Cations as counterions

A cation-selective membrane (cation-exchange membrane) contains negatively charged fixed ions, mostly sulfonic acid groups, and cations as counterions, for example, H+ or Na+. In an anion-selective... 

The [M(CO)6] anions were isolated with solvated sodium or organic cations as counterions. [Ni(phen)3][Nb(CO)e]2 has also been obtained.721 The unsolvated Na[Ta(CO)6] is pyrophoric, and the Nb analog is light- and air-sensitive. 

The porous volumes measured by N2 adsorption are listed in Table 3. After the boronation, the total porous volumes (Vt) of the samples increase, corresponding to the increase of benzene adsorption capacity mentioned above. This should be resulted from the following aspects (1) The average mass of zeolite crystallite decrease and the number of crystal particles in unit weight of sample increases after the boronation owing to a limited introduction of trivalent atoms and Na+cations as counterions, as well as a severe dissolution of silicon. Thus, the total porous volume (mL/g) and the adsorption capacity increase. (2) The transformation of pore size occurs during the boronation. As shown in Table 3, the mesoporous volumes increase and the microporous volumes decrease after the boronation, meaning that some micropores are developed into mesopores due to the removal of silicon from the framework. This is also one of the important reasons why the total porous volumes as well as the adsorption capacities increase after the boronation. 

Molecular conductors have been constructed by using supramolecular cations as counterions to complex anions. For example, the charge-transfer salt Lio.6(15-crown-5)[Ni(dmit)2]2 H20 (dmit = 2-thioxo-l,3-dithiol-4,5-dithiolate) exhibits both electron and ion conductivity the stacks of the Ni complex provide a pathway for electron conduction, and stacks of the crown ethers provide channels for Li-ion motion. The /i-crown cation [Li(12-crown-4)](/i-12-crown-4) [Li(l2-crown-4)] has been generated as the counterion to [Ni(dmit)2]. The salt displays a room temperature conductivity of 30 S cm and exhibits a semiconductor-semiconductor phase transition on the application of pressure or on lowering the temperature. 

Table 8. Structural data of linear chain polyiodides with stacks of RRT cations as counterions... 

There is a wealth of crystal lattice types of interest in this review. We can differentiate between solid CT complexes and ion-radical salts. The former are the solid-state equivalents of the Mulliken solution CT complexes, and are the "two-chain" crystals. The latter are the so-called "one-chain" compounds, or ion-radical salts, where the organic cation (anion) crystallizes with inorganic anions (cations) as counterions. The crystal structure types have been reviewed by Herbstein [61], Tanaka [62], Soos [63-65] and many others. TaWes 1 and 2 update a classification introduced by Soos [63] and modified later by Wiygul et al. [66]. A few examples are shown diagrammatically in Fig. 4. The IS lattices are the ion-radical salts the IM lattices are the CT crystals, the crystal equivalents of the solution CT complexes. The 2S lattices are the first organic metals found (TTF-TCNQ). 

Fig. 5 Decomposition rates of the C-F bonds of Nation with various metal cations as counterions in 30% at 80°C (Fenton test) (Reproduced from Kinumoto et al. (2006). Copyright 2006, Elsevier Ltd)...

The anions belonging to groups one and three as well as N and CN- possess a nucleophilicity which is too strong and therefore form an ester bond which is too stable. For this reason, their activity as counterion during reactive cationic polymerization systems is insignificant. 

Polyelectrolytes are polymers having a multiplicity of ionizable groups. In solution, they dissociate into polyions (or macroions) and small ions of the opposite charge, known as counterions. The polyelectrolytes of interest in this book are those where the polyion is an anion and the counterions are cations. Some typical anionic polyelectrolytes are depicted in Figure 4.1. Of principal interest are the homopolymers of acrylic acid and its copolymers with e.g. itaconic and maleic adds. These are used in the zinc polycarboxylate cement of Smith (1968) and the glass-ionomer cement of Wilson Kent (1971). More recently, Wilson Ellis (1989) and Ellis Wilson (1990) have described cements based on polyphosphonic adds. 

The operation of a double-layer capacitor is tied to a displacement of electrolyte ions. In a fully charged capacitor, anions accumulate as counterions in the solution layer next to the positively charged electrode while the eoncentration of the cations decreases. At the negative electrode, the opposite situation is seen. During discharge, the ionic concentrations level out to the bulk solution values by migration and diffusion. 

Several crystal structure determinations of [AuX2l salts with different cations have been carried out for [AuC12],1823,1904,2854,3065-3068 [AuBr2],3065,3069,3070 or [AuF]-.3065 3066 3071-3074 Many other structural determinations have been reported in which [AuX2]- salts act as counterions of conducting or superconducting ion radical salts as bis-ethylenedithiotetrathiafulvalene (ET) and related organic donors. 

A remarkable feature of iridium enantioselective hydrogenation is the promotion of the reaction by large non-coordinating anions [73]. This has been the subject of considerable activity (anticipated in an earlier study by Osborn and coworkers) on the effects of the counterion in Rh enantioselective hydrogenation [74]. The iridium chemistry was motivated by initial synthetic limitations. With PFg as counterion to the ligated Ir cation, the reaction ceases after a limited number of turnovers because of catalyst deactivation. The mechanism of... 

Of the nonmetal oxyanions, those of carbon have a different role in soil than nitrogen and phosphorus. Bicarbonate and carbonate can act as counterions to cations to keep the soil electrically neutral. They are also important because all pH changes in soil tend to involve either carbonate or bicarbonate, and thus, both are involved in soil pH and buffering. 

Most of the work on chiral recognition in the ground state deals with salts having chiral, primary alkylammonium cations. Another approach is the chiral discrimination between two enantiomeric anions present as counterions in metal-cation complexes (Lehn et al., 1978). Discrimination between enantiomeric transition states will be dealt with in the next section together with non-chiral mimicry of enzymic catalysis. 

Low-lying vacant orbitals of alkali metal cations can, consequently, accept an unpaired electron density even if it is delocalized over an extended n system of carbon chains. The anion-radical of 1,4-diphenylbutadiene can exist in i-trans and in -cis forms. The relative amounts of these geometrical isomers appear to depend highly on the counterion/solvent system. Li and K+ were studied as counterions THF, 2-MeTHF, and DME were employed as solvents (Schenk et al. 1991). Interaction between the anion-radical and the cation contributes to a stabilization of... 

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