Metal ions solvent exchange

Samanta, S. K. and Misra, B. M. Ion Exchange Selectivity of a Resorcinol-Formaldehyde Polycondensate Resin for Cesium in Relation to Other Alkali Metal Ions, Solvent Extr. Ion Exch, 13(3) (1995), 575-589. 

On the other hand, the impregnation process involves a combination of both adsorption of metal complex ions and deposition of the solute as the solvent is evaporated. Thus, the resulting metal dispersion depends on the fraction of metal ions undergoing exchange with support species relative... 

More elaborately, complex formation can be viewed as in Fig. 2 (the detailed kinetic implications of this refinement to the basic Eigen mechanism are covered by Benton and Moore [71]). It is reasonable to relate the rate coefficient for the dissociative slow stage with that for solvent exchange, since breaking of a metal ion—solvent bond is involved in both processes. 

The stereochemistry of hydrogen-deuterium exchange at the chiral carbon in 2-phenylbutane shows a similar trend. When potassium t-butoxide is used as the base, the exchange occurs with retention of configuration in r-butanol, but racemization occurs in DMSO. The retention of configuration is visualized as occurring through an ion pair in which a solvent molecule coordinated to the metal ion acts as the proton donor... 

Some species have a large number of exchangeable hydrogens. Thus, metal ions with many coordinated water molecules will become completely deuterated in D20. For example, Co(H20) + becomes Co(D20) +. If there were a 2 percent secondary kie per bond, it would be amplified to (1.02)12 or 1.27. It would not be a simple matter to demonstrate the operation of a primary kie in such a system because of this, given the p/f difference between the two metal ions and the general effects of the solvent change. 

Horwitz EP, Chiarizia R, Dietz ML, Diamond H, Nelson DM (1993a) Separation and preconcentration of actinides from acidic media by extraction chromatography. Anal Chim Acta 281 361-372 Horwitz EP, Chiarizia, R., Diamond H, Gatrone RC, Alexandratos SD, Trochimzuk AQ, Crick DW (1993b) Uptake of metal ions by a new chelating ion exchange resin. 1. Acid dependencies of actinide ions. Solvent Extr Ion Exch 11 943-966... 

Certain other metal ions also exhibit catalysis in aqueous solution. Two important criteria are rate of ligand exchange and the acidity of the metal hydrate. Metal hydrates that are too acidic lead to hydrolysis of the silyl enol ether, whereas slow exchange limits the ability of catalysis to compete with other processes. Indium(III) chloride is a borderline catalysts by these criteria, but nevertheless is effective. The optimum solvent is 95 5 isopropanol-water. Under these conditions, the reaction is syn selective, suggesting a cyclic TS.63... 

II. Solvent Exchange and Ligand Substitution on Main Group Metal Ions... 

B. Solvent Exchange on Divalent Octahedral First-Row Transition Metal Ions... 

Beryllium(II) is the smallest metal ion, r = 27 pm (2), and as a consequence forms predominantly tetrahedral complexes. Solution NMR (nuclear magnetic resonance) (59-61) and x-ray diffraction studies (62) show [Be(H20)4]2+ to be the solvated species in water. In the solid state, x-ray diffraction studies show [Be(H20)4]2+ to be tetrahedral (63), as do neutron diffraction (64), infrared, and Raman scattering spectroscopic studies (65). Beryllium(II) is the only tetrahedral metal ion for which a significant quantity of both solvent-exchange and ligand-substitution data are available, and accordingly it occupies a... 

The definition of solvent exchange rates has sometimes led to misunderstandings in the literature. In this review kjs 1 (or fc2lsolvent]), sometimes also referred to as keJ s 1, is the rate constant for the exchange of a particular coordinated solvent molecule in the first coordination sphere (for example, solvent molecule number 2, if the solvent molecules are numbered from 1 to n, where n is the coordination number for the solvated metal ion, [MS ]m+). Thus, the equation for solvent exchange may be written ... 

Generally the magnitudes of solvent exchange rate constants increase in the sequence NH3 > H20 > DMF > MeCN > MeOH, which is largely independent of the nature of the metal ion (108,109). This sequence cannot be readily identified with specific characteristics such as dielectric constant, donor number, electric dipole moment, or stereochemistry, and it appears to reflect the overall solvent characteristic. There may be a correlation between the AH for solvent exchange on [M(solvent)6]2+ and the heat of dissociation of solvent from this species (110). 

Although this review is primarily concerned with the solvent exchange and single ligand substitution on fully solvated metal ions, it is nevertheless appropriate to note that substitution of coordinated solvent in [M(solvent)e]2+ by other ligands can substantially alter the lability of the remaining solvent. This is illustrated for a range of... 

---