G1 and G2 methodologies have been used to characterize P(+)L(N) (n = 1, 2 and L = NH3, OH2, FH, PH3, SH2, ClH) ion-molecule complexes in both singlet and triplet states. A topological analysis of their electron density and its associated Laplacian has been carried out in order to characterize the nature of the ion-ligand bond. Both triplet and singlet pf behave as a soft acid, for which electronic effects are dominant in the bonding. In general, the results are in close agreement with the hard-soft acid-base principle (HSAB). Thus, P+ prefers to be bonded to the softest bases. For two-ligand complexes, lower binding energies and greater energy differences between triplet and singlet states are observed. For the singlets, although there exists a decrease in the covalency of the bond, electronic effects still have considerable importance, whereas for the triplets, a greater dominance of electrostatics in the bonding is predicted along with a concomitant larger lowering of binding energies.