Probing the molecular geometry of five-coordinate vanadyl complexes with pulsed ENDOR

The pulsed electron paramagnetic resonance (EPR) technique of V-51 electron spin echo-electron nuclear double resonance (ESE-ENDOR) has been used to m easure the nuclear quadrupole coupling constants of a series of five-coordi nate vanadyl complexes containing Schiff base ligands with geometries rangi ng from distorted square pyramidal to distorted trigonal bipyramidal. Vanad ium nuclear quadrupole coupling constants are sensitive to the coordination geometry of the vanadyl ion, and thus sensitive to the structural distorti ons within this series of complexes. V-51 ESE-ENDOR has been shown to be a probe of the coordination geometry of vanadyl complexes. Such a spectroscop ic probe should prove useful in the investigation of vanadyl of unknown coo rdination geometry, such as may be found in the interaction of the vanadyl ion with biomolecules.