High Pressure 17O‐FT‐NMR. Evidence for the Associative Nature of Substitution Reactions on Mn2+ in Water

The water exchange on [Mn(H2O)6](ClO4)2 in aqueous solution has been studied as a function of pressure (up to 250 MPa), measuring 17O‐FT‐NMR. linewidths of the free water resonance at 8.13 MHz. A pressure independent volume of activation, ΔV≠ = −6.2 ± 0.2 cm3 mol−1 is obtained, producing a clear evidence that, contrary to general belief, the mechanism for solvent exchange on Mn2+ is an associative interchange (Ia).