NMR AND EPR LINE-BROADENING EFFECTS OF VANADYL ION IN N,N-DIMETHYLFORMAMIDE

The temperature dependence of the NMR linewidths of the formyl proton in solutions of VO2+ in N,N-dimethylformamide (DMF) indicates that proton relaxation is controlled by outer-sphere dipole-dipole interactions, chemical exchange, and inner-sphere dipole-dipole interactions, in the temperature ranges -55°-+6°, +7°-107°, and 108°-150°, respectively. At 25°C the rate constant for chemical exchange is (2.3/n)×103 sec-1, ΔH† = 7.25 kcal/mole, and ΔS†= (-18.2-4.58 logn) eu, where n is the number of exchanging DMF molecules. The linewidths of the EPR spectrum of VO2+ in DMF solutions have been interpreted in terms of the theory developed by Kivelson. The rotational correlation time, τc= 1.2×10-10 sec, calculated from this theory is shown to be consistent with the observed EPR linewidths and adequately explains the dipole-dipole line broadening observed in the NMR spectra.