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An ENDOR study has been made of oxovanadium(IV) tetraphenylporphyrin randomly oriented in rigid solution.The ENDOR spectra give information on the 14N hyperfine and quadrupole tensor components as well as the hyperfine tensor components of the pyrrole protons. A comparison of the 14N data obtained here with those previously reported for silver and copper tetraphenylporphyrin clearly establishes the difference in orbital ground state of the d1 2and d9 systems. Using chloroform-toluene as a solvent matrix, we could measure all three hyperfine tensor components of the pyrrole protons. As expected for a system in which the unpaired electron is confined almost completely to the 3d^a tomic orbital of the metal ion, the pyrrole proton hyperfine tensor is axial with values of 1.38, -0.26, and -0.26 MHz. Assuming that the traceless component of the proton hyperfine is due to point dipole-dipole interaction between the unpaired electron at the vanadium nucleus and the proton spin, one calculates that the distance between the two spins is 5.24 A. This value is in good agreement with crystallographic data. Adduct-forming solvents, such as pyridine, have little effect on the 14N parameters but affect the proton ENDOR strongly.

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