Single-crystal and powder EPR studies of the S=1/2 ground state of the iron-sulfur core in [tris(tetraethylammonium)]-[tetrakis(benzylthiolato)tetrakis(mu(3)-sulfido)tetrairon]center dot(N,N-dimethylformamide) with crystal structure determination

The crystal structure at room temperature of the solvated iron-sulfur synthetic compound (Et(4)N)(3)[Fe4S4(SCH2-Ph)(4)]. DMF has been determined. The conformation of four ligand branches CH(2)Ph linked to the Fe4S8 unit is very disturbed in contrast with the much more symmetrical situation in the already known nonsolvated compound. The paramagnetic core [Fe4S4](+) has been studied by electron paramagnetic resonance (EPR) at a few kelvins in single crystals: it has an S = 1/2 ground state in contrast with the S = 3/2 ground state in the nonsolvated compound. It is the first S = 1/2 ground state studied in a single crystal for an iron-sulfur synthetic compound and has g values of 2.027, 1.930, and 1.904 and principal directions near the three normals to opposite ''faces'' of the cubane [Fe4S4](+). Polycrystalline EPR studies were done to observe alterations of the product but also are analyzed in relation with previous frozen solution studies.