Alkaline-earth Counterions

Mathis, L. Christmann-Lamande, and B. Francois, J. Polymer Sci., Polymer Chem., 1978, 16, 1285. 

Christmann-Lamande, C. Mathis, and B. Francois, Compt. rend., 1978, 286, C, 651. 

Propagation by dicarboanionic polystyryl barium has also been examined in some detail.Meticulous ultraviolet/visible absorption and conductance studies of THF and tetrahydropyran solutions have proved the dicarboanionic nature of the system. Furthermore, the absorption maximum of the anions varies with the degree of polymerization (D.P.) of the living oligomers present, and together with other evidence points to the existence of cyclic species (22). Investigations of fluorenyl barium in THF show a sandwich-type structure with Ba ions located between cyclopentadienyl rings, and a 

While it is possible to imagine other complex structures, such as cyclic aggregates and rosette formations, which might arise in the dicarboanionic systems. 

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Although there seems to be a small but definite influence of the nature of the monovalent counterion on and (Figure 7), a much more spectacular effect is observed if the monovalent ion is partially or totally replaced by a bivalent alkaline earth counterion (Figure 8). In general rises with increasing ratio up to a... 

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

It is common practice in pharmaceutical industry to generate salt forms of a drug substance to improve solid-state properties and solubility. CE has proven its ability to analyze reliably organic acids (direct, indirect detection) and alkaline/earth alkaline metals and basic amino acids. For basic drugs, a non-toxic organic acid or inorganic acid is chosen as counterion. Acidic drug substances will usually be deprotonated by alkaline and earth alkaline... 

Ion chromatography is a convenient method for simultaneous determination of alkali, alkaline earth and ammonium ion concentrations in solution. The identity of the analytes is set by the retention times and quantation is carried out by a detector. Conductivity is frequently used, after chemical suppression of the eluate, by which chloride counterions were exchanged by hydroxide. UVV spectrophotometric measurement of hydroxide ions at 200 nm was proposed as an alternative method to suppressed conductivity. Both methods... 

The selective cation binding properties ol crown ethers and cryptands have obvious commercial applications in the separation of metal ions and these have recently been reviewed (B-78MI52103.79MI52102, B-81MI52103). Many liquid-liquid extraction systems have been developed for alkali and alkaline earth metal separations. Since the hardness of the counterion is inversely proportional to the extraction coefficient, large, soft anions, such as picrate, are usually used. 

The X-ray structure of the L-Sr(Picrate)2 (L = p-tert-butyl-calix[4]arene-tetra(diethylamide)) is reported, as well as MD simulations on the L M2+ complexes in vacuo, in water, and in acetonitrile solutions for alkaline earth cations with a comparison of converging and diverging conformers.130 In the simulated and solid-state structures of the L M2+ complex, the ligand wraps around the complexed cations M2+ (more than it does with alkaline cations), which are completely encapsulated within the polar pseudo-cavity of L, without coordination to its counterion in the crystal or to solvent molecules in solution. In contrast to alkali cation complexes, which display conformational flexibility in solution, computations show that the alkaline earth cation complexes are of the converging type in water and in acetonitrile. Subtle structural changes from Mg2+ to Ba2+ are observed in the gas phase and in solution. Based on FBP calculations, a binding sequence of alkaline earth cations was determined Mg2+ displays the weakest affinity for L, while Ca2+ and Sr2+ are the most stable complexes, which is in agreement with the experiment. 

Vayssiere, P., Wipff, G. (2003), Importance of Counterions in Alkali and Alkaline Earth Cation Extraction by 18-Crown-6 Molecular Dynamics Studies at the Water / SC-CO2 Interface, Phys. Chem. Chem. Phys. 5, 2842-2850. 

The present review deals mainly with two examples of polyelectrolyte phase behavior as discussed above. As an example for an H-type precipitation, the solution properties of polyvinylpyridinium chains are monitored as function of added inert salt. Here, we focus on the determination of the effective charge density and of the solvent quality parameter which are supposed to play a central role for the understanding of polyelectrolyte solution without specific counterion interactions. The second system under investigation comprises the interaction of polyacrylic acid with alkaline earth cations which exhibit very specific interactions, thus representing an example for type L-precipitation. Here the coil dimensions close to the phase boundary are compared to those close to type H-precipitation with inert added salt. 

A persistent radical-anion (4) may be prepared from dibenzofuran, the reduction of which by alkali or alkaline earth metal in liquid ammonia was reported in 1964. ° Gerdil and Lucken in 1965 also reported a preparation of 4 by reduction of dibenzofuran with potassium in DME its ESR spectrum and those of its sulfur and selenium analogs were solved. These authors also carried out a polarographic and spectroscopic study.Evans and co-workers reported ESR results for dibenzofuran closely similar to those of Gerdil and Lucken. The nature of the unimolecular decay of the anion-radical was studied and inferred to be C—O bond scission. The dependence of the rate of this reaction upon the counterion was investi-... 

Zeolites are open structures of silica in which some of the silicon atoms in the tetrahedral sites are replaced by aluminum ions [148-151]. Counterions like Na" and maintain the electroneutrality and reside freely at certain locations in the zeolite cages. Zeolites can be represented by the empirical formula M2/ Al203. xSi02 yH20, where M is an alkali metal or an alkaline earth metal cation of valence n,x>2, and y varies from 0 to 10. Depending on the Si/Al... 

In the context of crown ether hosts, non-covalent bonds of pole-pole, pole-dipole, and dipole-dipole types can all be employed [3-6] in the formation of host-guest complexes. Where the guest species is an alkali metal (i.e. Li, Na", K", Rb, Cs ), alkaline earth metal (i.e. Mg, Ca, Sr, Ba ), or harder transition or post-transition metal (e.g. Ag", TT, Hg, Pb, La, Ce ) cation [3-6,14], an electrostatic (M" O) pole-dipole interaction binds the guest to the host whilst the (M" X ) pole-pole interaction with the counterion (X ) is often retained. The features are exemplified by the X-ray crystal structure [15] shown in Fig. la for the 1 2 complex (1) (NaPF jj formed between dibenzo-36-crown-12 (1) and NaPF. Molecular complexes involving metal cations have considerable strengths even in aqueous solution and a template effect involving the metal cation is often observed during the synthesis of crown ether derivatives. 

A very strong reducing agent and the presence of suitable dopant counterions are needed to introduce divalent cations into polyacetylene. Such a strong reducing solution can be made by dissolving the alkaline earth metals, calcium, strontium or barium in liquid ammonia (equation 1). 

The properties of alkyl sulfates differ depending upon the structures of the alkyl chains and the counterions present. While alkali and ammonium salts are similar in behaviour, the solubilities of the alkaline-earth salts are reduced in water. On the other hand, the solubilities in organic solvents of alkyl sulfates with polyvalent ions is increased. Due to this fact, fatty pollutants can be better detached from fabrics by a detergent solution of moderate water hardness than by a solution showing extremely low water hardness. In particular, the wetting of textile fibres will be measurably accelerated by using calcium or magnesium as counterions. 

Ion-selective electrodes offer an observable value for the biologically relevant parameter the ion s active molality in the aqueous phase of the biological specimen directly. This might be a challenge for elements that are associated by 30-50% to different anions, e.g., magnesium and calcium. For alkaline and alkaline-earth metal cations the Debye-Hiickel formalism allows a fair approximation of the mean activity coefficient ji+ as measured for an ion and its counterion in a calibration solution. The notation of... 

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