The sign and magnitude of2hJ(F,F) and1hJ(F,H) in FH⋯FH. A CLOPPA analysis of their distance dependence

Abstract

The sign change of the intermolecular 2hJ(F,F) coupling in the (HF)2 dimer as a function of the F-F distance is discussed by means of the CLOPPA method. It is found that it is due to the competition of positive and negative contributions involving the interaction of the σ lone pair of the acceptor nucleus with vacant molecular orbitals localized in the F-H⋯F moiety and with other molecular orbitals localized in the donor molecule. The origin of the sign of each contribution is fully determined by analyzing the response of the electronic system to the magnetic perturbation at the acceptor F nucleus. 2hJ(F,F) coupling in the FH⋯F -, which is positive for all F-F distances, is also analyzed in order to look for the differences with the former case. © 2006 American Chemical Society.