Ammine-silver complexes

Most systems that have been studied possess a spreading that is wider than the statistical one or, in other words, show a positive residual effect. It is therefore noteworthy that the silver(I)-ammine system (4), which, in regard to coordination numbers (77) and characterizing d configuration, is analogous to the copper(I) system, has a negative residual ect. This unexpectedly low occurrence of the silver(I)-monoammine complex - only 20% at the maximum — is not understood. However, in view of the very small standard free energy differences that we are concerned with, it will probably be a while before we come to understand the subtle difference between copper(I) and silver(I). 

Ammonia forms a great variety of addition or coordination compounds (qv), also called ammoniates, ia analogy with hydrates. Thus CaCl2 bNH and CuSO TNH are comparable to CaCl2 6H20 and CuSO 4H20, respectively, and, when regarded as coordination compounds, are called ammines and written as complexes, eg, [Cu(NH2)4]S04. The solubiHty ia water of such compounds is often quite different from the solubiHty of the parent salts. For example, silver chloride, AgQ., is almost iasoluble ia water, whereas [Ag(NH2)2]Cl is readily soluble. Thus silver chloride dissolves ia aqueous ammonia. Similar reactions take place with other water iasoluble silver and copper salts. Many ammines can be obtained ia a crystalline form, particularly those of cobalt, chromium, and platinum. 

Hydrate Isomerism.—As its name implies, this depends on the position of water in the molecule, just as in the case of the acido compounds. If two or more molecules of water are present in a molecule of ammine, the water may be present within the co-ordination complex or outside of it. For instance, the compound Cr en2.(H20)2.Br3 exists in isomeric forms. It may have all the water within the complex, in which case the formula will be [Cr en2(H20)2]Br3. In solution the whole of the bromine is precipitated by silver nitrate. On the other hand, the compound may have one molecule of water in the complex and the other outside, in which case the formula is [Cr en2(IT20)Br]Br2.H20, and only two-thirds of the bromine are precipitated by silver nitrate. Another example of this kind occurs in the cobalt series chloro-aquo-tetrammino-cobaltic chloride, [Co(NTI3)4Cl.H20]Cl2, is violet in colour, and is isomeric with dichloro-tetrammino-cobaltie chloride monohydrate, [Co(N1I3)4CI2]C1.H20, which is green. 

Gold has a more marked tendency to form complex salts than either copper or silver, but the ammines of gold arc somewhat unstable. Gold forms two series of salts where the metal is monovalent or divalent respectively from both series of salts ammines have been obtained. 

The resolution was carried out by means of d-bromo-camphor-sulphonie acid. The salts of the bromo-series are more easily resolved on account of the great difference between the isomeric d-bromo-camphor sulphonates. In both series the d-bromo-eamphor sulphonate of the d-isomer is more sparingly soluble. These active compounds are very stable, and aqueous solutions of the bromides of the bromo-ammine series may be kept for a considerable time at ordinary temperatures, and even on heating to boiling racemisation does not occur. If the bromine in the complex be removed by means of silver nitrate activity... 

Controlled growth of previously deposited very small silver particles can also be performed. The procedure involves to establish first the minimum temperature at which reduction of the metal proceeds in the bulk of the solution. With the reduction of silver ammine complexes by formaldehyde, the temperature to effect reduction in the bulk of the liquid is about 310K. It has been found that metallic silver particles catalyze the reduction of the silver ammine complexes. By suspension of a silica support covered with small silver particles in a solution of Ag(NH3)7 cooling the suspension to 273 K and subsequently injection of formaldehyde, controlled growth of the silver particles can be achieved. It is interesting that the silver particles... 

Tannic acid-silver nitrate test The basis of this test is the reducing action of tannic acid (a glucoside of digallic acid) upon the silver ammine complex [Ag(NH3)2]+ to yield black silver it therefore precipitates silver in the presence of ammonia but not from a slightly acid silver nitrate solution. 

Determination of Instability Constant.—Two methods have been mainly used for determining the instability constants of complex ions one involves the measurement of the e.m.f. s of suitable cells, which will be described in Chap. VII, and the other depends on solubility studies. The latter may be illustrated by reference to the silver-ammonia (argent-ammine) complex ion. If the formula of the complex is Agm(NH8)n , the... 

As an example of the first kind of outer-sphere complex formation, Werner (44) studied the interaction of thiocyanato complexes of cobalt (Ill)ammines with silver ions. In these complexes nitrogen is bound to the metal, and the sulfur atom in the thiocyanate group is free to complex... 

A potentiometric titration will be run using a solution of your cobalt(III) complex and aqueous silver nitrate (AgN03) as a titrant. AgN03, which is soluble in aqueous solution, undergoes a double displacement reaction with the cobalt ammine complex according to equation (2.10). 

Silver (Ag, at. mass 107.87) occurs in its compounds in the (I)- oxidation state. So far, silver(II) is only of limited value in spectrophotometry. Silver(I) -sulphide and -halides are sparingly soluble. Ammine, cyanide, and thiosulphate complexes of silver are formed. In the presence of excess of Cf or SCN , traces of silver form soluble complexes. 

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