Mercury complexes sulfur ligands

The divalent state of mercury (Hg ) dominates in most natural water however, elemental Hg° is the most stable form in a broad pE/pH range. Hg forms very strong complexes with oxygen and sulfur ligands, as well as with chloride. A significant hydrolysis starts at pH> 1 and dominates at pH >2, in the absence of other complexing agents. The chloride... 

Mercury(II) is a very soft Lewis acid, which forms stable complexes preferentially with soft Lewis bases such as sulfur ligands. You should remember here that the major natural form of mercury is sulfides. Increasing the pH of the aqueous solution due to... 

Mercury(ll) is a very soft Lewis acid, which forms stable complexes preferentially with soft Lewis bases such as sulfur ligands. You should remember here that the major natural form of mercury is sulfides. Increasing the pH of the aqueous solution due to pollution or river water discharge to marine water leads to precipitation of HgO. We know that HgO has finite solubility in water, and the solution may be described in terms of mercury(II) hydroxide as the following reactions (2)-(4)... 

Similar unfavorable constants can be obtained for the other cases. A successful agent in complexing the Hg(II) is BAL (British anti-Lewisite), 2,3-dimercaptopropanol, with potent sulfur ligands for the mercury, and also for arsenic, antimony, bismuth, and gold. It is injected intramuscularly in 10% solution in peanut oil at a dose rate of 3 mg/kg of body weight every 4 hr for two days, and after that at decreasing frequency until recovery. 

Complexes of Mercury(l) with Sulfur- and Selenium-Donor Ligands. 

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... 

The complex Na2Hg(S03)2-H20 has been prepared. It contains discrete Hg(S03)2 anions with S-bonded S03 units (Hg—S = 240.2,241.1 pm).393,394 Mercury(II) thiosulfate complexes obtained in solution also appear to be S bonded.395 Mercury(II) forms numerous compounds with different sulfur donor ligands. Many of them have been reviewed by McAuliffe7 and by Constable.5... 

The mercury atom is surrounded by four sulfur donor atoms from two centrosymmetrically related Et2Dtc ligands. A linear coordination is found for the Hg(II) ion with two short Hg-S bonds at 2.397(6) A. The remaining sulfurs are found at 2.990(7) A. As in the structure of the As(Et2 Dtc)3 complex (124), the two MS bond lengths are different for each of the two ligands and the C—S distance shows an inverse relation to the M-S distance. 

Today the predominant if not the sole source of methylmercury is derived from the methylation of inorganic mercury in aquatic sediments and soils. Methylmercury is well absorbed from the diet and distributes within a few days to all tissues in the body. It is present in the body as water-soluble complexes mainly, if not exclusively, attached to the sulfur atom of thiol ligands, and crosses the blood—brain barrier without hindrance, entering the endothelial cells of the blood—brain barrier as a complex with L-cysteine. The principal target tissue of MeHg is the brain, and its major toxic effects are on the central nervous system. Whereas adult poisoning affects the visual cortex and the cerebellum, in neonatal infants the outcome can be much more serious, ranging in its effects from cerebral palsy to developmental retardation. 

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