Mercury complex, bond length

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. 

The first mercury(I) silyl complex [(Me3SiMe2Si)3Si]2Hg2 was prepared by the reaction of an excess of (Me3SiMe2Si)3SiH with (t-Bu)2Hg. The solid structure of the complex displays linear Si—Hg—Hg—Si fragment with regular metal-silicon bond lengths... 

Note The cationic mercury(II) carbene complex in Figure 3.74 shows Hg-0 distances that are consistent with Hg-0 bond lengths in mercury crown ether complexes [212]... 

Bacterial mercuric reductase is a unique metal-detoxification biocatalyst, reducing mercury(II) salts to the metal. The enzyme contains flavin adenine dinucleotide, a reducible active site disulfide (Cys 135, Cys i4o), and a C-terminal pair of cysteines (Cys 553, Cys 559). Mutagenesis studies have shown that all four cysteines are required for efficient mercury(II) reduction. Mercury Lm-EXAFS studies for mercury(II) bound to both the wild-type enzyme and a very low-activity C-terminal double-alanine mutant (Cys 135, Cys uo, Ala 553, Ala 559) suggest the formation of an Hg(Cys)2 complex in each case (39). The Hg—S distances obtained were 2.31 A and are consistent with the correlation of bond length with coordination number presented above. Thus, no evidence was obtained for coordination of mercury(II) by all four active-site cysteines in the wild-type mercuric reductase. However, these studies do not define the full extent of the catalytic mechanism for mercury(II) reduction, and it is possible that a three- or four-coordinate Hg(Cys) complex is a key intermediate in the process. 

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... 

In the above manner, in dimethyl sulphoxide and dimethylformamide solutions of mercury (II) iodide-sodium iodide systems of various compositions, Gaizer and Johansson [Ga 69] determined the Hg—I bond lengths and also the I—I distances for the dissolved complexes Hgll", Hgl and Hgl2, and from these data conclusions were drawn about the symmetries of the species. 

Cd-Cd- and Hg-Hg-bonded complexes can also be synthesized by reacting diaryl cadmium or diaryl mercury with the intermetallic Zintl phases K Pb, or Kj As, respectively (method xiii. Scheme 12.5) [30]. In both cases, a Zind duster anion ([Pb CdCdPh,] " or [As HgHgAs ] ") is formed in which the metal atoms are connected by a single bond (16-17, Scheme 12.9). Complex 16 crystallized as two crystallographically independent molecules in which the Cd-Cd bond length is 2.697(1) and 2.715 (2) A, respectively, while the Hg-Hg bond distance in 17 is 2.6792(9) A. 

Even G12-Tc-bonded complexes have been prepared. The tris(arylimido)technitium anion (90) reacted readily with 0.5 or 1 equiv. of HgBr2 to afford [Hg Tc(NAr)3 2] (91) or [BrHgTc(NAr)3] (Ar = 2,6-diisopropylphenyl) (92), respectively (Scheme 12.29) [70]. The crystal structure of Hg[Tc(NAr)3]2 shows a linear geometry around the mercury atom and the bond length of Tc-Hg is 2.615(1) A. Also the rhenium analog [Hg Re(NAr)3 2] (93) was obtained through reduction of tris(arylimido)rhenium chloride with sodium amalgam (Scheme 12.29) [70]. 

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