HIGH-PRESSURE NUCLEAR MAGNETIC-RESONANCE KINETICS .5. PROTON NUCLEAR MAGNETIC-RESONANCE STUDY OF THE EFFECT OF PRESSURE ON THE EXCHANGE OF NON-AQUEOUS SOLVENTS ON NICKEL(II) AND COBALT(II)

The effect of pressure (up to 200 MPa) on the solvent exchange of MS6(C104)2 with M = Ni or Co and S = N, N-dimethylformamide (DMF), acetonitrile, or methanol has been studied by utilizing 1H FT NMR T2 measurements. The derived volumes of activation, ΔV (cm3 mol-1), for the above solvent series with Ni(II) are 9.1 ± 0.3 (297 K), 9.6 ± 0.3 (294 K), and 11.4 ± 0.6 (307 K) and with Co(II) are 6.7 ± 0.3 (296 K), 9.9 ± 0.7 (260 K), and 8.9 ± 0.3 (279 K). These values are in accord with a dissociative interchange mechanism, although they suggest Co(II) exhibits less dissociative character than Ni(II). For both ions, the solvent variation of ΔV*/V° mirrors that of ΔG*; these results may suggest that the faster the reaction, the less dissociative character it has. © 1979, American Chemical Society. All rights reserved.