The X-band, 9.473 GHz, electron paramagnetic resonance (EPR) spectrum for [Co(D4)(dca)] at 12 K is much like the EPR spectrum for Co-bovine serum albumin (CoBSA) in that the g-values are similar and no cobalt hyperfine lines are resolved. The L-band, 1.37 GHz, EPR spectrum for [Co(D4)(dca)] is resolved into at least four broad lines about g=4. Determining whether broad lines are hill-shaped for geff-max or S-shaped for geff-mid is difficult; therefore, we obtained the second harmonic spectrum, which is better for resolution of sharp lines. Initial EPR parameters from the experimental spectrum are geff-mid about 4, A-mid=66 G (initial value for A-mid taken from the two well-resolved low-field lines). Starting with the EPR parameters from the spectrum as determined above, a simulation using EasySpin gives the following parameters, which are consistent with but not necessarily unique: A=[300, 400, 150 MHz] equal to A=[48, 50, 54 G] and g=[6.0, 4.3, 2.0]. A-mid dominates the spectrum for [Co(D4)(dca)] (see figure, top panel, where the line width is broadened for lines around g-max and g-min in the simulation, thus emphasizing lines about g-mid).

Better resolution of hyperfine lines for high-spin cobalt at low frequency, L-band: [Co(D4)(dca)]

2019 Fall National Meeting

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