Light triggers the formation of HNO from a metal− nitrosyl species, facilitated by an intramolecular pendant thiol proton. Two {FeNO} 6 complexes (the Enemark−Felthan notation), [Fe(NO)( TMS PS2)( TMS PS2H)] (1, TMS PS2H 2 = 2,2′dimercapto-3,3′-bis(trimethylsilyl)diphenyl)phenylphosphine; H is a dissociable proton) with a pendant thiol and [Fe(NO)-( TMS PS2)( TMS PS2CH 3 )] (2) bearing a pendant thioether, are spectroscopically and structurally characterized. Both complexes are highly sensitive to visible light. Upon photolysis, complex 2 undergoes NO dissociation to yield a mononuclear Fe(III) complex, [Fe( TMS PS2)( TMS PS2CH 3 )] (3). In contrast, the pendant SH of 1 can act as a trap for the departing NO radical upon irradiation, resulting in the formation of an intermediate A with an intramolecular [SH•••ON−Fe] interaction. As suggested by computational results (density functional theory), the NO stretching frequency (ν NO ) is sensitive to the intramolecular interaction between the pendant ligand and the iron-bound NO, and a shift of ν NO from 1833 (1) to 1823 cm −1 (A) is observed experimentally. Subsequent photolysis of the intermediate A results in HNO production and a thiyl group that then coordinates to the Fe center for the formation of [Fe( TMS PS2) 2 ] (4). In contrast with the common acid−base coupling pathway, the HNO is not voluntarily yielded from 1 but rather is generated by the photopromoted pathway. The photogenerated HNO can further react with [Mn III ( TMS PS3)(DABCO)] ( TMS PS3H 3 = (2,2′2′′-trimercapto-3,3′,3′′tris(trimethylsilyl)triphenylphosphine; DABCO = 1,4-diazabicyclo[2.2.2]octane) in organic media to yield anionic [Mn(NO)-( TMS PS3)] − (5 − ) with a {MnNO} 6 electronic configuration, whereas [Mn III ( TMS PS3)(DABCO)] reacts with NO gas for the formation of a {MnNO} 5 species, [Mn(NO)( TMS PS3)] (6). Effective differentiation of the formation of HNO from complex 1 with the pendant SH versus NO from 2 with the pendant SMe is achieved by the employment of [Mn III ( TMS PS3)(DABCO)].

A dimeric dithiolate-bridged species, [Fe­(NO)­(PS2)]2 (1) containing two {FeNO}7 units, can be isolated by treating [Fe­(CO)2(NO)2] with PS2H2 (PS2H2 = bis­(2-dimercaptophenyl)­phenylphosphine). Crystallographic studies reveal the syn-configuration of NO units and the bridging thiolates in the butterfly shape of the 2Fe2S core. Addition of PPh3 to the solution of dinuclear 1 leads to the formation of mononuclear {FeNO}7 [Fe­(NO)­(PS2)­(PPh3)] (2) that shows electrochemical responses similar to those of 1. One-electron reduction of 1 with Cp*2Co or KC8 results in the isolation of thiolate-bridged bimetallic DNIC, [(PS2)­Fe­(μ-PS2)­Fe­(NO)2]− ([3]−), confirmed by several spectroscopies including single-crystal X-ray diffraction studies. The bimetallic DNIC [3]− is a rare example obtained from the one-electron reduction of a dinuclear Fe-NO {FeNO}7 model complex. With the assistance of redox behaviors of 2, electrochemical studies imply that the reduction of 1 leads to the formation of a mononuclear {FeNO}8 [Fe­(NO)­(PS2)­(THF)]− intermediate, which involves disproportionation or NO– transfer to yield [3]−. Based on IR data and magnetic properties, the electronic structure of [3]− can be described as a FeII/{Fe­(NO)2}9 state. Isolation of the {Fe­(NO)2}9 moiety coordinated by the Fe ancillary complex lends strong support to the NO scrambling behavior in the effectiveness of the activity of flavodiiron nitric oxide reductases (FNORs).