Zinc, Cadmium, and Mercury

A number of stannyl-zinc and -cadmium compounds have been prepared by reaction of a tin-alkali metal compound with a zinc or cadmium halide, or a tin hydride with an alkyl-zinc or -cadmium compound. The coordination of a ligand such as a triphenyl-phosphine, TMEDA, or bipyridyl, or a solvating solvent such as DME, both enhances the nucleophilicity of the alkyl group in the alkylmetallic compounds and stabilises the stannylmetallic product. Thus triphenyltin hydride reacts with diethylzinc or diethylcad-mium in pentane or benzene with separation of metallic zinc or cadmium, but with a preformed complex, or in a coordinating solvent, the distannylmetallic compound is formed (e.g. equation 19-32). 

Magnesium, Zinc, Cadmium, and Mercury. —Cocondensation of magnesium vapour with THF or hexane at -196 °C, followed by warming, gives a very reactive magnesium-solvent slurry when such a mixture reacts with bromopentafluorobenzene at — 30 °C and iodine in THF is added at — 78 °C, a 77 % yield of pentafluoroiodo-benzene is obtained. 

Earlier reference has been made to vibrational studies on Zn0-B203-V20s glasses CdMoPOe and [Mo3S7(dtp)3]4l [(Hgl3)4.K], where dtp = 

Skeletal modes have been assigned, and a normal coordinate analysis carried out, using IR and Raman data for Cd(NH3)2l2, with and D/H substitu- 

Force constant calculations have been reported for the defect chalcopyrite compounds CdAl2X4, where X = S or Se. The Cd-X stretching force constant was found to be less than that for Al-X stretching. A theoretical calculation has been made of the vibrational wavenumbers for the ordered-vacancy compound Cdl2Te4.  

IR and Raman spectra of Hg2M04, where M = Mo or W, include vHgHg at 177 (IR), 187 (Raman) cm (Mo), 171 (IR), 190 (Raman) cm (W). Assigiunents were also proposed for MOe units in the factor group C2h.  

The IR and Raman speetra of Hg(SC H2 +i)2, where n = 1-10, 12, gave the assignments to Vs and VasHgS whieh are listed in Table 18. High-pressure Raman data were reported for Hgi xTOxS erystals, at pressures up to 1.6 GPa. Vibrational speetroseopie data (IR, Raman) for (DMPP)(X)Hg(p-X)2Hg(X)(DMPP), where X = Cl, Br or I, DMPP = tris(2,6- 

Much early work on organic compounds of Ca, Sr and Ba was carried out with solutions obtained by dissolving the metals in zinc dialkyls. 

The complexes MZnEt are monomeric in benzene. In cyclopentane as solvent, Hn.m.r. spectra over a range of temperatures indicate the presence of free dialkyls and a complex CaZnEt, which is probably present as a contact ion-pair. The exchange reaction presumably occurs via an alkyl-bridged species  

Ethylzinc chloride and bromide have tetrameric structures in the crystal, which are retained in solution in benzene. In contrast solid ethylzinc iodide forms polymeric chains. In all these structures zinc is four-coordinate. In ethers RZnX are monomeric through complex formation. 

Organozinc halides are less reactive than Grignard reagents and generally have been replaced by the latter for organic syntheses. There are, however, a few 

Moseley and H.M.M. Shearer, Chem. Comm., 1966, 876.) (b) Crystal structure of methylzinc methoxide tetramer (After H.M.M. Shearer and C.B. Spencer, Chem. Comm., 1966, 194). [EtZnCl] and [EtZnBr] are similar, (c) Crystal structure of [MeZnNPh2l2- All the angles in the four-membered ring are right angles. (After N.A. Bell, H.M.M. Shearer and C.B. Spencer, Acta Cryst, 1983 C39, 1182). 

