Zero-field electron magnetic resonance spectra of copper carboxylates

Abstract

The design of a new zero-field electron magnetic resonance spectrometer including cryogenic capabilities and a new tuning mechanism for sweeping over approximately two octaves is described. The tuning mechanism is based on a one-loop, two-gap resonator mounted on quartz rods in such a manner that rotating the rods changes the width of the gap and the resonant frequency of the resonator. The spectrometer was used to measure the zero-field emr spectra of several copper carboxylate dimers at 90 K and 70 K. The parallel hyperfine structure was well resolved in all of the spectra and this allowed accurate determination of D, E, and A‖. A⊥ was found to be poorly defined in general and least square refinements attached large errors to this term in the spin Hamiltonian. The zero-field terms in the spin Hamiltonian at 90 K were determined to be D=9.828 GHz, E=83 MHz, A‖=217 MHz for [Cu(CH3CO2)2(CO(NH2)2)]2⋅2H2O; D=9.985 GHz, E=43 MHz, A‖=221 MHz for [Cu(C2H5CO2)2(H2O)]2; D=10.107 GHz, E=49 MHz, A‖=218 MHz for [Cu(C2H5CO2)2(CO(NH2)2)]2; D=9.979 GHz, E=192 MHz, A‖=223 MHz for [Cu(C6H5CO2)2(C6H5CO2H)]2. A model which assumes A⊥=0 is discussed in detail as it was found that all of the features observed in the spectra could be interpreted using simple explicit expressions derived from the model.