Gold -cyanide AuCN

Cyanides such as silver cyanide AgCN, copper cyanide Cu(CN)2, and gold cyanide AuCN, that are used in galvanoplastic processes, lead to pitting corrosion of aluminium due to the presence of cations of heavy metals (silver, copper, and gold). 

Gold cyanide (aurus AuCN Highly toxic LD50 values Liberates toxic HCN... 

Cyanides. Salts of the complex ion, [Au(CN)2] , can be formed directiy from gold, ie, gold dissolves ia dilute solutions of potassium cyanide ia the presence of air. Additionally, a gold anode dissolves ia a solution of potassium cyanide. The potassium salt can be isolated by evaporation of the solution and purified by recrystallization from water (177). Boiling of the complex cyanide ia hydrochloric acid results ia formation of AuCN [506-65-01]. Halogens add oxidatively to [Au(CN)2] to yield salts of [Au(CN)2X2] which are converted to the tetracyanoaurates usiag excess cyanide (178). These last can also be prepared directiy from the tetrahaloaurates. 

AuCN has a similar structure to AgCN and likewise dissolves in excess cyanide to form Au(CN)J this is important in the extraction of gold. It has been characterized as various salts (Tl, K, Bu4N, Cs) with Au-C 1.964A (Bu4N salt [91]). The thallium salt has short Au-Au (3.10A) and Au-Tl (3.50 A) interactions extended-Huckel calculations indicate the importance of relativistic effects in these covalent interactions. Isocyanides form stable complexes ... 

The low solubility of AuCN(s) is thought to be a consequence of a polymeric structure based on linear chains, —Au-CN-Au-CN—, which lie parallel to one another with a close-packed arrangement of gold atoms in which each is in contact with six nearest neighbors.36 The addition of cyanide and dissolution of [Au(CN)2] is believed to take place at the chain ends. This process is enhanced by the presence of Ag2+ or other ions such as Pb2+ (see below) normally present in the gold-bearing ores. 

It should be noted that the preparation of complexes (RNC)AuCN can be carried out via very special routes. Thus AuCN reacts with Mel to give (MeNC)AuCN. This reaction involves an interesting A-alkylation of an Au(i)-bound cyanide group.219 Other (RNG)AuGN complexes were obtained from the reaction of K[AuC14] with the isocyanide in methanol. Examples are the compounds (L)Au2(CN)2 with L = l,8-diisocyano-/>-menthane or 2,5-diisocyano-2,5-dimethyl-hexane. The reactions proceed with a dealkylation of an isocyanide in the coordination sphere of a gold(m) center to produce free cyanide (Scheme 53).201... 

Both the cyanide, [Au(CN)2] , and fulminate, [Au(CNO)2] , ions contain linear gold(I) centres.387,388 A report that KAu(CN)2(2,2 -bipyridyl) contains square planar gold(I) has been disproved the bipy ligand is not coordinated to gold and the complex contains linear [Au(CN)2J ions. 390 AuCN is polymeric with a linear (—Au—CN—) Au— chain structure.391... 

For the spheroids, we were able to obtain SERS signals of cyanide, even at concentrations of cyanide too low to show changes in the visible spectra [62]. Thus, it appears that cyanide can adsorb to the surface and yet not immediately react. This is consistent with a purported mechanism of cyanide reaction with gold, in which the adsorbed cyanide ions react to form a protective AuCN layer [62]. 

The high aspect ratio gold nanorods were not eaten from the ends by cyanide, as were their spheroidal counterparts. The topology and chemical potential of edge atoms of spheroids may not favor the formation of stable films of protective AuCN. This may be the reason for enhanced reactivity and anisotropic dissolution of spheroids. 

Gold(i) Complexes. There are several aurous complexes stable in aqueous solution, the most important ones being Au(CN)J, AuCl2 and the thiosulfate species. The cyanide complex is very stable (K — 4x 1028) and is formed when AuCN is treated with an excess of cyanide or, more usually, when gold is treated with an alkali cyanide in presence of air or hydrogen peroxide. Crystalline compounds such as K[Au(CN)2] can be obtained, and the free acid, HAu(CN)2, is isolable by evaporation of its solutions as in other free cy ano acids, a hydrogen-bonded lattice with —CN—H—N C— bonds is formed. 

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