HIGH-PRESSURE NMR KINETICS .6. O-17 FT NMR-STUDY OF THE EFFECT OF PRESSURE ON THE EXCHANGE OF WATER ON NICKEL(II)

The solvent exchange of [Ni(H2O)6](ClO4)2 in water has been studied as a function of temperature and pressure (up to 225 MPa) by measuring oxygen-17 FT NMR chemical shifts and line widths of the free water resonance at 8.133 MHz. A volume of activation ΔV* of+7.1±0.2 cm3 mol-1 is obtained by using the full Swift and Connick equation and is found to be independent of pressure. The activation parameters ΔH* and ΔS* are very sensitive to the method of analysis used. The three activation parameters are in accord with a dissociative-interchange (Id) mechanism. The temperature and pressure dependences of pure acidified water T2's have also been studied by oxygen-17 FT NMR. The relaxation rate decreases with compression, suggesting that the effect of pressure is to destroy some of the water structure. © 1979, American Chemical Society. All rights reserved.