Earlier reference has been made to vibrational studies on ZnO/Mo03 on Zr02 ZnCl2 M(LH)2X2, where M = Zn, CD or Hg, X = halide, LH = 3-hydroxyimino-1 -A-phenylaminobutan-1 -one [(tren)Cu(im)Zn(tren)] , where im = imidazolate, tren = tris(2-aminomethyl)amine) and Zn(SALO), where SALO = salicylaldoxime.  

The IR and Raman spectra of Cp2Zn contain vZnCp bands at 315 and 344 

Raman spectroscopy was used to characterise pure and doped ZnO at pressures up to 11.7 GPa. Bands ascribed to Zn-Se modes were seen at 222 and 235 cm in a CdSe/ZnTe superlattice.  

Raman spectra of molten ZnBr2-MBr (where M = Li or Na) systems contained bands due to the S5unmetric stretching modes of ZnBr4 (173 cm ) and Zn2Br7 (148 cm ).  

Variable-temperature Raman spectra of aqueous solutions containing Cd(OH2)6 show vCdOe bands at 235 cm and 185 cm , assigned to Cg and t2g modes respectively. The IR spectra of cadmium(II) bis(acetylacetonate) and its bis-piperazine adduct show that vCdO decreases on the additional coordination of the V-donor. 2 

SC6H4NH2. Many of these complexes have a polymeric structure and in the cases that the metal is linearly coordinated there are several possibilities of stabilization as M- S, Hg- Hg, M- N (in heterocyclic thiolates), intramolecular NH- -S, or intermolecular CH- N interactions or ti-ti stacking. For mercury other type of neutral complexes of the form [HgR(SC6H4NH2)] 

Zinc is the active metal in the largest group of metalloproteins found in the nature. Recently a new class of zinc enzymes with a sulfur-rich environment has emerged the thiolate-alkylating enzimes, the most prominent of which is the cobalamine-independent methionine synthase. For these reasons several monothiolate zinc complexes have been prepared for the modelling of these enzymes with different N2S as (13), N20, 83, tripod 

Dinuclear complexes have been reported in which the chalcogenolates act as bridging ligands between the metal centres as in [Zn p-SSi(0 Bu)3 (acac)]2,  

SBz)i6] , and several Hg Se and Hg-Te clusters, as for example [Hg32Sei4 (SePh)36l or [HgioTe4(TePh)i2(PPh Pr2)4], or [Cd Zn5Sei3(SePh)6(thf)2 (tmda)5], which have been prepared as possible precursors of 12-16 semiconductors. Finally, heterometallic Eu/M(II) (M=Zn, Cd, Hg), Ln/Hg, and Hg/Re carbonyl cluster have also been synthesized.  

This chapter reviews the inorganic co-ordination chemistry of the Group IIB elements zinc, cadmium, and mercury from September 1973 to September 1974. As this is the first review of this particular group in this series of Reports, several references to earlier work have been included, mainly for the sake of completeness where a series of papers has been published. Where a report is concerned with the comparative chemistry of all three elements, it is discussed in the section devoted to zinc. 

A separate section, compiled by Martin Hughes of the University of Cambridge, reviews advances in the bio-inorganic chemistry of the Group IIB elements, and reflects the rapid growth of interest in this area in recent years. 

Two 67Zn (natural abundance = 4.12% / = f) n.m.r. studies have been reported.9,10 The chemical shift of 67Zn (4.81 MHz at 1.807 Tesla) in aqueous zinc chloride, bromide, and iodide solutions was found to be strongly concentration dependent, while no such dependence was noted in solutions of the perchlorate, nitrate, or sulphate. This behaviour resembles that found for analogous cadmium systems, and is attributed to the formation of mono- and poly-halogeno- complexes even at low salt concentrations. In addition, the zinc halide solutions show an anomalous shift to higher frequencies for their solutions in D20, compared with those in H20. The perchlorate, nitrate and sulphate show no solvent isotope effect. 

A dissolution mechanism for zinc, cadmium, and mercury in their molten halides has been proposed on the basis of new experimental and literature data.18 Dissolution occurs at the metal-salt phase boundary. Adsorbed M2+ cations are reduced to M+ ions which then migrate into the salt phase where M2 + dimers form. The stability of the M2 + ions was found to increase in the order Zn Cd Hg (Hg+ cannot be detected in solution). 

