Silver, and Gold

McConnell and Weaver, using the nmr line width method, have obtained a value for the observed rate coefficient, for the reaction in 12 M hydrochloric acid media, of 5 x 10 l.mole . sec. The width of the Cu NMR line from copper(I) ( 1 M) was observed in the presence of copper(II) (10 to 10 M). In this media the exchanging species are probably CuCl4 and CuCls . Optical interaction effects have been observed in mixtures of Cu(I) and Cu(II) in chloride media.  

Gordon and Wahl have used the radioisotope °Ag as a tracer for a study of the exchange of silver between Ag(II) and Ag(I) in acidic media. The precipitation of Ag(phen)2(C104)2, brought about by the addition of o-phenanthroline, formed the basis of the separation method. The experimental data were obtained using a 

Variation of the hydrogen-ion concentration, over the range 5.87 to 3.94 M at a constant ionic strength of 5.87 M (CIO4 ), led to the conclusion that the full rate law was 

Previously, Bruno and Santoro had found complete exchange occurred between the ions Ag(dipy)2 or Ag(phen)2 and Ag, in nitric acid solution, within the separation time. 

Copper, Silver, and Gold.—The photoisomerization reaction (80) is catalysed by Cu(OAc)2, Cu(acac)2, or CuCl2.288 Cu(ClC 4)2 promotes the photocyclodimerization of -vinylcarbazole (VCZ).290 The process involves initial electron-transfer from the singlet or triplet state of VCZ to Cu11, giving VCZ+ and Cu1. In contrast to its thermal decomposition, irradiation of Ag(BunXPBuns) causes cleavage of the Ag—C bond and the liberation of butyl radicals.291 

Copper, Silver, and Gold.—Use of the pentafluorophenylcopper-dioxan complex as a means of providing copper coatings on a range of technological materials has been patented.  

The most interesting complexes are the bidentate and tetrahedral complexes. In P388, maximal ILS values of 93% for [ AuCl 2(dppe)] and 86% for [Au(dppe)]Cl were obtained [95]. The nature of the tetrahedral 

As stated, the tetrahedral complexes are the most active, and the conversion of the bis(gold) species to such moieties has in fact been observed in plasma  

Some dissociation of free phosphine is also observed in solution [97]. A relevant finding in this work is that the free phosphine is also active [95] (originally reported in 1966 [110]), and the implication is that the gold complex serves as a releasing mechanism for the cytotoxic ligand. Since copper salts potentiate the activity of free phosphine [111] there is a possibility of in vivo phosphine release followed by copper activation — similar in concept to the possible antitumour mechanisms of 1,10-phenan-throline and the thiosemicarbazones. In pursuit of this line, Cu(II) was shown to displace dppe from [Au(dppe)2]Cl [112] to give a Cu(I) complex. Further synthesis and testing of copper-diphosphine complexes struc- 

A FAB-MS study has been conducted on carbene complexes Au[C(Y)NHAt]2 X and Au[C(Y)NHAr]2l2 +X-(Y=OEtorNHAr Ar=/7-MeC6H4 XCIO4 or BF4). 

The synthesis, Raman, IR and NMR spectra of [Au(CO)2][Sb2Fu] (26), stable at 130°C, have been reported. The near absence of Au- CsO tc back-donation in (26) results in strong C-0 bonds and weak Au-C bonds [v(CO) = 2254 and 2217 cm ]. 

Syntheses, IR and NMR spectra and methylation reactions have been rqwrted for 

Thermolysis of c -[Me2Au(C02Me)PPh3], obtained from [Mei2Au(OMe)PPh3] and CO, 

Walborsky, J. Oilman, C. Hamdruchi and M. Topolski, Tetrahedron Lett., 1972, 33,761. 

