ESR Studies and the Electronic Structure of Vanadyl Ion Complexes

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Abstract
The ESR spectra of vanadyl acetylacetonate and tetraphenylporphyrin have been studied in various liquid solvents and frozen glasses. The spectra have been analyzed and the components of the g tensor and of the vanadium hyperfine interaction tensors have been determined, and for the porphyrin the nitrogen extrahyperfine interaction tensor has been obtained. The unpaired electron is in the b2g* orbital. The extrahyperfine splitting is very isotropic which indicates that the b2g* orbital is localized on the vanadium in the porphyrin complex and the ``in‐plane π bonding'' is slight. An explanation of the origin of this extrahyperfine splitting is discussed in terms of configuration interaction. An analysis of the vanadium hyperfine interaction indicates that the b2g* orbital is localized on the vanadium in the acetylacetonate also, and that the Fermi contact interaction depends upon a number of excited configurations and varies from complex to complex and with change of solvent. The g‐tensor analysis suggests that the spin—orbit constant λ≥170 cm—1, that the in‐plane σ antibonding and out‐of‐plane π antibonding orbitals are delocalized, the delocalization increasing in the order: VO(H2O)5+ +, vanadyl acetylacetonate, vanadyl porphyrin.

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