Unprecedented stabilization of cobalt(II) in a tetrahedral S<inf>2</inf>O<inf>2</inf> environment: The use of a redox-noninnocent ligand

N. Duran, W. Clegg, L. Cucurull-Sanchez, R. A. Coxall, H. R. Jimenez, J. M. Moratal, F. Lloret, P. Gonzalez-Duarte

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Abstract

The reaction of Zn(II) and Co(II) with thiosalicylic acid, o-HSC6H4COOH, and its methyl ester has led to the following complexes: [Zn(SC6H4COO)] (1), (NEt4)Na[Zn(SC6H4COO)2]·H2O (2), (NEt4)2Na[Co(SC6H4COO)3]·2H2O (3), (NEt4)3Na3[{Co(SC6H4COO)3}2]·6MeOH (4), [Zn(SC6H4COOMe)2] (5), and [Co(SC6H4COOMe)(n)], n = 2 (6), 3 (7). These ligands have not allowed stabilization of Co(II) in a sulfur-oxygen coordination environment. The structures of complexes 2-4 and 7 have been determined crystallographically. Those of 2-4 show significant similarities such as the behavior of the -SC6H4COO- anion as chelating ligand and the involvement of sodium ions as a structural element. Thus, the structure of the [Na{Zn(SC6H4COO)2}(H2O)]- anion in complex 2 can be described as infinite chains of consecutive [Zn(SC6H4COO)2]2- metalloligands linked by [Na(H2O)]+ centers, that of the [Na{Co(SC6H4COO)3(H2O)2}]24- anion in 3 as a centrosymmetric tetranuclear Co2Na2 dimer with a {Co(III)(S intersection set O)3}Na(μ-H2O)2Na{Co(III)(S intersection set O)3} core, and that of the pentanuclear [Na3{Co(SC6H4COO)3}2(MeOH)6]3- anion in 4 as two dinuclear [{Co(III)(S intersection set O)3}Na(MeOH)3] fragments linked to a central sodium ion, which appears to be the first structurally characterized example of a NaS6 site. The use of the o-HSC6H4COOMe ligand allowed the synthesis of [Co(SC6H4COOMe)2] (6) but not its full structural characterization. Instead, [Co(SC6H4COOMe)3] (7) was obtained and structurally characterized. It consists of mononuclear molecules containing an octahedral Co(III)S3O3 core. The selection of 2,2-diphenyl-2-mercaptoacetic acid as ligand with reductive properties has afforded the first mononuclear complex containing a Co(II)S2O2 core and thus an unprecedented model for Co(II)-substituted metalloproteins containing tetrahedral MS2O2 active sites. The synthesis and full structural characterization of the isostructural complexes (NEt4)2[Zn{Ph2C(S)COO}2] (8) and (NEt4)2[Co{Ph2C(S)COO}2] (9) show that they consist of discrete [M{Ph2C(S)COO}2]2- anions, with a distorted tetrahedral coordination about the metal. In addition, the stability conferred by the ligand on the Co(II)S2O2 core has allowed its characterization in solution by paramagnetic 1D and 2D 1H NMR studies. The longitudinal relaxation times of the hyperfine-shifted resonances and NOESY spectra have led to the assignment of all resonances of the cobalt complex and confirmed that it maintains its tetrahedral geometry in solution. Magnetic measurements (2-300 K) for complex 9 and 9·2H2O are in good agreement with distorted tetrahedral and octahedral environments, respectively.
Original languageEnglish
Pages (from-to)4821-4832
JournalInorganic Chemistry
Volume39
Issue number21
DOIs
Publication statusPublished - 16 Oct 2000

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