Complexes [(NO)(2)Fe(S-(BU)-B-t)(2)](-) (3-Na) and [Fe-2((SBu)-S-/right angle-Bu-t)(2)(NO)(4)] (1) are in dynamic equilibrium in the protic solvent MeOH. The subsequent addition of the equivalent of cobaltocene into the MeOH solution mixture of complexes 3-Na and 1 led to the formation of the fully delocalized mixed-valence [Fe((/right angle)-LS-Bu-t)(NO)(2)](2)- (2) characterized by IR, UV-vis, EPR, SQUID, and single-crystal X-ray diffraction. The EPR spectrum of complex 2 displaying an axial signal at g perpendicular to = 2.009, g parallel to = 1.965 (77 K) and an isotropic signal at g = 1.998 (298 K), identical to the EPR spectra of reduction of dinitrosyl iron complex (DNIC)/aconitase obtained from nitrosylation of aconitase and reduction of HiPIP-containing protein-bound DNIC, suggests that the [4Fe-4S](2+) clusters of aconitase/HiPIP were nitrosylated to produce a mixture of the monomeric and dimeric DNICs.