Mercury direct bonding

In cinnabar, HgS, the sulfur atom has a normal-valence structure, in which it forms two bonds with mercury atoms. The Hg—S—Hg bond angle is 105°. The mercury atom may be described as forming two oppositely directed bonds with use of two sp hybrid bond orbitals the value of the S—Hg—S angle is 172°. The bond length, 2.36 A, leads,... 

The 13C spectra of some (3-methoxyalkyl mercuric chlorides have been reported.175 The results indicate that (Hg-C) ( 1600—1800 Hz) varies in direct proportion to the increase in electron density at the mercury-carbon bond, and that an increase in mercury-carbon alkyl substitution, an effect which is in direct contrast to that observed for platinum 7r-olefin complexes. 

Mercury will bond directly to certain metal atoms including Co, Ru, Rh, Fe, Pt, and Mn. Such Hg-metal bonds are usually part of linear M-Hg-M or M-Hg-X linkages, and some clusters containing mercury-metal bonds are also known. These compounds are prepared by the reaction of mercury(II) halides with carbonyhnetallates. A rare example of trigonal prismatic (see Trigonal Prism) coordination in a mercury complex is exhibited by [Hg Pt3(2,6-Me2C6H3NC)6 2], which contains Pt-Hg bonds. These types of compound have been reviewed. ... 

Introduction Anions have a strong tendency to adsorb specifically at metal surfaces, for example, to estabKsh a direct bond with the electrode by partial loss of their hydration shell. As a consequence of the contact with the electrode, the ionic character of the anions is markedly reduced, resulting in a higher surface concentration than in case of nonspecific adsorption. This effect was first observed in double-layer studies on mercury [229, 230] and later confirmed and studied in detail on single-crystal solid electrodes [231-234]. Specifically adsorbed anions can form various types of ordered structures, either more open (cf. sulfate on Au(hld) [235, 236]) or close-packed as reported for halides on different solid electrodes [21]. Cyclic current-potential curves often reveal sharp current peaks, indicative of phase transitions within the anionic adlayers and hence of the existence of ordered phases [21, 237]. Thermodynamic data of specific anion adsorption was obtained in surface tension studies (on mercury only [229,238-240]), capacitance measurements [231-233], cyclic voltammetry, and chronocoulometry [234]. As an... 

The four-membered ring unit Hg2Cl2 can occur as a part of a ladder structure. Thus, (2-pyridylphenyl)mercury(II) chloride, 15a, is a tetramer, with the skeleton shown in 15b (only atoms directly bonded to mercury are shown for clarity). The mercury-chlorine interatomic distances are in the range 3.184-3.442 A [75]. 

Mercury has a characteristic ability to form not only conventional ammine and amine complexes but also, by the displacement of hydrogen, direct covalent bonds to nitrogen, e.g. ... 

The reaction has also been used to prepare 1,3-dilithiopropanes" and 1,1-dilithio-methylenecyclohexane" from the corresponding mercury compounds. In general, the equilibrium lies in the direction in which the more electropositive metal is bonded to that alkyl or aryl group that is the more stable carbanion (p. 228). The reaction proceeds with retention of configuration an Sgi mechanism is likely. Higher order cuprates (see Ref. 1277 in Chapter 10) have been produced by this reaction starting with a vinylic tin compound ... 

At the platinum electrode the individual steps of the four-electron reaction cannot be studied separately. Slope b has its usual value of about 0.12 V, but in contrast to what is seen at the mercury electrode, the polarization is practically independent of solution pH (i.e., the potential at a given current density shifts by 0.06 V in the negative direction when the pH is raised by a unit). It follows that the reaction rate depends on hydrogen ion concentration. The step in which an electron and a proton are transferred while the 0-0 bond is broken is probably the ratedetermining step. 

Organomercury reagents do not react with ketones or aldehydes but Lewis acids cause reaction with acyl chlorides.187 With alkenyl mercury compounds, the reaction probably proceeds by electrophilic attack on the double bond with the regiochemistry being directed by the stabilization of the (3-carbocation by the mercury.188... 

These investigators also observed that cleavage of the carbon-sulfur bond of aryl sulfones, a very difficult process to carry out by other means, proceeds smoothly at a mercury electrode even with sterically hindered sulfones, although the direction of cleavage of the latter appears to be governed by steric considerations, e.g. 11 >,... 

Bond et al. [791 ] studied strategies for trace metal determination in seawater by ASV using a computerised multi-time domain measurement method. A microcomputer-based system allowed the reliability of the determination of trace amounts of metals to be estimated. Peak height, width, and potential were measured as a function of time and concentration to construct the database. Measurements were made with a potentiostat polarographic analyser connected to the microcomputer and a hanging drop mercury electrode. The presence of surfactants, which presented a matrix problem, was detected via time domain dependent results and nonlinearity of the calibration. A decision to pretreat the samples could then be made. In the presence of surfactants, neither a direct calibration mode nor a linear standard addition method yielded precise data. Alternative ways to eliminate the interferences based either on theoretical considerations or destruction of the matrix needed to be considered. 

In the capillaries of variable cross section or the lattice of the interconnected sites and bonds of the various size the situation is essentially different. At the beginning, the mercury is at the external surface of particles of a sample, and only the pores that are directly contiguous to external surface can be filled according to the considered model of a bunch of capillaries. The cavities with windows of size rw (F>HgX which are adequate to an equilibrium condition but inside the bulk of a sample, can be filled only under a condition of their connection to an external surface through a circuit of cavities with windows of size V > rwP already filled with mercury. Therefore, the condition for the filling of a cavity with a window of the size rm can be expressed as the requirement of a direct contact of a considered cavity with mercuiy. Accordingly, under each pressure PHg, all windows of size rWl are only poten-... 

Considering that /Tarninornercury(II) tetrafluoroborates are polar enough to undergo nucleophilic attack by the lone electron pair of an amine, ether or alcohol in the case of the 1,3-cyclooctadiene, 179, it has been assumed that the first formed 1,4-adduct can give the reaction product by displacement of mercury by amine with direct participation of the nucleophile in an assisted breakage of the anti C—Hg bond (path a) or by spontaneous reduction of mercury in the intermediate allylic organomercurial (path b) (equation 157). 

An alternative hypothesis, that the reaction product arises from a first formed 1,2-adduct, from which the same ionic intermediate may be generated (equation 158), has been ruled out by considering the directive effect of the conjugated double bonds on oxymercuration, which favors the attack of mercury at the terminal positions of conjugate 7r-systerns. 

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