title: Discrimination of mononuclear and dinuclear dinitrosyl iron complexes (DNICs) by S K-edge X-ray absorption spectroscopy: insight into the electronic structure and reactivity of DNICs.
abstract: In addition to probing the formation of dinitrosyl iron complexes (DNICs) by the characteristic Fe K-edge pre-edge absorption energy ranging from 7113.4 to 7113.8 eV, the distinct S K-edge pre-edge absorption energy and pattern can serve as an efficient tool to unambiguously characterize and discriminate mononuclear DNICs and dinuclear DNICs containing bridged-thiolate and bridged-sulfide ligands. The higher Fe-S bond covalency modulated by the stronger electron-donating thiolates promotes the Fe → NO π-electron back-donation to strengthen the Fe-NO bond and weaken the NO-release ability of the mononuclear DNICs, which is supported by the Raman ν(Fe-NO) stretching frequency. The Fe-S bond covalency of DNICs further rationalizes the binding preference of the {Fe(NO)(2)} motif toward thiolates following the trend of [SEt](-) > [SPh](-) > [SC(7)H(4)SN](-). The relative d-manifold energy derived from S K-edge XAS as well as the Fe K-edge pre-edge energy reveals that the electronic structure of the {Fe(NO)(2)}(9) core of the mononuclear DNICs [(NO)(2)Fe(SR)(2)](-) is best described as {Fe(III)(NO(-))(2)}(9) compared to [{Fe(III)(NO(-))(2)}(9)-{Fe(III)(NO(-))(2)}(9)] for the dinuclear DNICs [Fe(2)(μ-SEt)(μ-S)(NO)(4)](-) and [Fe(2)(μ-S)(2)(NO)(4)](2-).
authors: Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors: Tsai-Te
authors: TT
authors: Lu
authors: Szu-Hsueh
authors: SH
authors: Lai
authors: Ya-Wen
authors: YW
authors: Li
authors: I-Jui
authors: IJ
authors: Hsu
authors: Ling-Yun
authors: LY
authors: Jang
authors: Jyh-Fu
authors: JF
authors: Lee
authors: I-Chia
authors: IC
authors: Chen
authors: Wen-Feng
authors: WF
authors: Liaw