The reaction of [PPN][Fe(CO)(3)(NO)] and S-8 in a 1:1 molar ratio in THF proceeded to give the dinitrosyl iron complex [PPN][S5Fe(NO)(2)] (1) and the known [PPN](2)[S5Fe(mu-S)(2)FeS5] (2). EPR signals of g values g(z) = 2.0148, g(x) = 2.0270, and g(y) = 2.0485 at 77 K confirmed the existence of the unpaired electron in compound 1. The temperature-dependent magnetic moment of complex 1 indicates that the ground state is one unpaired electron with (S-t, S-L) = (1/2, 1) at very low temperature (S-t is the total spin quantum number of the system; S-L is the sum of the spin quantum numbers of two NO ligands). The O K-edge absorptions of complex 1 and [(NO)Fe(S2CNEt2)(2)] at 532.1 and 532.5 eV are assigned to the transition of 1s --> pi*(NO) and 1s -pi*(NO+), respectively. For the electronic structure of the {Fe(NO)(2)} core, DFT calculations, magnetic susceptibility measurement, EPR, and Fe K-/L-edge XAS spectroscopy of complex 1 lead to a description of {Fe1+((NO)-N-.)(2)}(9). [2Fe-2S] cluster 2 treated with nitric oxide in THF shows that cluster 2 is transformed into the dinitrosyl iron complex 1 identified by IR, UV-vis, and X-ray diffraction analysis. The reaction may be reversed by the photolysis of the THF solution of 1 in the presence of the NO-accepting reagent [(C4H8O)Fe(S,S-C6H4)(2)](-) to reform 2. This result demonstrates a successful biomimetic reaction cycle of the degradation and reassembly of [2Fe-2S] cluster [S5Fe(mu-S)(2)FeS5](2-) relevant to the repair of nitric oxide-modified [2Fe-2S] ferredoxin by cysteine desulfurase and L-cysteine in vitro.