Nature of the Frontier Orbitals in Phosphine, Trimethylphosphine, and Trifluorophosphine

The electronic structures of PH3, P(CH3)3, and PF3 have been examined with the aid of self-consistent multipolar Xα calculations (SCM-Xα-DV). There is excellent agreement between the theoretical and experimental ionization energies. When the transition-state procedure is used, first ionization potentials of 10.39, 8.41, and 12.19 eV are calculated for PH3, P(CH3)3, and PF3, respectively. Experimental values are 10.58, 8.58, and 12.27 eV, respectively. Plots of the highest and lowest unoccupied orbitals provide insight into the role of phosphorus donor ligands in transition-metal systems. Especially interesting is the Tr-symmetry p-d hybrid that comprises the lowest empty orbital in the 7r-acceptor PF3 ligand.