Silver cryptand stability

The Ag+ ion is labile. Even with cryptands, which react sluggishly with most labile metal ions, Ag reacts with a rate constant around 10 M s (in dmso). The higher stability of Ag(I) complexes compared with those of the main groups I and II resides in much reduced dissociation rate constants. Dissociation tends to control the stability of most metal cryp-tand complexes. Silver(I) is a useful electron mediator for redox reactions since Ag(I) and Ag(II) are relatively rapid reducers and oxidizers, respectively. Silver(I) thus promotes oxidation by sluggish, if strong, oxidants and catalyses a number of oxidations by S20 in which the rate-determining step is... 

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... 

The mechanism of 1 1 complex formation between palladium(II) and catechol and 4-methylcatechol has been studied in acidic media, and the rate of 1 1 (and 1 2) complex formation between silver(II) and several diols is an order of magnitude higher in basic solution than in acidic. The kinetics of formation and dissociation of the complex between cop-per(II) and cryptand (2,2,1) in aqueous DMSO have been measured and the dissociation rate constant, in particular, found to be strongly dependent upon water concentration. The kinetics of the formation of the zinc(II) and mercury(II) complexes of 2-methyl-2-(2-pyridyl)thiazolidine have been measured, as they have for the metal exchange reaction between Cu " and the nitrilotriacetate complexes of cobalt(II) and lead(II). Two pathways are observed for ligand transfer between Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) and their dithiocarbamate complexes in DMSO the first involves dissociation of the ligand from the complex followed by substitution at the metal ion, while the second involves direct electrophilic attack by the metal ion on the dithiocarbamate complex. As expected, the relative importance of the pathways depends on the stability of the complex and the lability and electrophilic character of the metal ion. 

Consequently, different factors such as (i) silver ion coordination or solvation by the IL anions and/or cryptand 222 ligand, (ii) junction potential, and (iii) effect of IL nature on the of Fc (discussed below) could simultaneously be operative and responsible for the observed potential variation [20]. The stable lifetime of the [ Agl Ag 222, CH3CN] reference electrode is about 4 weeks and, thereby, similar to that reported by Snook et al. [19], even when the sdver(I) stability is increased by the formation of the Ag+-222 inclusion complex [30]. 

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