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The electronic structures of PH3, P(CH3)3, and PF3 have been examined with the aid of self-consistent multipolar Xa calculations (SCM-Xa-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 -symmetry p-d hybrid that comprises the lowest empty orbital in the -acceptor PF3 ligand.Trivalent phosphorus donor ligands, PZ3 (Z = F, Cl, H, alkyl, aryl, O-alkyl, O-aryl), have played an important role in the development of coordination and organometallic chemistry. They form tractable complexes with nearly all the transition elements, and PZ3 ligands are compatible with most metal oxidation states and ancillary ligands. The electron-pair donor properties of phosphine ligands appear to follow sensible patterns. For example, trialkylphosphines generally form stronger metal-ligand bonds than triarylphosphines, when ligand basicity effects predominate.1Of course, steric factors2 may be important in congested complexes. Ligand basicity trends fail to explain3 10the unusual stability of complexes that contain phosphite and PX3 (X = F, Cl) ligands.

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