Synthesis, crystal structures, Mossbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

The iron-sulfur nitrosyl complexes A[Fe4S3(NO)(7)] where A = Na+, NH4+, or N(Bu-n)(4)(+) and B-2[Fe2S2(NO)(4)], where B = Na+, Cs+, or N(Bu-n)(4)(+), were synthesized. Their structures and properties were studied by X-ray dif fraction analysis, Mossbauer; spectroscopy, and cyclic voltammetry. The eff ect of the crystal packing on the geometry of the tetranuclear NH4[Fe4S3(NO )(7)]. H2O and binuclear Cs-2[Fe2S2(NO)(4)]. 2H(2)O complexes was analyzed. The changes in the Fe-57 Mossbauer spectral parameters of the anion in the Bz[Fe2S2(NO)(4)] series depend on the size of the B cation and agree with variations in the structural parameters of the Fe[S-2(NO)(2)] chromophores as well as in the stretching vibrations of the NO groups caused by changes in intermolecular contacts. The presence of electronic states delocalized t hrough the Fe-Fe bonds explains the fact that the electronic states of the Fe-a(S3NO) and Fe-b(S-2(NO)(2)) chromophores in the [Fe4S3(NO)(7)](-) anion are nearly identical. The binuclear clusters are unstable upon storage in the solid phase and decompose in solutions to form the tetranuclear [Fe4S3( NO)(7)](-) complexes, sulfur, and nitrogen oxides. The redox properties of the [Fe4S3(NO)(7)](-) and [Fe2S2(NO4)](2-) anions in CH3CN and THF solution s were studied. The mechanism of reduction of the anion in the tetranuclear cluster is proposed.