Electronic structure and rotational barrier of diphosphine

Abstract

Ab initio LCAO-MO-SCF calculations have been carried out for the gauche, semi-eclipsed, staggered, and eclipsed rotamers of diphosphine, P₂H₄, using three different Gaussian basis sets. Comparison of the results obtained from these basis sets shows that allowing d character to the phosphorus atoms serves primarily only to polarize the s and p orbitals, with essentially no P—P delta bonding and no significant accentuation of P—P π bonding. The rotational energy barriers obtained from the ab initio results are compared with CNDO barriers and a simple interpretation is presented in terms of hydrogen/hydrogen, hydrogen/lone pair, and lone pair/lone pair repulsions. The orbitals of the various rotamers are correlated by means of their energies and their electron densities; an observed twisting of certain orbital electron clouds in the P—P bonding region upon internal rotation was attributed to the conservation of the delocalized nature of these orbitals.