Unprecedented stabilization of cobalt(II) in a tetrahedral S2O2 environment: The use of a redox-noninnocent ligand

The reaction of Zn(II) and Co(II) with thiosalicylic acid, o-HSC6H4COOH, an d its methyl ester has led to the following complexes: [Zn(SC6H4COO)] (1), (NEt4)Na[Zn(SC6H4COO)(2)].H2O (2), (NEt4)(2)Na[Co(SC6H4COO)(3)].2H(2)O (3), (NEt4)(3)Na-3[{Co(SC6H4COO)(3)}(2)].6MeOH (4), [Zn(SC6H4COOMe)(2)] (5), an d [Co(SC6H4COOMe)(n)], n = 2 (6), 3 (7). These ligands have not allowed sta bilization of Co(II) in a sulfur-oxygen coordination environment. The struc tures of complexes 2-4 and 7 have been determined crystallographically. Tho se of 2-4 show significant similarities such as the behavior of the -SC6H4C OO- anion as chelating ligand and the involvement of sodium ions as a struc tural element. Thus, the structure of the [Na{Zn(SC6H4COO)(2)}(H2O)](-) ani on in complex 2 can be described as infinite chains of consecutive [Zn(SC6H 4COO)(2)](2-) metalloligands linked by [Na(H2O)](+) centers, that of the [N a{Co(SC6H4COO)(3)(H2O)(2)}](2)(4-) anion in 3 as a centrosymmetric tetranuc lear Co2Na2 dimer with a {Co-III(S boolean ANDO)(3)}Na(mu -H2O)(2)Na{Co-III (S boolean ANDO)(3)} core, and that of the pentanuclear [Na-3{Co(SC6H4COO)( 3)}(2)(MeOH)(6)](3-) anion in 4 as two dinuclear [{Co-III(S boolean ANDO)(3 )}Na(MeOH)(3)] fragments linked to a central sodium ion, which appears to b e the first structurally characterized example of a NaS6 site. The use of t he o-HSC6H4COOMe ligand allowed the synthesis of [Co(SC6H4COOMe)(2)] (6) bu t not its full structural characterization. Instead, [Co(SC6H4COOMe)(3)] (7 ) was obtained and structurally characterized. It consists of mononuclear m olecules containing an octahedral (CoS3O3)-S-III core. The selection of 2,2 -diphenyl-2-mercaptoacetic acid as ligand with reductive properties has aff orded the first mononuclear complex containing a (CoS2O2)-S-II core and thu s an unprecedented model for Co(II)-substituted metalloproteins containing tetrahedral MS2O2 active sites. The synthesis and full structural character ization 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{Ph2 C(S)COO}(2)](2-) anions, with a distorted tetrahedral coordination about th e metal. In addition, the stability conferred by the ligand on the (CoS2O2) -S-II core has allowed its characterization in solution by paramagnetic 1D and 2D H-1 NMR studies. The longitudinal relaxation times of the hyperfine- shifted resonances and NOESY spectra have led to the assignment of all reso nances of the cobalt complex and confirmed that it maintains its tetrahedra l geometry in solution. Magnetic measurements (2-300 K) for complex 9 and 9 .2H(2)O are in good agreement with distorted tetrahedral and octahedral env ironments, respectively.