SPIN CHANGE INDUCED IN VANADIUM(I) BY LOW-FIELD LIGANDS - BINDING-ENERGIES OF V(+)(H2)(N) CLUSTERS (N=1-7)

Dissociation energies for H-2 loss from V+(H-2)n clusters have been determined via temperature-dependent equilibrium measurements for clusters containing up to seven H-2 ligands (D.E. = -DELTAH-degrees0 = 10.2, 10.7, 8.8, 9.0, 4.2, 9.4, < 2.5 kcal/mol for n = 1-7, respectively). The V+(H-2)n clusters for n = 1 and 2 are less strongly bound than the corresponding Co+(H-2)n clusters, in agreement with recent theoretical results. We find an anomalously high binding energy for the sixth hydrogen ligand on vanadium and argue this is due to a change in spin state from a quintet to a triplet. The clustering entropies were also measured. Results are also presented for V+-(H2O)(H-2)n with binding energies of 9.9, 8.5, and 6.9 kcal/mol for n = 1-3, respectively, and V+(H2O)2(H-2) with a binding energy of 6.7 kcal/mol. The present results are compared with recent calculations on the V+(H-2)n systems.