Solvation alkali metal ions

J. M. Lisy, Spectroscopy and structure of solvates alkali metal ions. Int. Rev. Phys. Chem. 16, 267 289 (1997). 

Crown ethers or cryptates 493) are cyclic polyethers that selectively solvate alkali-metal ions, although depending on the size of the hole, other ions can be extracted by these reagents. Some recent work on extraction using these crown ethers has been reported 494-496) and more results can soon be expected from the use of crown ketones 408, 409). 

Solvents also play an important role in regulating the reactivity of anions. Hexamethylphosphoric triamide (HMPT) solvates alkali metal ions so strongly that the counteranions are practically free. Under such conditions the inherent bond strengths determine the ease of reaction. Since the O-C bond is stronger than the C-X bonds (X = Cl, Br, I), facile displacement of halide ions by carboxylates in HMPT is a logical consequence (35-38). 

The cavity of a crown ether is a polar region, and the unshared pairs of electrons on the ether oxygens can solvate alkali metal ions. 

Preferential solvation has also been much studied using NMR of the (solvated) alkali metal ion for instance Rb" in water-methanol mixtures (105), in water-methanol mixtures (106) and aqueous mixtures of simple amides (107), %a and in binary mixtures of water (H2O and D2O) and methanol, formamide, or dimethyl sulfoxide (108), etc. 

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

The study of solvated alkali metal allyl species remains a complex topic due to a variety of reorganization processes. Structural data on alkali metal allyl derivatives include [G3H5Li(TMEDA)] 133,139 where solvated lithium ions act as... 

Furthermore, the applicability of the donicity rule may be unexpected for the solvation of alkali metal ions, where a complete explanation of the observations may be provided by considering electrostatic interactions between ion and dipolar solvent molecules. 

Ion solvation has been studied extensively by potentiometry [28, 31]. Among the potentiometric indicator electrodes used as sensors for ion solvation are metal and metal amalgam electrodes for the relevant metal ions, pH glass electrodes and pH-ISFETs for H+ (see Fig. 6.8), univalent cation-sensitive glass electrodes for alkali metal ions, a CuS solid-membrane electrode for Cu2+, an LaF3-based fluoride electrode for l , and some other ISEs. So far, method (2) has been employed most often. The advantage of potentiometry is that the number and the variety of target ions increase by the use of ISEs. 

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... 

The Born equation, modified by the inclusion of empirical correction terms for the radii of the solvated ions, was used to calculate shifts in the polarographic halfwave potentials of the alkali metal ions in different solvents.35... 

Highlights in the chemistry of cyclopentadienyl compounds have been reviewed.65 Trends in the metallation energies of the gas-phase cyclopentadienyl and methyl compounds of the alkali metals have been studied by ab initio pseudopotential calculations. Whereas there is a smooth increase in polarity of M-(C5H5) bonds from Li to Cs, lithium appears to be less electronegative than sodium in methyl derivatives. The difference between C5H5 and CH3 derivatives is attributed to differences in covalent contributions to the M-C bonds. In solution or in the solid state these trends may be masked by the effects of solvation or crystal packing.66 The interaction between the alkali metal ions Li+-K+ and benzene has also been discussed.67... 

Both associated and nonassociated electrolytes exist in sea water, the latter (typified by the alkali metal ions U+, Na-, K+, Rb+, and Cs-) predominantly as solvated free cations. The major anions. Cl and Br, exist as free anions, whereas as much as 20% of the F in sea water may be associated as the ion-pair MgF+. and 103 may be a more important species of I than I-. Based on dissociation constants and individual ion activity coefficients the distribution of the major cations in sea water as sulfate, bicarbonate, or carbonate ion-pairs has been evaluated at specified conditions by Garrels and Thompson (19621. 

All metal ions undergo some form of coordination with sulfoxides. Alkali metal ions are solvated by DMSO in much the same way as they are by water and show many parallels with corresponding hydrates. 

In very dilute metal solutions where dissociation is considered complete, the alkali metal ion is considered to be a normal solvated ion, as in electrolytic solutions, and it is generally conceded that the large volume change is to be ascribed chiefly to the solvated electron. As the concentration is increased it is quite obvious from conductance and magnetic data that metal ions interact with electrons to form some sort of an ion pair and also that electrons couple to form spin-paired species. The manner in which these species form is not entirely clear, nor is their... 

PRINCIPLES OF SOLVENT EXTRACTION OF ALKALI METAL IONS UNDERSTANDING FACTORS LEADING TO CESIUM SELECTIVITY IN EXTRACTION BY SOLVATION Bruce A. Moyer and Yunfu Sun... 

Paramagnetic States Ion Pairs to Solvated Alkali Metal Atoms... 

Acetonitrile. Acetonitrile is resistant to both oxidation and reduction, is transparent in the region 200-2000 nm, and is an excellent solvent for many polar organic compounds and some inorganic salts. Its dielectric constant of 37 permits reasonably high conductivities, although there is evidence of some association (see Table 7.8). It is less basic than dimethylformamide and dimethyl sulfoxide, and therefore does not solvate alkali metal cations as strongly. However, acetonitrile forms stable complexes with Ag(I) and Cu(I) ions. 

A useful probe of the immediate chemical environment of solute ions is the NMR chemical shift of alkali metal ions obtained in binary solvent mixtures [111, 126, 295]. These measurements are based on the assumption that the chemical shift of the solute cation is determined in an additive fashion by the solvent molecules comprising the first solvation shell. For example (cf. Fig. 2-11), the iso-solvation point of Na in dimethyl sulfoxide/acetone mixtures occurs at xxO.21 cmol/mol dimethyl sulfoxide, indicating the higher solvating ability of this solvent relative to acetone. As shown schematically in Fig. 2-11, the preferential solvation of Na by dimethyl sulfoxide displaces its chemical shift towards <5dmso and a deviation from the straight line is observed. 

Ill] A. I. Popov The Use of Alkali Metal Nuclear Magnetic Resonance in the Study of Solvation and Complexation of Alkali Metal Ions, in J. F. Coetzee and C. D. Ritchie (eds.) Solute-Solvent Interactions, Dekker, New York, London, 1976, Vol. 2, p. 271ff. A. I. Popov Alkali Metal, Mag-nesium-25, and Silver-109 NMR Studies of Complex Compounds in Nonaqueous Solvents, in G. Mamantov (ed.) Characterization of Solutes in Non-Aqueous Solvents, Plenum Publ. Corp., New York, 1978. [111a] P. Laszlo Kernresonanzspektroskopie mit Natrium-23, Angew. Chem. 90, 271 (1978) Angew. Chem. Int. Ed. Engl. 17, 254 (1978). [112] N. A. Matwiyoff, P. E. Darley, and W. 

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