Mercury, thiolate complexes

Reviews on mercury—thiolate complexes and their bio-relevance333 and complexes with steric-ally hindered thiolate ligands have been published.334... 

X-ray absorption spectroscopy is a powerful method to assess the structure of mercury thiolate complexes. X-ray Absorption Near Edge Structure (XANES) spectroscopy can cleanly differentiate Hg(0), Hg(I) and Hg(II) by the energy of the emission edge. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy provides information regarding the coordination number and Hg-S bond distances. Typically, the EXAFS spectrum can establish the coordination number (/.e., number of sulfur atoms) to within 20%. More important, the bond length precision is 0.01 A. Given that each increase of one... 

The oxidation of thiols on mercury and some other metals (M = Zn, Cd) can be used for the preparation of different bis-thiolate complexes M(SR2) [18]. 

Analogous, but less common, syntheses have employed the mercury(II)complexes 82 which provide cyclopropenethiones 78 (Z = S). The replacement of the thioalkyl substituent of compound 83 occurs upon treatment with a secondary amine and a limited range of aminothiocyclopropenthiones are available in excellent yields. Moreover, these same compounds result from reaction of the corresponding thiolate (84) with, for example, benzoyl or thionyl chloride (equation 32). Such compounds have possible application in medicine, as dyes and as agrochemicals. 

Thiolate has been described as a pseudo-halide (92), and a close structural correspondence exists between halide and thiolate complexes of Hg(II). It is therefore worthwhile to review several features of the vibrational spectroscopy of the Hg-X (X=C1", Br, and I") bond, which has been extensively studied (22). We focus in particular on Hg-Cl bonds in HgCl2, HgCl, and HgCl ", the three species of most relevance to mercury-thiolate chemistry. 

With simple Hg thiolates the structures of bis(ethanethiolato)mercury Hg(SEt)2321 and of the cysteamine complex [Hg S(CH2)2NH3 2]Cl2322 have reference character, as only weak or no secondary bonds are present, and therefore the central S—Hg—S entities can be considered to be unperturbed. In mercury bis(tri-t-butoxysilanethiolate) Hg[SSi(o-t-Bu)3], with a strictly linear S—Hg—S unit, two weak intramolecular O II g interactions obviously do not affect the bonding in this unit.323... 

Subscript (ads) denotes adsorption via a thiolate linkage, while (ps) stands for a physisorbed and/or adsorbed state via different interactions. However, large dimensions of the studied molecules and their amphiphilic nature make the surface reaction mechanism more complex than in case of cystine/cysteine. Interfacial microstructure plays an important role in the determination of the surface behavior of the adsorbed molecules. From the study on the charge-transfer kinetics, the transfer coefficient a was calculated as slightly less than 0.50, while the rate constant (based on Laviron s derivations [105]) was of the order of 10 s k The same authors [106] have shown earlier that the adsorption rate constant of porcine pancreatic phospholipase A2 at mercury via one of its disulfide groups is of the order of 10 s h... 

Zinc and cadmium complexes of the novel tripod ligand (145) have also been described.1087 The reaction of Hg(HL)2 (HL = 2-mercaptobenzoic acid, 146) with cadmium nitrate leads to the novel CdHgL species, in which the cadmium is bonded to the carboxylate oxygen atom, and the mercury to the thiolate sulfur.1088... 

Tripod ligands of the pyrazolyl/thioimidazolyl-borate offering N2S, NS2, and S3-donor sets were employed in the study of biologically relevant alkylations of the R-thiolate zinc complexes (R = ethyl-, benzyl-, phenyl-, and p-nitrophenyl).78 A review recently described the use of poly(mercaptoimidazolyl)-borate in the chelation of cadmium and mercury.107... 

The thiol group of Cys is the most reactive side residue. The thiolate anion is a potent nucleophile and the thiol is a week acid with pKj = 8.37. Cys serves as the active site residues of many oxidoreductases. Cys residues form complexes of varying stability with a variety of metal ions. It reacts with organic mercurials stoichiometiically. Thiol residues of Cys cross link to form disulfide bonds (cystine) in proteins. Thiols and disulfides undergo rapid exchange and redox reactions. 

SC6H4NH2. Many of these complexes have a polymeric structure and in the cases that the metal is linearly coordinated there are several possibilities of stabilization as M- S, Hg- Hg, M- N (in heterocyclic thiolates), intramolecular NH- -S, or intermolecular CH- N interactions or ti-ti stacking. For mercury other type of neutral complexes of the form [HgR(SC6H4NH2)]... 

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