Gold-silver compounds

Although there is an analogy in many aspects between the structural chemistry of heterometallic Au-Ag and Au-Cu compounds, the interest shown in recent years has resulted in a considerable increase in the structural diversity for the gold-silver species resulting from the different strategies used to obtain compounds with a pre-established design, but also due to many unexpected compounds. 

The phosphorus ylide complex [(Ph3PCH2)2Au]2Ag2(C104)4 445 also contains Au-Ag bonds [(2.783(2)/2.760(2) A] unsupported by any covalent bridge within a Au2Ag2 ring, but each silver atom is further bonded to two oxygen atoms from two 

A further few ionic compounds based on unsupported heterometallic interactions between metal centers from the anion and the cation were reported only recently [604—606]. Thus, treatment of [Ag(Tab)2](PF6) with K[Au(CN)2] generated the complex [ (Tab)2Ag Au(CN)2 ]2 446 [605]. In the solid state [Ag(Tab)2]+ cations and [Au(CN)2] anions are held together via ionic interactions [Au-Ag 2.9598(7)/2.9185 

Trimetallic clusters with a tetrahedral AuRe2Ag skeleton [194, 201, 202] were also reported, for example (Ph3P)Au (Ph3P)Ag Rc2(p.-PCy2)(CO)7(C = CPh) 168 [Au-Ag 2.756(1) A] [201]. 

The unusual trimetallic derivative, [(dppe)Au2]2Ag4[Fe(CO)4]4 281 (see also Section 4.3.5), exhibits a metal atom framework described as a two-dimensional triangulated twisted ribbon, with gold atoms of (dppe)Au2 units connected to the same silver atom [Au-Ag 2.767(2)-2.824(3) A] [401]. 

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The pyrometaHurgical processes, ie, furnace-kettle refining, are based on (/) the higher oxidation potentials of the impurities such as antimony, arsenic, and tin, ia comparison to that of lead and (2) the formation of iasoluble iatermetaUic compounds by reaction of metallic reagents such as 2iac with the impurities, gold, silver and copper, and calcium and magnesium with bismuth (Fig. 12). 

Selenium occurs in the slimes as intermetallic compounds such as copper silver selenide [12040-91 -4], CuAgSe disilver selenide [1302-09-6], Ag2Se and Cu2 Se [20405-64-5], where x < 1. The primary purpose of slimes treatment is the recovery of the precious metals gold, silver, platinum, palladium, and rhodium. The recovery of selenium is a secondary concern. Because of the complexity and variabiUty of slimes composition throughout the world, a number of processes have been developed to recover both the precious metals and selenium. More recently, the emphasis has switched to the development of processes which result in early recovery of the higher value precious metals. Selenium and tellurium are released in the later stages. Processes in use at the primary copper refineries are described in detail elsewhere (25—44). 

Silver, a white, lustrous metal, slightly less malleable and ductile than gold (see Gold and gold compounds), has high thermal and electrical conductivity (see SiLVERAND SILVER alloys). Most silver compounds are made from silver nitrate [7761-88-8], AgNO, which is prepared from silver metal. 

In the Parkes desilvering process, 1—2% zinc is added to molten lead where it reacts with any gold, silver, and copper to form intermetaUic compounds which float as cmsts or dross that is skimmed (see Lead and lead alloys). 

The limited anodic potential range of mercury electrodes has precluded their utility for monitoring oxidizable compounds. Accordingly, solid electrodes with extended anodic potential windows have attracted considerable analytical interest. Of the many different solid materials that can be used as working electrodes, the most often used are carbon, platinum, and gold. Silver, nickel, and copper can also be used for specific applications. A monograph by Adams (17) is highly recommended for a detailed description of solid-electrode electrochemistry. 

Figure4.11 Comparison of experimental dissociation energies of gold intermetallic compounds with those of copper and silver from mass spectroscopic measurements by Cingerich and coworkers [18, 159, 173, 176] arranged in group order according to the periodic table.

The common oxidation states for gold in the dithiocarbamato complexes are + 1 and + 3. Like for the silver compounds the oxidation state + 2 is observed in diluted liquid and solid solutions only. 

Carbene complexes have also been prepared by transmetallation reactions. Lithiated azoles react with gold chloride compounds and after protonation or alkylation the corresponding dihydro-azol-ylidene compounds, e.g., (381) or (382), are obtained.22 9-2264 Silver salts of benz-imidazol have also been used to obtain carbene derivatives.2265 Mononuclear gold(I) carbene complexes also form when trimeric gold(I) imidazolyl reacts with ethyl chlorocarbonate or ethyl idodate.2266,2267 The treatment of gold halide complexes with 2-lithiated pyridine followed by protonation or alkylation also yields carbene complexes such as (383).2268 Some of these carbene complexes show luminescent properties.2269-2271... 

Siloxane compounds, in vitreous silica manufacture, 22 414 Siloxane materials, 20 240 Siloxane oligomers, in silicone polymerization, 22 555-556 Siloxanols, silylation and, 22 703 Silsesquioxane hybrids, 13 549 Silsesquioxanes, 15 188, 22 589-590 SilvaGas process, 3 696, 697 Silver (Ag), 22 636-667. See also Silver compounds. See Ag entries Argentothiosulfate complexes Batch desilverizing Lead-silver alloys Palladium-silver alloy membranes analytical methods for, 22 650-651 applications of, 22 636-637, 657-662 as bactericide, 22 656, 657, 660 barium alloys with, 3 344 in bimetallic monetary system, 22 647-648 in cast dental gold alloys, 8 307t coke formation on, 5 266 colloidal precipitation color, 7 343t colloidal suspensions, 7 275 color, 7 334, 335... 

Alloys with Copper compounds Silver compounds Gold compounds... 

Uses. The unalloyed metal cannot be directly used owing to its bad mechanical properties and its high oxidability. Several thallium alloys are used as semiconductors or ceramic compounds it may be used as additive to gold, silver or copper contacts in the electronic industries. Thallium is dangerously toxic. 

Although the description fulminating is not used and thus confusion with the fulminate not caused, mercury also forms explosive compounds of similar nature. The nitride (ibid.) is the most common and can be formed from the metal and ammonia in some circumstances, causing accidents where mercury manometers are used with ammonia. Halo-hydroxy- and oxy-nitrides can also be involved [3], See METAL FULMINATES, GOLD COMPOUNDS, A-METAL DERIVATIVES, PRECIOUS METAL DERIVATIVES, SILVER COMPOUNDS... 

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