Cadmium, and Mercury

Cadmium, and Mercury.—Slurries of finely divided Cd or Zn, formed by codeposition of the appropriate metal vapour with a solvent, are active enough to form organometallic reagents (presumed to be metal dialkyls) by reaction with simple alkyl halides. Not only a-bromoesters, but also a-bromoketones, can be reacted with Zn to give Reformatsky-like reagents. Subsequent reaction with an 

Frangin and M. Gaudemar, Bull. Soc. chim. France, 1976, 1173 Y. Frangin, E. Favre, 

At elevated temperatures ca. 200 °C) many aienes can be permercurated with Hg(OCOCp3)2 and thus converted into perbromo-derivatives.  

Cadmium, and Mercury - NMR spectroscopy has been used to investigate rotation about the N-C(O) bond in Me2NC(0)Bu coordinated to 1,2-phenylenedimercury bis(trifluoroacetate). NMR spectroscopy has been used to demonstrate restricted rotation in a zinc porphyrin linked by s-tri(4-pyridyl)triazine. and N NMR spectroscopy has been used to study 

Fuchita, H. leda, Y. Tsunemune, J. Kinoshita-Nagaoka, and H. Kawano, J. Chem. Soc., Dalton Trans., 1998, 791. 

This chapter reviews the bioinorganic and inorganic co-ordination chemistry of the Group IIB elements from September 1975 to September 1976. As a change from the previous two years, the chemistry of these elements is discussed here in terms of the donor ligand involved, rather than the individual metals themselves. 

Structure determinations of the ZnClJ ion as its MeNH and Ni(CH3CN)g salts show only slight distortions from perfect tetrahedral symmetry (Zn—Cl = 

These three elements follow copper, silver and gold and have two s electrons outside filled d shells. Some of their properties are given in Table 18-1. Whereas in Cu, Ag and Au the filled d shells may lose one or 

Outer configuration Ionization potentials, eV 3rf104s2 4dl05s2 5dl06s2 

Divergence from the Group valence does occur, however, in the ions M, of which only Hgf+ is ordinarily stable, and Hg + (w = 3—6), as discussed below. There are no simple M + ions with a single s electron in this Group or for any of the elements of the first, second, or third long Periods. Where such ions might have been expected, there is either disproportionation as in 

Gau- Ga +Ga111 (page 279) or formation of a metal—metal bond as in Ga2S2 and Hg2+. 

The stereochemistry of the elements in the II state is summarized in Table 18-2 the nature of Hg2 + compounds is discussed below. Since there is no ligand field stabilization effect in Zn2+ and Cd2+ ions because of their completed d shells, their stereochemistry is determined solely by considerations of size, electrostatic forces, and covalent bonding forces. The effect of size is to make Cd2 + more likely than Zn2 + to assume a coordination number of six. For example, ZnO crystallizes in lattices where the Zn2+ ion is in tetrahedral holes surrounded by four oxide ions, whereas CdO has the rock 

Although a number of structures have been reported for analogous compounds of both elements, these are in the minority, and it is perhaps most convenient to consider the two elements separately for each co-ordination number. The order of discussion within each subdivision is roughly that of increasing size of ligand atom. 

As expected, the majority of zinc compounds have the metal in tetrahedral co-ordination, whUst those of cadmium adopt mostly octahedral geometry. Exceptions do occur in each case, however. 

A rather special type of tetrahedral geometry is found for zinc in 

A structure in which the Zn atom might be expected to show some ionic character is willemite, ZnjSiOi, for which the high-pressure phase has been 

Similarly, in zinc diborate, the packing requirements of the larger diborate ion cause large distortions in the tetrahedral environment of the zinc ions Zn-O distances range from 1.984 to 2.045 A and angles from 89.1 to 125.3°. 

Group lib of the periodic table includes two very important ele ments, zinc and mercury, and one element, cadmium, which has four d rather limited use. 

The chemistry of these metals is simple. Zinc forms only one series of compounds, in which the metal is bipositive (Zn++, ZnO, etc.). The compounds of cadmium are closely similar to those of zinc, represent ing only oxidation number -f2. Mercury forms two series of com pounds the mercuric compounds, which contain bipositive mercury (Hg+ +, HgCU, HgS, etc.), and the mercurous compounds, which contain unipositive mercury (Hg + +, HgXL, etc.). 

Zinc is also used in making alloys, the most important of which is brass (the alloy with copper), and as a reacting electrode in dry cells and wet cells. 

TABLE 28 L SOME PHYSICAL PROPERTIES OF ZINC, CADMIUM. AND MERCURY 

Mercury is the only metal which is liquid at room temperature (cesium melts at 28.5 C, and gallium at 29.8°). It is iinreacrive, being below hydrogen in the electromotive-force series. Because of its unreactivity, fluidity, high density, and high electrical conductivity it finds extensive use in thermometers, barometers, and many special kinds of scientific Apparatus. 

