Complexes silver-cyano

Jones and Penneman " made an extensive infrared study of the equilibria of cyano complexes in aqueous solution. (For aqueous infrared spectroscopy, see Sec. 111-9.) Figure 111-35 shows the infrared spectra of aqueous silver cyano complexes obtained by changing the ratio of Ag to CN" ions. Table 111-35 lists the frequencies and extinction coefficients from which equilibrium constants can be calculated. Chantiy and Plane studied the same equilibria using Raman spectroscopy. 

Fig. 111-35. Infrared spectra of silver cyano complexes in aqueous solutions. ...

Sodium cyanide is used in the extraction of gold and silver from ores because of the very stable linear cyano complexes formed with these metals. The molecular bonding for silver cyano complexes is drawn as [ N=C—Ag—C=N ] and similarly for gold complexes [ N C—Au—C N ]- (King, 1994). 

Among the instrumental methods, electrogravimetry (Sec.2.3.2) can be used but the best results are obtained from the silver cyano-complex. But because of the high toxicity of cyanides, the method cannot be recommended. 

See related METAL CYANIDES (AND CYANO COMPLEXES) See other SILVER COMPOUNDS... 

Silver(m) Complexes with Alkyl, Alkynyl, and Cyano Ligands 241... 

Nitrosalicylhydrazide, 2778 Scandium 3-nitrobenzoate, 3816 Silver osmate, 0034 Thallium bromate, 0260 Thallium(I) methanediazoate, 0458 Thallium(I) 2- or 4-nitrophenoxide, 2187 Thallium acz-phenylnitromethanide, 2723 See also METAL AZIDES, METAL CYANIDES (AND CYANO COMPLEXES), /V-MKTAL DERIVATIVES... 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

The main use of NaCN is in the extraction of gold and silver from their ores by the formation of cyano complexes (Section 7-12). The ions Ag+, Hg2+, and Pb2+ give insoluble cyanides. 

The low stability of two-coordinate complexes with respect to other possible structures is well illustrated by the cyano complexes. Althot silver((> and gold( ) form discrete bislcyano) complexes, solid KCu(CN)2 possesses a chain structure in which the coordination number of the cpppertD >s 3. 

The linearity of the second cyano complex T1(CN)2 is expected, because other metal ions—e.g., copper(I), silver(I), gold(I), and mercu-ry(II)—also form linear dicyano complexes (185,204). For the T1(CN)2 complex, there is strong evidence from LAXS data for a second coordination sphere comprising approximately eight water molecules at a Tl-0" distance of 4.3 A. This can be rationalized by assuming two H2O" molecules hydrogen-bonded to each of the water molecules of the first hydration sphere of an assumed Tl(CN)2(OH2)4 complex (145). 

Silver forms cyano complexes up to Ag(CN)4 v moreover, CN can be pro to na ted to form HCN. Therefore we will consider the mass balance equations... 

Silver and gold occur native, and in sulfide, arsenide and telluride ores, e.g. argentite (Ag2S) and sylvanite ((Ag,Au)Te2). Silver is usually worked from the residues of Cu, Ni or Pb refining and, like Au, can be extracted from all its ores by reaction 22.4, the cyano complex being reduced to the metal by Zn. ... 

The product of reaction depicted by Eq. (12) was assigned as the transient cyano complex of the silver atom Ag°(CN)2 . Its absorption spectrum is characterized... 

Cyanide is determined by measuring the atomic absorption of either silver, copper, or nickel in their corresponding cyano complexes, Ag(CN)2, Cu(CN)3, and Ni(CN)4. The most sensitive of these is based on the silver complex. 

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