Alkali metal ion pairing

In the case of alkali metals, ion pairing can be visualized as HFCs from paramagnetic nuclei of the metal cations associated with organic anion-radicals in ethereal solvents. In this respect, an alkali metal cation associated with the anion-radical of o-dimesitoylbenzene in DME or THF serves as a paradigm (Herold et al. 1965). 

The preparation of the first one was based on discoveries of Dye and Edwards concerning the dissolution of alkali metals potassium or sodium in an aprotic solvent, such as THE, containing a macrocyclic organic ligand e.g. 18-crown-6 or cryptand [2.2.2]. The specific procedure enables the preparation of an unique alkali metal supramolecular complex forming in THE solution alkali metal ion pairs, e.g. K /L/K" (where L = 18-crown-6 or 15-crown-5). 

Such alkali metal ion pairs are capable of two electron transfer from the potassium anion towards a suitable substrate, e.g. p-butyrolactone with formation of a respective carbanion. The strong tendency to two electrons transfer is due to the unusual oxidation state of potassium anion bearing on its outer s orbital a labile electron doublet shielded from the positive potassium nucleus by inner orbitals. Using 5 -enantiometr of P-butyrolactone as a monomer and potassium supramolecular complex as catalyst, enolate carbanion is formed as the first reactive intermediate which induces polymerization, yielding poly-(R)-3-hydroxybutanoate. The resulting biomimetic polyester has the structure similar to native PHB produced in nature, except for acetoxy-end-groups, which are formed instead of the hydroxyl ones typical for natural PHB. 

Thus, in a medium of low dielectric constant the ions will undergo ion association. Associated ions, such as ion pairs of 1 1 electrolytes will not contribute to the conductivity of the solution at low field strengths. Furthermore, Coulomb s law explains why ions of equal charge but of different size are associated to a different degree in a medium of given dielectric constant a compound consisting of big ions is more dissociated than one with small ions cesium hydroxide is a stronger base than potassium hydroxide. On the other hand, various halides of the alkali metal ions do not obey this law 2>. 

The complexes of alkali metal ions and of their salts described in paras. II—V may also be considered as lattice compounds because they do not necessarily persist in solution. Where the charge on the cation is neutralised by a small anion to give a salt, the solid may contain ion pairs coordinated by the additional ligand molecules, or the ions may be separated by the ligands, which usually form hydrogen bonds to the anion. When the cation is neutralised by a polydentate anion, the co-... 

The use of 2,2,2-cryptand and various crown ethers greatly reduces ion pairing in solution but affects only minor changes in the chemical shifts of the ions. Solvents that reduce K -Sng" ion paring through coordination of the alkali metal ion (e.g., en) also shift the 8 Sn values upheld relative to those solvents that are weakly coordinating (e.g., dmf Table 1). 

Niaura and Jakubenas [124] have studied the effect of alkali metal ions on the SERS spectra of phosphate anions adsorbed at Ag electrodes. The formation of ion pairs at the interface has been confirmed. 

Alkali metal ions, such as sodium and potassium, affect the saltiness of water, ion pairs, and p H, but generally do not cause adverse reactions in need of control by chelants. 

The counterion is quite important to the outcome of this reaction. Ion pairs, which form between alkali metal ions and the complex, induce CO lability which aids in the substitution process.1 1 Large charge-delocalized cations such as PPM are much less effective in forming ion pairs. The sulislilution process shown in Eq. 15.95 occurs readily when the counterion is Na but foils when it is PPN. Another good example of this effect can be seen by comparing NaICo CO)J and PPN [ Co[Pg.356]

Color Changes in Quartz. All quartz contains small amounts of substitutional Al, typically 0.01%, as well as similar amounts of interstitial hydrogen or alkali metal ions. When an Al3+ replaces a Si4+, one positive chaige is missing and electroneutrality is maintained by H+ or Na+, etc. Irradiation ejects one of a pair of electrons on an O adjacent to an AL... 

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. 

A significant rate enhancement for the C02 insertion process was noted in the presence of alkali metal counterions (Table I), even in the highly coordinating THF solvent. This rate acceleration was not, however, catalytic in alkali metal counterion, since the once formed carboxylate was observed to form a tight ion pair (76, 77) via its uncoordinated oxygen atom with the alkali metal ion, as evinced by infrared spectroscopy in the v(C02) region. That is, the counterion was consumed during the carbon dioxide insertion reaction. 

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... 

Depending upon the coordinated solvent around the metal, several interesting features have been described. The complex [Li(dioxane)4]+[Sn(furyl)3.Li(furyl)3Sn]. 2dioxane is an ion-pair consisting of lithium ion coordinated by four dioxanes and a complex anion. The latter consists of two pyramidal (furyl)3Sn ions linked by their furyl O-atoms to a central 6-coordinated Li center124. The stannyl potassium compound [K Sn(CH2Bu-f)3 (r/6-C6II5Me)3 is the first example of a complex in which the alkali metal ion is... 

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