The stability constants in melts of NH4N03,nH20 of ZnX+, ZnX2 (n 1—3 X = Cl or Br), CdX +, CdX2 (n = 1.5-3 X = Cl or Br) and HgX+, HgX2 (n = 2.5 X = Cl or Br) have been determined.19,20 The behaviour of zinc is peculiar if the K1 and K2 values are compared with those of cadmium and mercury. The stability constants increase with temperature and the bromide is more stable than the chloride, trends which are opposite to those normally observed for the halide complexes of 

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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. 

Zinc, cadmium, and mercury are the last subgroup of the transition series. Their chemistry is very like that of the alkaline earths of Group II on the periodic chart. 

Although zinc, cadmium, and mercury are not members of the so-called main-group elements, their behavior is very similar because of their having complete d orbitals that are not normally used in bonding. By having the filled s orbital outside the closed d shell, they resemble the group IIA elements. Zinc is an essential trace element that plays a role in the function of carboxypeptidase A and carbonic anhydrase enzymes. The first of these enzymes is a catalyst for the hydrolysis of proteins, whereas the second is a catalyst for the equilibrium involving carbon dioxide and carbonate,... 

Group IIB and know that this means the group of elements zinc, cadmium and mercury, whilst Group I1A refers to the alkaline earth metals beryllium, magnesium, calcium, barium and strontium. 

ALLOYS OF BERYLLIUM, MAGNESIUM, ZINC, CADMIUM AND MERCURY Beryllium, Be magnesium, Mg zinc, Zn cadmium, Cd mercury, Hg... 

Owing to some similarities among their properties and alloying behaviour, beryllium and magnesium, metals of the 2nd group, will be presented in this chapter together with the last transition metals zinc, cadmium and mercury (see a few more remarks in 5.4). 

Zinc, cadmium and mercury are at the end of the transition series and have electron configurations ndw(n + l)s2 with filled d shells. They do not form any compound in which the d shell is other than full (unlike the metals Cu, Ag and Au of the preceding group) these metals therefore do not show the variable valence which is one of the characteristics of the transition metals. In this respect these metals are regarded as non-transition elements. They show, however, some resemblance to the d-metals for instance in their ability to form complexes (with NH3, amines, cyanide, halide ions, etc.). 

Zn(R-dtp)2 complexes have been characterized and their thermal stabilities investigated 173,184,190,297-299,301-305) Zn(R-dtp)2 compounds are thermally degraded to volatile olefins and non-volatile residues and this serves as the basis for gas chromatographic determination of the compounds 304,30s) Several papers describing pyrolyses of Zn(R-dtp>2 complexes have discussed mechanisms for formation of olefins, sulfides, and other products 173,184,190,298,299, 304) Dakternieks and Graddon i8s,283)35 mentioned earlier, have reported thermodynamic measurements for depolymerization and adduct formation reactions of zinc, cadmium and mercury R-dtp compounds. 

Electrochemical synthesis and structural characterization of zinc, cadmium, and mercury complexes of heterocyclic... 

Zinc, cadmium, and mercury. A classic of science, Sci. News Letter, 19,... 

Metals more electronegative than magnesium, like beryllium, zinc, cadmium and mercury, form useful reagents for specific purposes, but the metals themselves are not sufficiently active to form organic derivatives under normal laboratory conditions and are unwanted in the environment since they are toxic. Aluminum compounds are useful for industrial purposes, but their use in the laboratory is insignificant in comparison with Grignard reagents. 

Of the Group 12 elements, zinc, cadmium and mercury, only Hg has a water-stable -I-1 state, and all three elements have + 2 states that are water-stable. Their reduction potentials are summarized in the Latimer diagram ... 

Chlorides of iron, zinc, cadmium and mercury also behave in a similar manner. 

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