The three metals copper, silver, and gold comprise group Ib of the periodic table. These metals all form compounds representing oxidation state +1, as do the alkali metals, but aside from this they show very little similarity in properties to the alkali metals. The alkali metajs are ery soft and light, and very reactive chemically, whereas the metals of ihe copper group are much harder and heavier and are ratlier inert, sufficiently so to occur in the free state in nature and to be easily obtainable by reducing their compounds, sometimes simply by heating. 

The oxidation states of copper, sih er, and gold represented in their important compounds are shown in tlie diagram below. 

The principal compounds of copper are the cupric compounds, containing bipositive copper. The cupric ioriy Cu++ (or Cu (H20)4++), occurs in many salts. The cuprous ion, Cu , is unstable, and the cuprous c6 Aii)07uuls, except the very insoluble ones, are easily oxidized. 

The aurous ion, Au, and the auric ion, Au+ + +, are themselves unstable in aqueous solution. The stable aurous and auric compounds contain covalent bonds, as in the complex ions AuCl2 and AUCI4 . 

Silver is a soft, white metal, somewhat denser than copper, and with a lower melting point. It is used in coinage, jewelry, and table ware, and as a filling for teeth. 

For many years, the chemistry of silver and gold was believed to be more similar than is now known to be the case [1-10]. In the Cu-Ag-Au triad, the stability of oxidation states does not follow the usual trend of increasingly stable high oxidation state on descending the group for copper, the +2 state is the most important, for silver it is the +1 state and, though oxidation states between -1 and +7 are claimed, for gold it is the +1 and +3 states that dominate its chemistry. The types of compound are summarized in Table 4.1. 

All three M+ ions are known to form compounds with the unusual digonal linear coordination (see also section 4.9.7), though this is most common for gold. As a result, complexes R3PMX of copper and silver are normally di-and tetranuclear species with 3- or 4-coordinate metals, while the gold analogues are 2-coordinate monomers. This is the reverse of what would be expected on steric grounds [13, 14], 

Among other contributions concerning more complicated adsorbates are those dealing with the species formed on Ag during ethylene and propylene oxidation. 

Chesters, J. Pritchard and M. L. Sims, in Adsorption-Desorption Phenomena ed. F. Ricca, Academic Press, London, 1972, p. 277. 

One of the earliest applications of radioactive tracer techniques to surface investigations is that of Paneth and Vorwerk/ who used the Pb isotope, thorium B, to determine the surface area of powdered PbS04 by exchange between the surface Pb ions of the solid and the radioactive Pb in solution. Since then a vast number of studies of catalytic systems involving the use of radioisotopes have been reported. As the earlier literature has been extensively reviewed by Campbell and Thomson, the present Report is mainly concerned with the literature published between 1970 and mid-1982, particular emphasis being placed on new developments in experimental methods. 

About the only catalytic use for silver is in the conversion of ethylene to ethylene oxide by the action of oxygen.42 This reaction is very specific. Other alkenes are oxidized to CO2 and H2O with no epoxide formation observed. Gold is generally inactive as a catalyst for most reactions but it has found some use in catalytic oxidations. 43 

Substances that are deliberately or inadvertently added to a metal catalyst may have an influence on the activity of the catalyst and the selectivity of the reaction. These changes are brought about when the added material, a modifier, is adsorbed on the surface of the catalyst. Catalyst modification is brought about because the 

The nature of the metal and the conditions used for the reaction can also have an effect on this competitive adsorption. In addition, since these strongly adsorbed species seem to prefer to adsorb initially on the more coordinately unsaturated surface sites, the extent of inhibition can also depend on the morphology of the catalyst surface. -  

Catalyst poisons and inhibitors are usually added inadvertently to the reaction mixture by the use of impure solvents or substrates. Promoters, however, are generally added deliberately to enhance catalyst activity and/or reaction selectivity. 

The simple argentic ion has been produced in concentrated nitric acid solution, but apart from the fluoride, Agp2, compounds of Ag(ii) can be prepared only in the 

The simplest possibilities are the formation of two collinear (sp) or four tetrahedral (sp ) bonds. In addition, Cu(i) and Ag(i) form three bonds in a number of crystals, and we shall give examples of this bond arrangement after dealing with the two simpler ones. 

