30 June 2000 Ž . Chemical Physics Letters 324 2000 156–160 www.elsevier.nlrlocatercplett ž / G2 MP2 molecular orbital study of the substituent effect in the ž / H BPH F n s 0–3 donor–acceptor complexes 3 3yn n H. Anane a , A. Jarid a , A. Boutalib a, ) , I. Nebot-Gil b , F. Tomas b ´ a Departement de Chimie, UniÕersite Cadi Ayyad, Faculte des Sciences Semlalia, BP 2390 Marrakech, Morocco ´ ´ ´ b ´ ´ Departament de Quimica-Fisica, UniÕersitat de Valencia, Dr. Moliner, 50 E-46100 Burjassot, Valencia, Spain ` ` Received 25 October 1999 Abstract Ž . The complexation energies of H BPH F n s0–3 and the proton affinities of PH F compounds have been 3 3yn n 3yn n Ž . Ž . investigated at the G2 MP2 level of theory. G2 MP2 results show that the successive fluorine substitution on the phosphine increases the stability of H BPH F complexes although the basicity of the PH F ligands reduces with this 3 3yn n 3yn n substitution. The NBO partitioning scheme shows that this stability was related to the hyperconjugation effect. It proves also that the shortening of the P–H and P–F bond lengths, upon complexation, is due to an increasing ‘s’ character in these bonds. q 2000 Elsevier Science B.V. All rights reserved. 1. Introduction Compounds containing boron, nitrogen, and phos- phorus play an important role in synthetic chemistry and have received extensive attention in the chemical w x literature 1,2 . Accurate knowledge of the thermody- namics of complexation energies would serve as a useful framework from which to build a detailed and quantitative understanding of borane reactivity and mechanism. Numerous studies have been devoted to this type of compounds concerning their structural parameters, the nature of the bonding, their stability and other w x physical and chemical properties 3–14 where the analysis methods differ. Recently, Durig and Shen ) Corresponding author: Fax q 212-4-43-74-08; e-mail: boutalib@ucam.ac.ma have published a theoretical study at the MP2 level of theory of the H BPH , H BPHF , and H BPF 3 3 3 2 3 3 wx complexes using several different basis sets 5 . They have shown that the substitution of the hydrogen atoms on the phosphine group by fluorine atoms increases the stability of the corresponding com- plexes. They have also obtained that the difluo- rophosphine–borane complex is more stable than the trifluorophosphine–borane one. Skancke and wx Skancke 4 , using DFT methods, have reported that the increasing fluorine substitution on nitrogen re- duces the stability of H BNH , H BNH F, 3 3 3 2 H BNHF , and H BNF complexes. From these 3 2 3 3 Ž. results one can wonder: a why the stability de- creases upon fluorination on ammonia, while upon successive fluorine substitution on phosphine this Ž. stability increases, and b why the order of stability at the phosphorus complexes is broken with the degree of the substitution? 0009-2614r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0009-2614 00 00586-8