A combination of N/S/Fe K-edge X-ray absorption spectroscopy (XAS), X-ray diffraction data, and density functional theory (DFT) calculations provides an efficient way to unambiguously delineate the electronic structures and bonding characters of Fe-S, N-O, and Fe-N bonds among the direduced-form Roussin's red ester (RRE) [Fe-2(mu-SPh)(2)(NO)(4)](2-)(1) with {Fe(NO)(2)}(10)-{Fe(NO)(2)}(10) core, the reduced-form RRE [Fe2(mu-SPh)(2)(NO)(4)](-)(3) with {Fe(NO)(2)}(9)-{Fe(NO)(2)}(10) core, and RRE [Fe-2(mu-SPh)(2)(NO)(4)] (4) with {Fe(NO)(2)}(9)-{Fe(NO)(2)}(9) core. The major contributions of highest occupied molecular orbital (HOMO) 113 alpha/beta in complex 1 is related to the antibonding character between Fe(d) and Fe(d), Fe(d), and S atoms, and bonding character between Fe(d) and NO(pi*). The effective nuclear charge (Z(eff)) of Fe site can be increased by removing electrons from HOMO to shorten the distances of Fe center dot center dot center dot Fe and Fe-S from 1 to 3 to 4 or, in contrast, to increase the Fe-N bond lengths from 1 to 3 to 4. The higher IR nu(NO) stretching frequencies (1761, 1720 cm(-1) (4), 1680, 1665 cm(-1) (3), and 1646, 1611, 1603 cm(-1) (1)) associated with the higher transition energy of N1s ->sigma*(NO) (412.6 eV (4), 412.3 eV (3), and 412.2 eV (1)) and the higher Z(eff) of Fe derived from the transition energy of Fe-1s -> Fe-3d (7113.8 eV (4), 7113.5 eV (3), and 7113.3 eV (1)) indicate that the N-O bond distances of these complexes are in the order of 1 > 3 > 4. The N/S/Fe K-edge XAS spectra as well as DFT computations reveal the reduction of complex 4 yielding complex 3 occurs at Fe, S, and NO; in contrast, reduction mainly occurs at Fe site from complex 3 to complex 1.