title: Iron(III) bound by hydrosulfide anion ligands: NO-promoted stabilization of the [Fe(III)-SH] motif.
abstract: Spontaneous transformation of the thermally stable [HS](-)-bound {Fe(NO)2}(9) dinitrosyl iron complex (DNIC) [(HS)2Fe(NO)2](-) (1) into [(NO)2Fe(μ-S)]2(2-) (Roussin's red salt (RRS)) along with release of H2S, probed by NBD-SCN (NBD = nitrobenzofurazan), was observed when DNIC 1 was dissolved in water at ambient temperature. The reversible transformation of RRS into DNIC 1 (RRS → DNIC 1) in the presence of H2S was demonstrated. In contrast, the thermally unstable hydrosulfide-containing mononitrosyl iron complex (MNIC) [(HS)3Fe(III)(NO)](-) (3) and [Fe(III)(SH)4](-) (5) in THF/DMF spontaneously dimerized into the first structurally characterized Fe(III)-hydrosulfide complexes [(NO)(SH)Fe(μ-S)]2(2-) (4) with two {Fe(NO)}(7) motifs antiferromagnetically coupled and [(SH)2Fe(μ-S)]2(2-) (6) resulting from two Fe(III) (S = 5/2) centers antiferromagnetically coupled to yield an S = 0 ground state with thermal occupancy of higher spin states, respectively. That is, the greater the number of NO ligands bound to [2Fe2S], the larger the antiferromagnetic coupling constant. On the basis of DFT computation and the experimental (and calculated) reduction potential (E1/2) of complexes 1, 3, and 5, the NO-coordinate ligand(s) of complexes 1 and 3 serves as the stronger electron-donating ligand, compared to thiolate, to reduce the effective nuclear charge (Zeff) of the iron center and prevent DNIC 1 from dimerization in an organic solvent (MeCN).
authors.affiliation: Department of Chemistry and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University , Hsinchu 30013, Taiwan.
authors.forename: Chih-Chin
authors.initials: CC
authors.lastname: Tsou
authors.forename: Wei-Chun
authors.initials: WC
authors.lastname: Chiu
authors.forename: Chun-Hung
authors.initials: CH
authors.lastname: Ke
authors.forename: Jia-Chun
authors.initials: JC
authors.lastname: Tsai
authors.forename: Yun-Ming
authors.initials: YM
authors.lastname: Wang
authors.forename: Ming-Hsi
authors.initials: MH
authors.lastname: Chiang
authors.forename: Wen-Feng
authors.initials: WF
authors.lastname: Liaw
mesh_terms: D000838:Anions; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry*; D006862:Hydrogen Sulfide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry; D009603:Nitroso Compounds / Q000737:chemistry*
chemical_list: D000838:Anions; D005290:Ferric Compounds; D058085:Iron Compounds; D008024:Ligands; D009589:Nitrogen Oxides; D009603:Nitroso Compounds; D009569:Nitric Oxide; C106536:Roussin's red salt; C073661:dinitrosyl iron complex; D007501:Iron; D006862:Hydrogen Sulfide