Abstract
The formation of hydrosulfide-bound {Fe(NO)2}9 dinitrosyl iron complex (DNIC), [K-18-crown-6-ether][(HS)2Fe(NO)2] (1) ([PPN][(HS)2Fe(NO)2] (1-PPN)) and the precursor mononitrosyl iron complex (MNIC), [PPN][(HS)3Fe(NO)] (3), were synthesized and characterized. Transformation of complex 1 into Roussin’s red salt (RRS) along with release of H2S in protic solvent was probed by NBD-SCN. It may suggest that DNIC can be a role for H2S storage and transport in hydrophobic environment. This phenomenon is attributed to the characteristic of non-innocent NO to regulate electron transfer among [FeIII-SH] core, which inhibited the reduction of FeIII into FeII and prevent reductive elimination of Fe-SH bond, The electronic structure containing [FeIII-SH] motif of complex 1, 1-PPN, 4 was determined by EPR, IR, XAS, and XRD. Complex 1 and 1-PPN can be described as high-spin FeIII (SFe = 5/2) and two NO－(SNO = 1) antiferromagnetically coupled. The thermally unstable complex 3 spontaneously dimerize into the first structurally characterized FeIII-hydrosulfide complex [PPN]2[(μ-S)Fe(SH)(NO)]2 (4). The electronic structure can be described as two {FeIII(NO－)}7 antiferromagnetic coupled to yield S = 0 diamagnetic complex. From recently published paper, the thermally unstable [PPN][Fe(SH)4] (5) spontaneously dimerizes to form [PPN]2[(SH)Fe (μ-S)]2 (6). According to the experiment, the stability of complex 1, 3, and 5 is 1 > 3 > 5. The stability of the dimerized-form is 2 > 4 > 6. On the basis of DFT computation and reduction potential, NO serves as strong electron-donating ligand (compared to thiolate), which reduces the effective nuclear charge(Zeff) of the iron center and prevent complex 1 from dimerization. That is, the stability increases accompanied with the larger NO-coordinate ligands bound to the [FeIII-SH] motif.