Mercury bridging atoms

Since our initial report we have noted three other transition metal mercury complexes in which the mercury bridges two or more metal atoms, which have been reported as products from sodium amalgam reductions, (a) D. Duffy, K. Mackay, and B. Nicholson, J. Chem. Soc. Dalton Trans., 1981,381 (b) R. Jones, F. Real, and G. Wilkinson, J. Chem. Soc. Dalton Trans., 1981,126 (c) J. Deutsche, S. Fadel, and M. Ziegler, Angew Chem. Int. Ed. Engl. 16,704 (1977). 

Calculations indicate that mercury-bridged carbocations (termed mercurinium ions) such as those formed in this reaction retain much of the positive charge on the mercury moiety. Only a small portion of the positive charge resides on the more substituted carbon atom. The charge is large enough to account for the observed Markovnikov addition, but it is too small to allow the usual rapid carbon skeleton rearrangements that take place with more fully developed carbocations. 

The interaction of 4-phenyl-3-imidazoline-l-oxyl (13c) with PdCl2 led to cyclometalation product 116, a dinitroxide with halo gen-bridging atoms (Ovcharenko et al, 1979). The reaction of 13c with mercury salts... 

Finally, the stereodynamics of two mercury-containing metal clusters have been reported. The mercury-bridged osmium cluster [ (ju-H)(/i3-S) (C0)90s3 2(/i4-Hg)] exhibits variable-temperature NMR spectra which are attributed to movements of both fi-Hg and /i-H moieties at comparable rates. Mercury halides form adamantane-like anions with chalcogen bridges. The resulting structures [( i-ER)6(HgX)4] (E = S, Se, Te X = C1, Br, I) have been examined in solution by Se, Te, and Hg NMR spectroscopy. The species tend to dissociate in solution. Pyramidal inversions at Se and Te atoms are slow on the NMR time scale at reduced temperatures, but tend to become rapid at ambient temperatures. ... 

Zinc dithiocarbamates have been used for many years as antioxidants/antiabrasives in motor oils and as vulcanization accelerators in rubber. The crystal structure of bis[A, A-di- -propyldithio-carbamato]zinc shows identical coordination of the two zinc atoms by five sulfur donors in a trigonal-bipyramidal environment with a zinc-zinc distance of 3.786 A.5 5 The electrochemistry of a range of dialkylthiocarbamate zinc complexes was studied at platinum and mercury electrodes. An exchange reaction was observed with mercury of the electrode.556 Different structural types have been identified by variation of the nitrogen donor in the pyridine and N,N,N, N -tetra-methylenediamine adducts of bis[7V,7V-di- .vo-propyldithiocarbamato]zinc. The pyridine shows a 1 1 complex and the TMEDA gives an unusual bridging coordination mode.557 The anionic complexes of zinc tris( V, V-dialkyldithiocarbamates) can be synthesized and have been spectroscopically characterized.558... 

The chemisorption of species occurs at specific sites on the electrode, for example on top of certain atoms, or in the bridge position between two atoms. Therefore, most adsorption studies are performed on well-defined surfaces, which means either on the surface of a liquid electrode or on a particular surface plane of a single crystal. Only fairly recently have electrochemists learned to prepare clean single crystal electrode surfaces, and much of the older work was done on mercury or on amalgams. 

The X-ray crystal structures of the related, though less complex, anticrown mercury-containing macrocycles 45 and 46 have also recently been reported. Complex 45 may form either 1 1 complexes with Br or I" or a 3 2 complex with Cr. In the case of the bromo derivative, crystallographic results reveal an infinite chain of alternating Br and 45 with each halide bridging between six Hg atoms, Hg- Br 3.07-3.39 A. It is postulated that the related 3 2 chloride complex exhibits a similar, though finite layered structure. The related pentameric species 46 forms... 

Reaction of l,l -di(chloromercuri) ferrocene with sodium iodide or sodium thiosulfate might be expected to lead to higher homologs of XXIX in which ferrocene units are bridged by atoms of mercury. Reactions of this type have produced apparently polymeric materials with structures such as XXX, although the very limited solubility of the products has thus far precluded reliable molecular weight measurements (80). 

Bridge mediation mechanisms in heterogeneous outer sphere electrochemical reactions has also been theoretically treated using the pull—push and push-pull mechanistic concepts [84]. Schmidt [85] has considered theoretically homogeneous inner sphere bridge electron transfer reactions without atom or ion transfer. Bridge mediation in electron transfer reactions may also involve simultaneous atom or ion transfer. Heyrovsky [86] invoked mediation of electron transfer by formation of bridges to explain the enhancement of the rate of electroreduction of indium (III) ions in the presence of specifically adsorbed halide ions on mercury. 

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