The Coinage Metals

The oxide is soluble in ammonia to give the complex [AglNHjlj] (linear). On heating, silver(I) oxide loses oxygen to give the metal (all the coinage metal oxides have low thermal stability and this falls in the order Cu > Ag > Au). 

Ruthenium and osmium are generally found in the metallic state along with the other platinum metals and the coinage metals. The major source of the platinum metals are the nickel-copper sulfide ores found in South Africa and Sudbury (Canada), and in the river sands of the Urals in Russia. They are rare elements, ruthenium particularly so, their estimated abundances in the earth s crustal rocks being but O.OOOl (Ru) and 0.005 (Os) ppm. However, as in Group 7, there is a marked contrast between the abundances of the two heavier elements and that of the first. 

Collectively known as the coinage metals because of their former usage, these elements were almost certainly the first three metals known to man. All of them occur in the elemental, or native , form and must have been used as primitive money long before the introduction of gold coins in Egypt around 3400 BC. 

The fee lattice of the coinage metals has 1 valency electron per atom (d °s ). Admixture with metals further to the right of the periodic table (e.g. Zn) increases the electron concentration in the primary alloy ( -phase) which can be described as an fee solid solution... 

The selenides and tellurides of the coinage metals are all metallic and some, such as CuSe2, CuTc2, AgTe. 3 and Au3Tc5 are superconductors at low temperature (as also are CuS and CUS2). 

Like all the coinage metals, copper forms compounds with oxidation number + 1. However, in water, copper(I) salts disproportionate into metallic copper and copper(II) ions. The latter exist as pale blue [Cu(H20)6]2+ ions in water. 

C20-0067. Identify the coinage metals and describe some of their applications. C20-0068. Identify the platinum metals and describe some of their applications. C20-0069. What features of titanium account for its use as an engineering metal C20-0070. Explain why titanium(IV) oxide is used extensively as a white pigment. 

Kello, V., Urban, M. and Sadlej, A.J. (1996) Electric dipole polarizabilities of negative ions of the coinage metal atoms. Chemical Physics Letters, 253, 383-389. 

Saue, T. and Jensen, H.J.Aa. (2003) Linear response at the 4-component relativistic level Application to the frequency-dependent dipole polarizabilities of the coinage metal dimers. Journal of Chemical Physics, 118, 522-536. 

Pempointner, M., Schwerdtfeger, P. and Hess, B.A. (2000) Accurate electric field gradients for the coinage metal chlorides using the PCNQM method. International Journal of Quantum Chemistry, 76, 371-384. 

Kariis, H., Westermark, G., Persson, I. and Liedberg, B. (1998) Infrared Spectroscopic and Temperature-Programmed Desorption Studies of Dimethylphenylphosphine Adsorbed on the Coinage Metals. Langmuir, 14, 2736-2743. 

The reaction was studied for all coinage metal nanoparticles. In the case of GMEs the rate follows zero-order kinetics with IT for all the coinage metal cases. The observed IT for the Cu catalyzed reaction was maximum but its rate of reduction was found to be minimum. Just the reverse was the case for Au and an intermediate value was obtained for the Ag catalyzed reaction (Figure 7). The adsorption of substrates is driven by chemical interaction between the particle surface and the substrates. Here phe-nolate ions get adsorbed onto the particle surface when present in the aqueous medium. This caused a blue shift of the plasmon band. A strong nucleophile such as NaBH4, because of its diffusive nature and high electron injection capability, transfers electrons to the substrate via metal particles. This helps to overcome the kinetic barrier of the reaction. 

The reddish metal was already known in prehistoric times. It occasionally occurs as a native metal, but mostly in conspicuous green ores, from which it is extracted relatively easily. It is convenient to work, but not very hard. Not very optimal as a tool ("Otzi the Iceman" had a copper axe with him). Only through the addition of tin is the more useful bronze obtained. Its zinc alloy is the versatile and widely used brass. Copper is one of the coinage metals. Water pipes are commonly made of copper. Its very good thermal and electrical conductivity is commonly exploited (cable ), as well as its durability (roofs, gutters), as the verdigris (basic copper carbonate) protects the metal. Cu phthalocyanines are the most beautiful blue pigments. Seems to be essential to all life as a trace element. In some molluscs, Cu replaces Fe in the heme complex. A 70-kg human contains 72 mg. 