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Group IIB and know that this means the group of elements zine. cadmium and mercury, whilst Group IIA refers to the alkaline earth metals beryllium, magnesium, calcium, barium and strontium. 

Unlike cadmium and mercury and, in fact, all metals of Group II, zinc dissolves readily in alkalis forming zincates. in which the zinc atom is contained in a complex hydroxo-anion, for example ... 

Zn(C2Hs)2 -E 2H2O Zn(OH)2 -E (Cadmium and mercury also form alkyls.)... 

These elements formed Group IIB of Mendeleef s original periodic table. As we have seen in Chapter 13, zinc does not show very marked transition-metaf characteristics. The other two elements in this group, cadmium and mercury, lie at the ends of the second and third transition series (Y-Cd, La-Hg) and, although they resemble zinc in some respects in showing a predominantly - - 2 oxidation state, they also show rather more transition-metal characteristics. Additionally, mercury has characteristics, some of which relate it quite closely to its immediate predecessors in the third transition series, platinum and gold, and some of which are decidedly peculiar to mercury. 

Cadmium and mercury are usually recovered ia separate processes at the ziac plant. The others are shipped as enriched residues to plants that specialize ia their recovery. 

In recent years, environmental contamination by lead, cadmium, and mercury has been repeatedly observed and has given rise to partly exaggerated reports. 

Table 29.1 Some properties of the elements zinc, cadmium and mercury...

J. L. Wardell, Organometallic Compounds of Zinc, Cadmium and Mercury, Chapman Hall, London, 1985,... 

The elements in Groups 3 through 11 are called the transition metals because they represent a transition from the highly reactive metals of the s block to the much less reactive metals of Group 12 and the p block (Fig. 16.1). Note that the transition metals do not extend all the way across the d block the Group 12 elements (zinc, cadmium, and mercury) are not normally considered to be transition elements. Because their d-orbitals are full, the Group 12 elements have properties that are more like those of main-group metals than those of transition metals. Just after... 

Metallothioneins are a group of small proteins (about 6.5 kDa), found in the cytosol of cells, particularly of liver, kidney, and intestine. They have a high content of cysteine and can bind copper, zinc, cadmium, and mercury. The SH groups of cysteine are involved in binding the metals. Acute intake (eg, by injection) of copper and of certain other metals increases the amount (induction) of these proteins in tissues, as does administration of certain hormones or cytokines. These proteins may function to store the above metals in a nontoxic form and are involved in their overall metaboHsm in the body. Sequestration of copper also diminishes the amount of this metal available to generate free radicals. 

Calabrese A, Thurberg FP, Dawson MA, WenzlofF DR. 1975. Sublethal physiological stress induced by cadmium and mercury in the winter flounder (Pseudoplumnectes amer-icanus). In Koeman JH, Strik JJ, editors, Sublethal effects of toxic chemicals on aquatic animals. Amsterdam Elsevier. 

Nicholson JK, Osborn D. 1983. Kidney lesions in pelagic seabirds with high tissue levels of cadmium and mercury. J Zool London 200 99-118. 

Tsuchiya W, Okada Y. 1982. Differential effects of cadmium and mercury on amino acid and sugar transport in the bullfrog small intestine. Experientia (Basel) 38 1073-1075. 

Rabinovich D (2006) Poly(mercaptoimidazolyl)borate Complexes of Cadmium and Mercury 120 143-162... 

Baldrian, P., der Wiesche, C., Gabriel, J., Nerud, E, and Zadrazil, F., Influence of cadmium and mercury on activities of ligninolytic enzymes and degradation of polycyclic aromatic hydrocarbons by Pleurotus ostreatus in soil, Appl Environ Microbiol, 66 (6), 2471-2478, 2000. 

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures nylon and polypropylene, for use in manufacturing the cell separators and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.1-4 A typical example is the nickel-cadmium battery described below. 

Cadmium (Cd) anode cells are at present manufactured based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples. Thus wastewater streams from cadmium-based battery industries carry toxic metals cadmium, nickel, silver, and mercury, of which Cd is regarded the most hazardous. It is estimated that globally, manufacturing activities add about 3-10 times more Cd to the atmosphere than from natural resources such as forest fire and volcanic emissions. As a matter of fact, some studies have shown that NiCd batteries contribute almost 80% of cadmium to the environment,4,23 while the atmosphere is contaminated when cadmium is smelted and released as vapor into the atmosphere4 Consequently, terrestrial, aquatic, and atmospheric environments become contaminated with cadmium and remain reservoirs for human cadmium poisoning. 

We are just beginning to understand the effects that trace elements and compounds may have on man and his environment. For most of these we do not know what the toxic levels in man and animals are. Not only are some very dangerous in very small amounts, like cadmium and mercury, but others are necessary. 

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