For Au(i) two is the preferred coordination number. AuCN and K[Au(CN)2] are isostructural with the Ag compounds only approximate bond lengths were determined. The most stable amino derivatives of AuCl are H3N. AuCl and (H3N-AU—NH3)C1, and whereas with ligands such as thioaceta-mide Cu and Ag form salts of type (d), Au forms only the rather unstable salt (e). 

With trialkyl phosphines and arsines cuprous and argentous halides form the tetrameric molecules [R3P(As). Cu(Ag)X] 4, but Au forms only R3P(As). AuX. In addition to the cases already noted, X-ray studies have demonstrated the formation of two collinear bonds by Au(i) in Aul, which consists of chains of the type 

No example of Au(i) forming four tetrahedral bonds has yet been established by a structural study, but tetrahedral bonds are formed in numerous compounds of Cu(i) and Ag(l), the simplest examples being the cuprous halides and Agl with the zinc-blende structure (p. 349). 

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Al-Obaidi A H R, Rigby S J, Hegarty J N M, Bell S E J and McGarvey J J 1996 Direct formation of silver and gold metal liquid-like films (MELLFS) from thiols and sols without organic solvents SERS and AFM studies ICORS 96 XVth Int. Conf on Raman Spectroscopy ed S A Asher and P B Stein (New York Wiley) pp 590-1... 

The most important ores are bismuthinite or bismuth glance and bismite. Peru, Japan, Mexico, Bolivia, and Canada are major bismuth producers. Much of the bismuth produced in the U.S. is obtained as a by-product in refining lead, copper, tin, silver, and gold ores. 

Epoxies are the most commonly used adhesives (qv). Silver and gold are sometimes added to an epoxy to improve its thermal conductivity. Polyimide, also used as an adhesive, has low shrinkage as well as low viscosity and can be cured at 180°C its primary drawback is a tendency to absorb water, as much as 6% by weight. 

Platinum was found in conjunction with gold after the Spanish conquest of South America. It was referred to as platina, or Htde silver. It was regarded as an unwanted impurity in the silver and gold, and was often discarded. However, scientific interest in platinum gradually grew and in 1741 the first samples of New World platinum were brought to England for scientific examination. 

Organ oselenium compounds, such as phosphine selenides, are being evaluated in solvent extraction systems for silver and gold (63). Also, potential pharmaceuticals containing selenium have been prepared (64). 

Refining. The alloy of bismuth and lead from the separation procedures is treated with molten caustic soda to remove traces of such acidic elements as arsenic and teUutium (4). It is then subjected to the Parkes desilverization process to remove the silver and gold present. This process is also used to remove these elements from lead. 

Copper, the first element of Group 11 (IB) of the Periodic Table, is immediately above silver and gold. It is classed with silver and gold as a noble metal and can be found in nature in the elemental form. Copper occurs as two natural isotopes, Cu and Cu (1). 

Table 4. Properties of Pure Copper, Silver, and Gold ...

The thermodynamics of copper smelting are discussed ia References 17 and 18. Silver and gold are quantitatively recovered with the copper throughout the smelting operations rather than being lost with the slag. 

Examples of plating solutions having good throwing power include cyanide plating baths such as copper, zinc, cadmium, silver, and gold, and noncyanide alkaline zinc baths. Examples of poorer throwing power baths are acid baths such as copper, nickel, zinc, and hexavalent chromium. 

Mercury is used in the manufacture of thermometers, barometers and switchgear, and in the production of amalgams with copper, tin, silver and gold, and of solders. A major use in the chemical industry is in the production of a host of mercury compounds and in mercury cells for the generation of chlorine. Mercury has a significant vapour pressure at ambient temperature and is a cumulative poison. 

Table 28.1 Some properties of the elements copper, silver and gold...

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