NONADDITIVITY OF INTERACTION IN HYDRATED CU+ AND CU-2+ CLUSTERS

Two- and three-body interaction energies are calculated by using ab initio molecular orbital theory for tetrahedral, octahedral, and cubic arrangements of H2O molecules around Cu+ and Cu2+ ions in [Cu(OH2)n]q+ clusters to assess the nonadditivity of interactions in hydrated transition-metal-ion clusters. The results are compared to full many-body results for the clusters. For Cu2+ there appears to be a slow convergence of the interaction terms to the full many-body result. For Cu+ many-body effects are much less important, although a surprising result is the finding that the second water molecule is bound more strongly to Cu+ than the first water molecule in a [Cu(OH2)2]+ cluster when the O-Cu-O angle is 180°. More detailed investigation of [Cu(OH2)]+ and [Cu(OH2)2]+ clusters confirmed this result and also revealed that the n = 2 cluster is characterized by a shorter CuO distance than the n = 1 cluster. Neither the increase in binding nor contraction of the CuO distance occurs in [Cu(OH2)n]2+ clusters in going from n = 1 to n = 2 or in clusters containing non-transition-metal monocations such as Li+ or Na+. © 1990 American Chemical Society.