Dinitrosyl iron complex [(-SC7H4SN)(2)Fe(NO)(2)](-) (1) was prepared by reaction Of [S5Fe(NO)(2)] and bis(2-benzothiozolyl) disulfide. In synthesis of the analogous dinitrosyl iron compounds (DNICs), the stronger electron-donating thiolates [RS](-) (R = C6H4-o-NHCOCH3, C4H3S, C6H4NH2, Ph), compared to [-SC7H4SN](-) of complex 1, trigger thiolateligand substitution to yield [(-SC6H4-o-NHCOCH3)(2)Fe(NO)(2)](-) (2), [(-SC4H3S)(2)Fe(NO)(2)](-) (3), and [(SPh)(2)Fe(NO)(2)](-) (4), respectively. At 298 K, complexes 2 and 3 exhibit a well-resolved five-line EPR signal at g = 2,038 and 2,027, respectively, the characteristic g value of DNICs. The magnetic susceptibility fit indicates that the resonance hybrid of {Fe+((NO)-N-.)(2)}(9) and {Fe-(+NO)(2)](9) in 2 is dynamic by temperature. The IR v(NO) stretching frequencies (ranging from (1766, 1716) to (1737, 1693) cm(-1) (THF)) of complexes 1-4 signal the entire window of possible electronic configurations for such stable and isolable {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)](-). The NO-releasing ability of {Fe(NO)(2))(9) [(RS)(2)Fe(NO)(2)](-) is finely tuned by the coordinated thiolate ligands. The less electron-donating thiolate ligands coordinated to {Fe(NO)(2)}(9) motif act as better NO-donor DNICs in the presence of NO-trapping agent [Fe(SSC6H4)(2)](2)(2-). Interconversion between {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)](-) and {Fe(NO)(2)](10) [(Ph3P)(2)Fe(NO)(2)] was verified in the reaction of (a) [(RS)(2)Fe(NO)(2)](-), 10 equiv of PPh3 and sodium-biphenyl, and (b) 2 equiv of thiol, [RS](-), and [(Ph3P)(2)Fe(NO)(2)], respectively. The biomimetic reaction cycle, transformation between {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)] and {Fe(NO)(2)](9) [(R'S)(2)Fe(NO)(2)](-), reversible interconversion of {Fe(NO)(2)](9) and {Fe(NO)(2)}(10) DNICs, and degradation/ reassembly of [2Fe-2S] clusters may decipher and predict the biological cycle of interconversion of I Fe(NO)219 DNICs, {Fe(NO)(2)}(10) DNICs, and the [Fe-S] clusters in proteins.