Linear mercury compounds

There are mercury compounds with mercury oxidation numbers lower than +1, e.g. +0.5,16,21 +0.6713,15,27 or +0.35.18,20 Yellow crystals of Hg3(AsF6)2 have been formed by the reaction of metallic mercury with AsFs in liquid S02.13 X-Ray structure determination showed a linear polycation Hg+—Hg—Hg+ with Hg—Hg distances of 255 pm.15 Metallic mercury and SbF5 react in liquid S02 to form Hg3(Sb2Fu)2.15,23 The Hg—Hg distances in the complex Hg3(AlCU)2 are 256 pm 14 the Hg—Cl distances are 251 and 256 pm the Hg—Hg—Hg angle is 174°. Dark red crystals of Hg4(AsF6)2 were obtained in liquid S02. This coordination compound contains centrosymmetric Hg4+ ions, which are connected to chains (see l).21... 

In the gas phase, divalent mercury has been shown to be linear and therefore to be sp hybridized. However, in solution the X—R—X, R—Hg—X, or R—Hg—R bond angle in divalent mercury compounds varies from 130 to 180°. The variation in geometry is not yet entirely understood, so we shall follow Jensen s example and assume that, even in solution, divalent mercury is sp hybridized and that if a divalent mercury compound donates one empty orbital to coordinate with a Lewis base it rehybridizes to sp2 (F. R. Jensen and B. Rickborn, Electrophilic Substitution of Organomercurials, pp. 35, 36). 

Linearly connected polycyclic silanes are usually made by salt elimination reactions, whenever the cyclosilanyl alkali metal compound involved is stable enough. Otherwise, the photochemical cleavage of bis(cyclosilanyl)mercury compounds may be employed. An... 

In order to understand the biochemistry of mercury more completely, it is important to describe the chemistry of this element with sulfhydryl donors in the most common coordination environments. Ideally, one would examine mercuric complexes within a construct that was basically invariant, but which allowed for preparation of mercury compounds in the most common structures. The desired coordination modes include linear (or slightly bent) for 2-coordinate complexes, trigonal planar (or slightly T-shaped) for 3-coordinate compounds and tetrahedral for 4-coordinate complexes. Figure 1. Unfortunately, diere are no known native systems that allow for this diversity of metal coordination geometry. However, given advances in peptide synthesis and the prediction of... 

Table tr.1-175 Linear thermal expansion coefficient a of mercury compounds ... 

When the dependence of log(iiim — i) with potential is linear and the slope is RT X 2-303/ F, an insoluble product of the electrode reaction is formed. Such curves, resulting in sharp bends, were observed for some anodic waves corresponding to a formation of an insoluble mercury compound, e.g. diethylbar-bituric acid.< >... 

Oxidation numbers for Hg (I) and (II), as in Hg20, mercurous oxide, HgO, mercuric oxide, and Hg 0 2 [mercuiy(ll) peroxide]. The mercurous ion is dimercury(2+) or dimercury(I), Hg2. Relativity greatly strengthens the Hg-Hg bond but may also explain the metal s liquidity. Relativity shrinks and stabilizes mercury s 6s orbital, making Hg rather like a noble gas but favoring linear sp hybrids with more (1/2 s) low-energy s nature than the tetrahedral sp (1/4 s). The many (linear) oigano-mercury compounds are excluded here. 

Table 4. Chemical Shifts of Linear Mercury(II) Compounds, HgX2...

Linear organomercurials provide a convenient basis for the investigation of the effect of substitution in the organic moiety on the metal chemical shift. In view of significant solvent effects, it is desirable to measure any such series of compounds in more than one solvent. Increases in the shielding of ca. 150 ppm are observed for each substitution of Me for an a-H in Hg-CHj derivatives, while smaller decreases in shielding (ca. 30 ppm) occur on substitution of ) -H s. Cadmium alkyls seem to show a similar behavior, but for silyl mercury compounds, replacements at both a and P positions result in deshielding. ... 

There is also an old report of a dimeric complex, Au°2(PPh3)2, that was formed by reduction of ClAu CPPhj) [17], This compound, which has a short Au-Au bond, is an analog of mercury compounds like linear Hg2Cl2. Oddly, however, this crystallographic study indicated that this complex had P-Au-Au angles that were strongly bent. Details of this work have not been published, and the compound warrants reinvestigation. 

It appears that all RHgX and HgR2 compounds are made up of linear R-Hg-X or R-Hg-R units, which could arise from sp hybridization of the metal. In some cases polymerization is necessary to achieve this linearity. Thus, for instance, o-phenylene-mercury, which could conceivably be formulated as... 

Berberine is an alkaloid undergoing an irreversible four-electron and three-proton reduction to the electrochemically inactive compound canadine, which is also adsorbed on the mercury electrode surface. As predicted by the theory, the net peak current of berberine is a linear function of the frequency, whereas the peak current shifts linearly with log(/) with a slope of -45 mV. Based on the theoretically predicted value for the half-peak width, AE p/2 = (63.5 0.5) / c mV, the catho-... 

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