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|Title:||An unusual temperature dependence of the EPR parameters of copper(II) and oxovanadium(IV) bis(acetylacetonate) complexes||Authors:||HOWES B., D
|Keywords:||electron paramagnetic resonance; acetylacetonate complexes; hyperfine coupling||Issue Date:||1999||Project:||None||Journal:||MAGNETIC RESONANCE IN CHEMISTRY||Abstract:||
A series of X-band electron paramagnetic resonance (EPR) spectra were obtained in the temperaturerange 120–280K at 10K intervals for the bis(acetylacetonate) complexes of copper(II) and oxovanadium(IV) cationsin dimethylformamide. The magnetic parameters and molecular rotational correlation time determined from simulationsof the spectra revealed an unexpected temperature dependence of the isotropic hyperfine coupling constant .Aiso/. Asmall, but non-negligible, abrupt increase in Aiso is observed for both complexes at a temperature (215 K) correspondingto the change in molecular motional state from the rigid limit to slow motion. The change is approximately the same forboth the Cu(II) and vanadyl complexes (ca 2 104 cm1/. No temperature dependence is observed in the isotropicg-factor for either complex within the experimental error. It is proposed that the data can be explained in termsof a change in the degree of distortion at the metal site coincident with the change in motional state and inducedby a solvent (dimethylformamide) phase transition. Calculation of the bonding parameters shows that the in-plane-bonding is more covalent in the vanadyl complex. Comparison with data from the literature reveals the importanceof the solvent in determining the type of temperature dependence displayed by the magnetic parameters.
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