The effects of 10 paramagnetic metal complexes (Fe(III)EDTA(H2O)-, Fe(III)EDTA(OH)(2-), Fe(III)PDTA(-), Fe(III)DTPA(2-), (Fe2O)-O-III(TTHA)(2-), Fe-III(CN)(6)(3-), Mn(II)EDTA(H2O)(2-), Mn(II)PDTA(2-), Mn-II beta-EDDADP(2-), and (MnPO4-)-P-II) on F- ion F-19 NMR transverse relaxation rates (R-2 = 1/T-2) were studied in aqueous solutions as a function of temperature. Consistent with efficient relaxation requiring formation of a metal/F- bond, only the substitution inert complexes Fe-III(CN)(6)(3-) and Fe(III)EDTA(OH)(2-) had no measured effect on T-2 relaxation of the F- F-19 resonance. For the remaining eight complexes, kinetic parameters (apparent second-order rate constants and activation enthalpies) for metal/F-association were determined from the dependence of the observed relaxation enhancements on complex concentration and temperature. Apparent metal/F- association rate constants for these complexes (k(app),(F)-) spanned 5 orders of magnitude. In addition, we measured the rates at which O-2(center dot-) reacts with Fe(III)PDTA(-), Mn(II)EDTA(H2O)(2-), Mn(II)PDTA(2-), and Mn-II beta-EDDADP(2-) by pulse radiolysis. Although no intermediate is observed during the reduction of Fe(III)PDTAby O-2(center dot-), each of the Mn-II complexes reacts with formation of a transient intermediate presumed to form via ligand exchange. These reactivity patterns are consistent with literature precedents for similar complexes. With these data, both k(app,O2)- and k(app,F)- are available for each of the eight reactive complexes. A plot of log(k(app,O2)-) versus log(k(app,F)-) for these eight showed a linear correlation with a slope approximate to 1. This correlation suggests that rapid metal/O-2(center dot-) reactions of these complexes occur via an inner-sphere mechanism whereas formation of an intermediate coordination complex limits the overall rate. This hypothesis is also supported by the very low rates at which the substitution inert complexes (Fe-III(CN)(6)(3-) and FeFe(III)EDTAEDTA(OH)(2-)) are reduced by O-2(center dot-). These results suggest that F- F-19 NMR relaxation can be used to predict the reactivities of other Fe-III complexes toward reduction by O-2(center dot-), a key step in the biological production of reactive oxygen species.