The technique of V-51 electron spin echo-electron nuclear double resonance (ESE-ENDOR) has been used to investigate a structurally diverse series of oxovanadium(IV) complexes. From ENDOR spectra, V-51 nuclear quadrupole coupling constants, which reflect the electric field gradient established at the vanadium nucleus, are estimated using a perturbation theory approach. The magnitude of the nuclear quadrupole interaction is reduced by ligands binding trans to the oxygen of the oxovandium moiety due to a reduction of the electric field gradient that is established primarily by the oxo bond. Variation of ligands containing nitrogen and oxygen donor atoms oriented cia to the oxo bond gives rise to minimal changes in the quadrupole coupling constant. The nuclear quadrupole coupling constant is thus shown to be sensitive to ligands binding trans to the oxygen of the oxo bond. ENDOR can thusly serve as a new spectroscopic probe in the identification of weakly coordinating donors in the axial position such as may be found in vanadyl-substituted proteins.