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Characterization of (P+Lx)Ly Ion Molecule Clusters of First-Row Hydrides

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posted on 20.03.1996, 00:00 by Xabier Lopez, Jesus M. Ugalde, Fernando P. Cossío
Ab initio calculations of phosphorus ionic clusters of the type PL+·L, PL2+·L, PL3+, and PL4+, with L = NH3, OH2, and FH, in both triplet and singlet states have been carried out, in order to determine their geometries and binding energies. The nature of the binding has also been extensively studied by means of both the topological analysis of the total electron charge density and the natural bond orbital analysis. When the ligand is bound as a second ligation shell through a formal hydrogen bond, significant cooperative effects between the two ligand shells have been detected. Substantial covalency is found for these hydrogen bonds, along with the weakening of the hydride bond with the inner ligand and the reinforcing of the bond between the inner ligand and the phosphorus. These processes are greatly favored for the singlet state of the phosphorus, and for the case of ammonia and water ligands, conversion reactions leading to PXHn-1·XHn+1+ complexes are observed. It has been found that the maximum number of ligands bound to (3P)P+ is two, whereas that maximum is ligand dependent in the case of (1D)P+, with two for NH3, three for OH2, and four for FH. We have also observed that soft ligands present a sharp decrease in successive binding energies to phosphorus, whereas hard ligands show smoother variations. Finally, for most cases, the addition of the new ligand as a second ligation shell is favored with respect to the direct addition to the phosphorus, since cooperative effects make more efficient the donation of electronic charge to the phosphorus ion.