An extension of the CNDO/2 formalism, similar to the method of Clack, Hush and Yandle but with a different parametrisation, is proposed for investigating the electronic structure of transition metal complexes. The results for Ni(CO)4 and Ni(PF3)4 agree well with those ofab initio calculations and with some experimental data. Such a semi-empirical approach may be performed, usingab initio results as reference data, in order to interpret the physical and chemical behaviour of largeseries of complexes in their ground state.

Une extension de la méthode CNDO/2 á l'étude des complexes d'éléments de transition

Approximately two-thirds of the chapters in these two companion volumes are devoted to methods of obtaining high-accuracy electronic wave functions for molecules and solids. The remaining third are concerned with particular chemical species or properties, and our chapter fits the latter category. Within this category the extensive literature on barriers offers two special opportunities of general interest to chemical theorists. First, it is possible to make rather definitive statements on the quality of wave functions required to yield quantitative predictions. Second, methods for analyzing ab initio wave functions to ascertain the physical origin of the barrier and provide a quantum mechanically well-defined, but simple picture of the mechanism have been more extensively developed for this topic than any other.

Barriers to Rotation and Inversion

Electron diffraction study and CNDO/2 calculations on the complex of aluminium trichloride with ammonia, Cl3Al.NH3

On the conformational analysis of (CH3)3M (M = N, P, CH, SiH) molecules: CNDO/2 calculations versus experimental data. LEM or calder conformation?

Conformational analysis in inorganic chemistry: Semi-empirical quantum calculation vs. experiment

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) → 2px(B) transfer in the formation of the co-ordination. Finally, the computed dipole moment value and direction agree with corresponding experimental data.

J.-F. Labarre

Papers

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