM analysis). Anticooperativity effects could be tracked by spectroscopic parameters (frequency of local HF mode νFH , chemical shift δH , spin-spin coupling constants 1 JFH , 1h JHCl , 2h JFCl and nuclear quadrupolar constants χ18F , χD , and χ35Cl . © 2019 Wiley Periodicals, Inc.