Structure electronique des complexes acide-base de Lewis. I. Structure electronique et conformation moléculaire des molécules F3P·BH3 et F2HP·BH3

The electronic structure and preferred conformations of F₃P·BH₃ and F₂HP·BH₃ are investigated in the framework of the CNDO /2 approximation. In complete agreement with microwave data, the staggered conformations are predicted to be the most stable ones. The barriers to internal rotation are in good agreement with experimental values (F₃P·BH₃: calc. = 3.03 kcal/mole, exp. = 3.24 ± 0.15 kcal/mole; F₂HP·BH₃: calc. = 3.63 kcal/mole, exp. = 4.05 ± 0.45 kcal/mole) and a bicentric energy partitioning shows that the variations of the total energy are completely reflected by the only variation of the interaction energy between phosphorus and H atoms bonded to boron. The analysis of the electron densities reveals the importance of the 3s(P) → 2p_x(B) transfer in the formation of the co-ordination. Finally, the computed dipole moment value and direction agree with corresponding experimental data.