Solvated Metal Ions

Equation (4.5) is also valid in this case. Reactions of this type are realized in polarography at a dropping mercury electrode, and the standard potentials can be obtained from the polarographic half-wave potentials ( 1/2)- Polarographic studies of metal ion solvation are dealt with in Section 8.2.1. Here, only the results obtained by Gritzner [3] are outlined. He was interested in the role of the HSAB concept in metal ion solvation (Section 2.2.2) and measured, in 22 different solvents, half-wave potentials for the reductions of alkali and alkaline earth metal ions, Tl+, Cu+, Ag+, Zn2+, Cd2, Cu2+ and Pb2+. He used the half-wave potential of the BCr+/BCr couple as a solvent-independent potential reference. As typical examples of the hard and soft acids, he chose K+ and Ag+, respectively, and plotted the half-wave potentials of metal ions against the half-wave potentials of K+ or against the potentials of the 0.01 M Ag+/Ag electrode. The results were as follows ... 

Conversely, an increase or decrease in the value of Dt] reflects a decrease or increase in the radius of the solvated metal ion. This works as a criterion in determining the effect of solvents on metal ion solvation. 

The strength of metal ion solvation affects not only the half-wave potentials but also the rates of electrode reactions of metal ions. For the reduction of a given metal ion, the reaction rate tends to decrease with increasing strength of solvation. The linear relation in Fig. 8.5 was obtained for the reduction of a sodium ion AG°v(Na+) is the solvation energy of Na+ and ks is the standard rate constant at the formal potential [23 a].2 For alkali metal ions in the same solvent, the rate... 

Partial molar volumes of electrolytes may present an additional difficulty if the partial molar volumes of individual constituent ions are needed. The subject has been dealt with as part of a valuable discourse on metal ion solvation.158 For species in water and some other solvents, the reference point for calculation of other partial molar volumes of single ions is the partial molar volume of the solvated proton, although there have been different views on what this value should be.159 However, the variation in values is not large and the consequence of choice of value does not have a huge impact particularly for large ionic species. Theoretical models of partial molar volumes of hydrated ions have been developed in order that estimates of them can be calculated. 160-162... 

Since 1967 when C. Pedersen discovered the class of compounds known as crown ethers, literally thousands of applications have been developed in which their ability to complex metal ions, solvate inorganic and organic salts in polar and non-polar solvents and facilitate anionic reactions have been exploited.10 The compounds cure cyclic polyethylene oxides. Two obstacles have prevented their wider utilization, particularly in commercial processes. Current synthetic methods are extremely costly. The materials have generally high levels of toxicity. Both these factors coupled with the difficulty in removing the crown ethers by processes other than distillation have hindered wider applications. 

One of the most promising areas of application of magnetochemistry is the study of transition metal complexes, in both the solid and dissolved states. Accordingly, magnetic susceptibility measurements may provide valuable information on the structures of solutions containing transition metal ions or complexes, on the symmetry conditions of transition metal ion solvates, etc. From magnetic measurements it is possible to establish the electronic structure of the central atom of the transition metal complex, its oxidation state and, in certain cases, its symmetry conditions. 

Yang, D. S. In Advances in Metal and Semiconductor Clusters, Volume 5 Metal Ion Solvation and Metal-Ligarul Interactions. Duncan, M. A., Ed. Elsevier Amsterdam, 2001, pp 187-226. 

Gallium(III) ion takes the six-coordinate solvation structure in trimethyl phosphate (TMP) as in water from the measurement of EXAFS and the comparison between some metal ion solvation. The results also show the bond length between the solvated metal ion (Mn , Fe , Co , Ni , Cu , or Ga ) and oxygen atom of each solvent (EtOH, MeOH, DMSO, TMP) is much similar to that in water. However, the coordination number of the Zn ion even in the larger ionic radius than the Gd", decreases in DMA and TMP, i.e., the coordination of DMA or TMP with such metal ions may influence their charge density than ionic radius. 

Stace AJ (2002) Metal ion solvation in the gas phase the quest for higher oxidation states. J Phys Chem A 106 7993-6005... 

J. Burgess, Metal Ion Solvation, EUis Horwood, Chichester (1978). 

Gutmann s DN values are based on reaction enthalpies, so a correlation with SH rather than with AG is not unreasonable. This tentatively emerging correlation with DN values is, however, easily upset by steric factors, either in the form of ligand bulk 2 or of solvent bulk. Activation enthalpies for solvent exchange at metal(ii) centres, for instance Fe +, do not correlate satisfactorily with values, nor do activation enthalpies for Na+ release from the 2,2,2-cryptate (1). The noncorrelation of activation enthalpies with DN values in many systems need not cause too much surprise, as these DN values are based on enthalpies of reaction of the respective solvents with antimony pentachloride, a process significantly different from that involved in metal ion solvation. 

Lithium ions are generally solvated by IL ions to form metal-ion solvation complexes. Electrochemical and physicochemical properties of the lithium-containing IL solutions, such as ionic conductivity, redox reaction behavior, viscosity, and density, strongly depend on the static and dynamic structures of the mentioned solvation complexes. Chapter 10 discusses recent progress in lithium... 

Umebayashi Y, Yamaguchi T, Fukuda S, Mitsugi T, Takeuchi M, Fujii K, Ishiguro S (2008) Raman spectroscopic study on alkaline metal ion solvation in l-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid. Anal Sci 24 1297... 

Mixed solvent systems are often used to probe solvent effects and in this context the molecular composition of the metal-ion solvation sphere is critical. NMR measurements in acetonitrile/water systems show that for Li, where the coordination number is four, water replaces acetonitrile completely until the waterrU" " ratio is 4 1. For Na" and K, water replaces acetonitrile completely until the watenmetal ion ratio is around 1 1 and then the NMR signal parallels the shift in the bulk solvent acetonitrile/water mixture. 

---