Solvated silver ions

The perfluoroalkylsilver complexes exist in a dynamic equilibrium in solution with solvated silver ion and anionic perfluoroalkylsilver complexes such as Ag[CF(CF5) r [277] The triflnoromethylated silver complex, Ag(CF3)4 , is prepared via reaction of bis(trifIuoromethyl)cadmium with silver nitrate in acetoni trile [278]... 

Association constants for salts of copper, silver, and thallium appear to reflect solvation in a fairly simple way. For example, of the perchlorate salts, only those of the poorly solvated thallium ion show association. 

Silver-Silver Ion Electrode This is the most popular reference electrode used in non-aqueous solutions. Since Pleskov employed it in acetonitrile (AN) in 1948, it has been used in a variety of solvents. It has a structure as shown in Fig. 6.1(a) and is easy to construct. Its potential is usually reproducible within 5 mV, if it is prepared freshly using pure solvent and electrolyte. The stability of the potential, however, is not always good enough. The potential is stable in AN, because Ag+ is strongly solvated in it. In propylene carbonate (PC) and nitromethane (NM), however, Ag+ is solvated only weakly and the potential is easily influenced by the presence of trace water and other impurities. In dimethylformamide (DMF), on the other hand, Ag+ is slowly reduced to Ag°, causing a gradual potential shift to the negative direction.2) This shift can reach several tens of millivolts after a few days. 

The data obtained for [2.2.2]cryptand in acetonitrile solutions were further investigated.479,480 Silver ions are strongly solvated by acetonitrile and a competition was found to exist between complexation of the ligand and the solvent. This was claimed to be predominantly responsible for the lower stability of Ag[2.2.2]+ in acetonitrile than in water and for the rapid decrease in the stability constant at low mole fraction of acetonitrile (xMccn)> This phenomenon was then studied by determining the rate of formation and dissociation of Ag[2.2.2]+ in acetonitrile-water mixtures.481... 

Values of the stability constant of silver(I) monensin in a range of non-aqueous solvents have recently been determined (log.K, 25 °C) 494 MeOH, 8.1 0.1 propylene carbonate, 15.0 0.1 DMF, 9.94 0.05 MeCN, 8.6 0.1 DMSO, 5.37 0.05. The value of K increased by 10 orders of magnitude on going from DMSO to propylene carbonate. For the aprotic solvents, K was observed to increase in the same order in which the solvation of the free silver ion decreased. The formation rates were practically diffusion controlled ( 1010M 1 s"1) in methanol, acetonitrile and DMF. 

More difficult situations may make use of the dimethoxyethane solvate112. Occasionally chlorides in [Ru(AB)2Cl2] are not readily substituted even in alcohol-water solvents. Silver ion is then quite often useful4 to yield solvated precursors, which have been considered earlier. 

This classification has been broadened39,40 by replacing the Brpnsted acid (proton donor) with a Lewis acid (an electron acceptor) and the Brpnsted base with a Lewis base (an electron donor). (A Brpnsted acid is a Lewis acid but not necessarily vice versa.) Solvent-proton interactions are therefore included as one subdivision of this classification, but many solvation reactions of cations with solvents also will be included as reactions of Lewis acid-base systems. This approach still does not solve the problem of fitting specific solvation interactions into the classification scheme. For example, acetonitrile behaves as a good Lewis base toward silver ion, but a poor one toward hydronium ion. The broader scheme also does not specifically take into account hydrogenbonding effects in hydroxylic and other solvents, which affect both the dielectric... 

Fig. 26. Comparison between radial distribution functions for 3 M silver(I) nitrate in aqueous and in DMSO solutions. Intramolecular interactions of the solvent molecules have been removed. The derived structures for the solvated silver(I) ion in the two solvents are shown.

The reasons for preferential solvation of Ag ions by acetonitrile in acetonitrile/water mixtures and the solvation shell structure of silver ions have been discussed [251]. 

There are factors other than olefin basicity and the steric effects of substituent groups on the olefin which can affect the stability of the silver ion complex. These include the energy required to displace solvate molecules from the coordination sphere of the metal ion and the degree of association between the cations and anions, especially in concentrated solutions or in solid salts. 

X 10 , where AN, DMF, and DMSO stand for acetonitrile, dimethylformamide, and dimethyl sulfoxide. The value for yJ Ag+) about 20, and for about 250. Acetonitrile solvates many ions more weakly than does water, and their resulting high reactivity is reflected in large transfer activity coefficients. In contrast, the transfer activity coefficient for silver ions in acetonitrile is small, about 1.3 x 10. For hydrogen ions in pyridine, Mukherjee gives a value of about 1.4 x 10. Values such as these have led to useful correlations and qualitative predictions. 

Useful solvents must themselves resist oxidation or reduction, should dissolve suitable ionic solutes and nonelectrolytes, and in addition should be inexpensive and obtainable in high purity. Kratochvil indicated that the most potentially useful solvents are those that have a dielectric constant greater than about 25 and have Lewis-base properties. Some solvents meeting these criteria are acetonitrile, dimethyl-sulfoxide, dimethylformamide, dimethylacetamide, propylene carbonate, ethylene carbonate, formamide, sulfolane, and y-butyrolactone. Solvents of the Lewis-base type show specific solvation effects with many metal cations (Lewis acids). Thus acetonitrile functions as a Lewis base toward the silver ion. At the same time it reacts but little with the hydrogen ion. 

Solvation of the ions is certainly a factor in these reactions, with fluoride ion being much more strongly solvated than the other anions. However, the trend is also related to changes in the degree of interaction between the halides and the silver ions. The interactions can be expressed in terms of hard and soft acids and bases (HSAB), in which... 

J. Blumberger, L. Bernasconi, I. Tavernelli, R. Vuilleumier, and M. Sprik (2004) Electronic structure and solvation of copper and silver ions A theoretical picture of a model aqueous redox reaction. J. Am. Chem,. Soc. 126, p. 3928... 

Silver and Naphtazarin Solutions. Times up to f c. When the solution contains both naphtazarin and silver cations, the solvated electrons also react partly with silver ions shortly after the pulse (J9) ... 

Soon after absorption of the irradiation pulse by a solution containing the monovalent solvated cation M+, the population of atoms is created by the reaction depicted in Eq. (2). Formation of the atom is correlated with the decay of the solvated electron and this correlation enables determination of the rate constant of the reaction. The silver ion aqueous solution was the first system thoroughly studied by pulse radiolysis and has recently been revisited (Fig- 2). The optical absorption spectra of transient silver atoms and charged dimers produced by the reaction depicted in Eq. (10) have been observed by pulse radiolysis in various solvents, for example water (Table 1). The rate constants are generally diffusion-controlled, as are those for the corresponding reactions for formation of Tl and... 

It is interesting to note that the value of log (for the solvated AgCl species) is larger in DMSO than in water indicating that the silver ion is more strongly solvated in the non-aqueous solvent. - In addition, the magnitude of K 2 for the reaction... 

The composition of the DMSO solvate can be interpreted more unambiguously in the AgC104-CH30H-DMS0 system [Ro 76]. From the dependence of the chemical shift on the AgC104 concentration and on the composition of the mixed solvent, it could be established that the silver ion coordinates four DMSO molecules at most. 

From the above and similar investigations [Mo 71, Be 73], it could be seen that, in various binary solvent mixtures containing water, acetonitrile, methanol and dimethyl sulphoxide, the solvating effects of the individual components are generally proportional to the effects displayed by the pure solvents. An exception is the H2O-DMSO mixture, in which the silver ion occurs only in the forms of its pure aquo complex and its pure DMSO complex. 

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