Iron(III) bound by hydrosulfide anion ligands: NO-promoted stabilization of the [FeIII-SH] motif

Chih Chin Tsou*, Wei Chun Chiu, Chun Hung Ke, Jia Chun Tsai, Yun-Ming Wang, Ming Hsi Chiang, Wen Feng Liaw

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


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) ]22- (Roussins 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 H 2S was demonstrated. In contrast, the thermally unstable hydrosulfide-containing mononitrosyl iron complex (MNIC) [(HS) 3FeIII(NO)]- (3) and [FeIII(SH) 4]- (5) in THF/DMF spontaneously dimerized into the first structurally characterized FeIII-hydrosulfide complexes [(NO)(SH)Fe(μ-S)]22- (4) with two {Fe(NO)}7 motifs antiferromagnetically coupled and [(SH)2Fe(μ-S)] 22- (6) resulting from two FeIII (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).

Original languageEnglish
Pages (from-to)9424-9433
Number of pages10
JournalJournal of the American Chemical Society
Issue number26
StatePublished - 2 Jul 2014

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