ESR Studies and the Electronic Structure of Vanadyl Ion Complexes

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 b_2g^* orbital. The extrahyperfine splitting is very isotropic which indicates that the b_2g^* 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 b_2g^* 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.