Two aspects of the aqueous chemistry of [V(H2O)(6)](2+/3+) have been studied at the B3LYP level of theory. The first one concerns the role of an explicit second coordination sphere of 12 water molecules on the structures of hexahydrated V(II) and V(III) ions. For the two cations, the most stable conformers correspond to a wheel-like structure in which the second hydration shell can be viewed as being constituted of three open quadrimers, each one being connected by one hydrogen bond to the other two and to three ligands of the first sphere through four additional hydrogen bonds. The [V(H2O)(6)](3+) subunit in this conformer is found to mimic the arrangement observed in [V(H2O)(6)][H5O2](CF3SO3)(4) (Cotton, F. A; Fair, C. K.; Lewis, G. E.; Mott, G. N.; Ross, F. K.; Schultz, A. J.; Williams, J. M. J. Am. Chem. Soc. 1984, 106, 5319). The others conformers investigated, for which the second hydration shell consist of four noninteracting cyclic trimers, were calculated to be 15.6 kcal/mol (V3+) and 13.6 kcal/mol (V2+) higher in energy at the in vacuo level. These differences were increased to 22.8 kcal/mol (V3+) and 18.5 kcal/mol (V2+) when taking into account the bulk solvent using a polarizable continuum model. For the water-exchange mechanisms, we find that, for both cations, the D mechanism is the preferred one at the gas-phase level using density functional theory calculations. The effect of the solvent on the activation barriers (DeltaE(double dagger)) is emphasized because it induces inversions in the A-/ D- and I-/D- reaction-path orderings. On the basis of the calculated DeltaE(double dagger) values in solution, the water-exchange mechanism is expected to proceed via a limiting A pathway and an I-activation process for V3+ and V2+, respectively. The differences between the experimental DeltaH(double dagger) values and the computed activation barriers were found to be 0.6 kcal/mol and -2.6 kcal/mol, respectively. The effect of the hydration energy on the stability and, hence, the lifetime of the various intermediates is also discussed.