THEORETICAL-STUDIES OF DIPHOSPHENE AND DIPHOSPHINYLIDENE .2. SOME UNUSUAL FEATURES OF THE RADICAL CATIONS AND ANIONS

Various states of HPPH+ and H2PP+ cations have been studied by using ab initio molecular electronic structure theory. These include the 2Ag, 2Au, and 2Bu states of trans-HPPH+, the 2B1 and 2A1 states of cis-HPPH+, and the 2B2 and 2B1 states of planar H2PP+. The cationic state of lowest energy is the planar H2PP+ 2B2 state. For trans-HPPH+ the SCF results are misleading; they indicate that a skewed HPPH+ 2A state lies below the trans states. However, optimization at the CISD level of theory shows that the trans-HPPH+ 2Ag state is the most stable HPPH+ cationic state. Four anionic states were studied by using an extended basis set with diffuse functions: trans-HPPH- 2Bg, cis-HPPH- 2A2, planar H2PP- 2B2, and pyramidal H2PP- 2A′. The first of these has the lowest energy, but planar H2PP has the highest electron affinity (to form the pyramidal anion). Finally, bond orders in the various states are analyzed. © 1990 American Chemical Society.