Compositional variations in sequential coin issues, say, from year to year, may reflect differences in the source of the ores from which the coinage metals or alloys were extracted. 

Ans. (a) Pb4 + and Pb2+. (The maximum oxidation state of a group IV element and the state 2 less than the maximum.) (b) Tl3+ and Tl+. (The maximum oxidation state of a group III element and the state 2 less than the maximum.) (c) Sn4+ and Sn2+. (The maximum oxidation state of a group IV element and the state 2 less than the maximum.) (d) Cu+ and Cu2 +. (The maximum oxidation state for the coinage metals is greater than the group number.)... 

The coinage metals are malleable and ductile, and are very good conductors of electricity. They are rather unreactive, and the ways they combine are simpler than those of the other transition elements. They usually combine by losing one, two, or three electrons. 

Laibinis PE, Whitesides GM, Allara DL, Tao Y-T, Parikh AN, Nuzzo RG (1991) Comparison of the structures and wetting properties of self-assembled monolayers of n-alkanethiols on the coinage metal surfaces, copper, silver, and gold. J Am Chem Soc 113 7152-7167... 

A recent study (1) has demonstrated that the electrochemical oxidation of hydroxide ion yields hydroxyl radical ( OH) and its anion (O"-). These species in turn are stabilized at glassy carbon electrodes by transition-metal ions via the formation of metal-oxygen covalent bonds (unpaired d electron with unpaired p electron of -OH and O- ). The coinage metals (Cu, Ag, and Au), which are used as oxygen activation catalysts for several industrial processes (e.g., Ag/02 for production of ethylene oxide) (2-10), have an unpaired electron (d10s1 or d9s2 valence-... 

The final step may be slow and represent the path for passivation of the surfaces of the coinage metals. 

It was found that the electrocatalytic activity strongly depends on the nature of the electrode it decreases in the order Rh > Ru > Ir > Pd and Pt for the transition-metal electrodes and in the order Cu > Ag > Au for the coinage metals. It was concluded that the rate-determining step on Ru, Rh, Ir, Pt, Cu, and Ag is the reduction of nitrate to nitrite. It was assumed that chemisorbed nitric oxide is the key surface intermediate in the nitrate reduction. It was suggested that ammonia and hydroxylamine are the main products on transition-metal electrodes. This is in agreement with the known mechanism for NO reduction, which forms N2O or N2 only if NO is present in the solution. On Cu the production of gaseous NO was found, which was explained by the weaker binding of NO to Cu as compared to the transition metals. 

The coinage metals, Cu, Ag, Au, with atomic structures nd n + l)s, can be viewed as a bridge between the simple s-only alkali metals and the more complicated transition metals. There exist a considerable number of... 

Most commonly, metal ions M2+ and M3+ (M = a first transition series metal), Li+, Na+, Mg2+, Al3+, Ga3+, In3+, Tl3+, and Sn2+ form octahedral six-coordinate complexes. Linear two coordination is associated with univalent ions of the coinage metal (Cu, Ag, Au), as in Ag(NH3)2+ or AuCL Three and five coordination are not frequently encountered, since close-packing considerations tell us that tetrahedral or octahedral complex formation will normally be favored over five coordination, while three coordination requires an extraordinarily small radius ratio (Section 4.5). Coordination numbers higher than six are found among the larger transition metal ions [i.e., those at the left of the second and third transition series, as exemplified by TaFy2- and Mo(CN)g4 ] and in the lanthanides and actinides [e.g., Nd(H20)93+ as well as UC Fs3- which contains the linear uranyl unit 0=U=02+ and five fluoride ligands coordinated around the uranium(VI) in an equatorial plane]. For most of the metal complexes discussed in this book a coordination number of six may be assumed. 

Of the coinage metals, finely divided copper shows evidence of strong rehybridization of adsorbed ethyne, such as occurs with transition metals Ni, Pd, Pt, and Rh, which have unfilled d orbitals. On the other hand, SER spectra from ethyne on cold-deposited silver at low temperatures show only moderately perturbed 7T-bonded species. There is SERS evidence of polymerization to long-chain polyenes on silver and gold electrodes at room temperature. 

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