G2(MP2) molecular orbital study of the substituent effect in the H3BPH3-nFn (n=0-3) donor-acceptor complexes

The complexation energies of H3BPH3-nFn (n = 0-3) and the proton affinities of PH3-nFn compounds have been investigated at the G2(MP2) level of theory . G2(MP2) results show that the successive fluorine substitution on the pho sphine increases the stability of H3BPH3-nFn complexes although the basicit y of the PH3-nFn ligands reduces with this substitution. The NBO partitioni ng scheme shows that this stability was related to the hyperconjugation eff ect. It proves also that the shortening of the P-H and P-F bond lengths, up on complexation, is due to an increasing 's' character in these bonds. (C) 2000 Elsevier Science B.V. All rights reserved.