EPR Linewidth Study of Vanadyl Complexes in Various Solvents

Publisher Website
Google Scholar
Abstract
The temperature dependences of the EPR linewidths for vanadyl acetylacetonate, VO(acac)2, have been measured in ethanol, n-propanol, isopropanol, n-butanol, t-butanol, trifluoroethanol, and trichloroethanol. A similar study has been carried out on vandayl trifluoroacetylacetonate, VO(tfac)2, in methanol and the solvated vanadyl ion, VO2+, in water. The EPR linewidths have been measured at 25°C for VO2+ in dimethyl sulfoxide, trimethyl phosphate, acetonitrile, N ,N-dimethylformamide, and methanol. The results are interpreted in terms of the theory proposed by Kivelson et al. to obtain rotational correlation times (τR) for the various systems. The results generally conform to the predictions of the modified Debye theory, in that τR and solvent visocity show the expected temperature dependence. Only VO(tfac)2 in methanol appears to be anomalous in this respect. A detailed analysis has shown that one of the parameters (γ) in Kivelson's expression for the linewidths is less sensitive to experimental error and therefore best suited for calculations of τR. The results indicate that at low temperature some mechanism in addition to spin–rotational relaxation is contributing to the “residual” linewidth.