Gold compounds Subject

None of the oxidation states occurring in gold compounds can really be said to be thermodynamically stable. Gold (II) and gdd(l) are subject to disproportionation. The reduction potential of gdd(IIl) to gdd(l) is marginally above that necessary to oxidize water, but the presence of complexing agents can stabilize +1 and +3. with the latter usually being the more stable. 

Corrosion is the deterioration of a material due to interaction with its environment It is the process in which metallic atoms leave the metal or form compounds in the presence of water and gases. Metal atoms are removed from a structural element until it fails, or oxides build up inside a pipe until it is plugged. All metals and alloys are subject to corrosion. Even the noble metals, such as gold, are subject to corrosive attack in some environments. 

Two forms of gold provide medical treatments. The radioactive isotope Au-198, with a short half-life of 2.7 days, is used to treat cancer and is produced by subjecting pure gold to neutrons within a nuclear reactor. A gold salt, a solution called sodium thiosulfate (AuNa O Cl ), is injected as an internal treatment for rheumatoid arthritis. However, since gold and some of its compounds are toxic when ingested, this treatment may cause complications such as skin rashes and kidney failure. It is a less popular treatment, particularly with the development of newer and more effective medications. 

Thanks to the extensive literature on Aujj and the related smaller gold cluster compounds, plus some new results and reanalysis of older results to be presented here, it is now possible to paint a fairly consistent physical picture of the AU55 cluster system. To this end, the results of several microscopic techniques, such as Extended X-ray Absorption Fine Structure (EXAFS) [39,40,41], Mossbauer Effect Spectroscopy (MES) [24, 25, 42,43,44,45,46], Secondary Ion Mass Spectrometry (SIMS) [35, 36], Photoemission Spectroscopy (XPS and UPS) [47,48,49], nuclear magnetic resonance (NMR) [29, 50, 51], and electron spin resonance (ESR) [17, 52, 53, 54] will be combined with the results of several macroscopic techniques, such as Specific Heat (Cv) [25, 54, 55, 56,49], Differential Scanning Calorimetry (DSC) [57], Thermo-gravimetric Analysis (TGA) [58], UV-visible absorption spectroscopy [40, 57,17, 59, 60], AC and DC Electrical Conductivity [29,61,62, 63,30] and Magnetic Susceptibility [64, 53]. This is the first metal cluster system that has been subjected to such a comprehensive examination. 

The area of organogold chemistry has also blossomed in the past ten years. In a 1926 review article (2) it was stated that Gold has no affinity for carbon. Complex organic compounds of gold in which the gold is directly attached to carbon are incapable of existence, or at least cannot be isolated. In fact, only a few workers were active in this field for many years, and the past decade has produced about 75% of the presently existing contributions to the subject. 

Extraction is rapid compared to that by cyanidation, and the gold surface is not subject to the passivation observed in alkaline cyanide solutions. At present, the main disadvantage of the process is the high cost of the reagents, which is compounded by the instability of thiourea with respect to hydrolysis and to oxidation under the conditions of the leach. 

The authors used silver salts since gold salts catalyzed the reaction with R=H (giving oxazole 34, Scheme 5.16) but not with R=Me. Moreover, only traces of the desired furopyrrolidinone were formed with the use of a cationic gold species activated with silver additives. Therefore, silver traces were thought to be the active reagent. Indeed, on activation of compound 33 mediated by AgN03 in the presence of sodium acetate (Scheme 5.16), the enol moiety V can then accomplish a nucleophilic attack to produce the pyrrolidinone W and after protonolysis give compound X. Pyrrolidinone Y (the enol version of X) can, in turn, be subject to an oxidative cyclization to yield the furopyrrolidinone 35. Two equivalents of silver salts are needed for the activation step and the oxidative cyclization. 

Silver is another native metal found in museum collections in a variety of forms. Chemically, silver differs gready from gold in that it is highly reactive. Silver occurs in its native state, but is more stable in compounds with other elements. The black tarnish so common on silver items is silver sulfide. Silver objects that have been buried for any length of time may be completely altered, particularly if water is present. When the alteration that begins as tarnish is complete, and all native silver has been combined with other elements, a worked piece will usually lose its integrity and disintegrate. If silver is subjected to moisture in the presence of the element chlorine, as it would in seawater or brackish water, horn silver or silver chloride may develop. 

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