34 GHz e.p.r. study of vanadyl complexes in various asphaltenes: Statistical correlative model of the coordinating ligands |
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Authors: | Vivek M Malhotra Harvey A Buckmaster |
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Affiliation: | Department of Physics, The University of Calgary, Calgary, Alberta, Canada T2N 1N4 |
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Abstract: | High precision 34 GHz e.p.r. measurements were performed to study the coordination of vanadyl complexes in various asphaltenes. The spin-Hamiltonian parameter analysis indicates that the asphaltenes can be classified into those which have g- and A-parameters nearly identical to those for the vanadyl tetraphenyl porphyrins doped in carbonaceous materials and those for which these parameters are nearly identical to those for the vanadyl etioporphyrins. Quantitative statistical analysis of the parameters for model compounds with coordination N4, N2S2, NS3, S4, S2O2, N2O2 and O4 shows that these parameters cannot be used to predict the coordination for various asphaltenes. It is found that g0 is a better parameter than A0 to predict the coordination, although it cannot resolve the N4, S4 and S2O2 coordinations. However, the spin-Hamiltonian parameter resolution was sufficient to distinguish between those vanadyl complexes present in porphyrins, humates and minerals. The importance of high precision e.p.r. measurement at 34 GHz or higher frequencies for model compounds and chromatographically-separated fractions is discussed. |
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Keywords: | asphaltenes vanadyl complexes e p r |
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