EPR STUDY OF THE [FE4S4](+) STATE IN SINGLE-CRYSTALS OF (ET(4)N)(3)[FE4S4(SCH(2)PH)(4)] - G-TENSORS OF KRAMERS DOUBLETS OF THE S=3/2 GROUND-STATE

Electron paramagnetic resonance (EPR) of single crystals of the synthetic compound (Et(4)N)(3)[Fe4S4(SCH2-Ph)(4)] is presented. The measurements had to be done at very low temperature (a few kelvins) to avoid broadening of the EPR lines by the fast spin-lattice relaxation. Broadening and splittings of the lines result nevertheless from the spin-spin interactions between the paramagnetic [Fe4S4](+) ''cubanes''. However, one can follow the EPR lines of the transitions within the fundamental and excited Kramers doublets associated with the effective spin S = 3/2 of the ion [Fe4S4](+). The two corresponding effective g-tensors are associated with a strongly nonaxial zero field splitting tenser (lambda congruent to 1/3) and real g values around g(av) = 1.9. These results are discussed in relation to the theories of strong double exchange.