Cation/anion complex formation

CAM] Caminiti, R., Nickel and cadmium phosphates in aqueous solution. Cation-anion complex formation and phosphate - H2O interactions, J. Chem. Phys., 77, (1982), 5682-5686. Cited on page 205. 

Novel anions stabilized by alkali-polyether cations The ability of a crown (such as 18-crown-6) or a cryptand (such as 2.2.2) to shield an alkali cation by complex formation has enabled the synthesis of a range of novel compounds containing an alkali metal cation coordinated to a crown or cryptand for which the anion is either a negatively charged alkali metal ion or a single electron (Dye Ellaboudy, 1984 Dye, 1984). Such unusual compounds are called alkalides and electrides , respectively. 

The C—Ph bond in compounds 432 (R = Ph) or 438 may be cleaved easily by I2 or Hgl2, leading to formation of Phi or PhHgl and the corresponding iodo derivatives or cation-anion complexes with tetrahedral tin in the cation and a Hgl3 anion555. 

Figure 7.1. Solubility of simple salts as a function of the common anion concentration (Example 7.2). The cations and anions of these salts do not protolyze in the neutral pH range. The equilibrium solubility is given by the metal-ion concentration. At high anion or cation concentration, complex formation or ion-pair binding becomes possible (dashed lines). If the salt is dissolved in pure water (or in an inert electrolyte), the solubility is defined by the electroneutrality z[Me" J = /i[anion ]. If z = n (e.g., BaS04), the solubility is given by the intersection (-I-). If z the electroneutrality condition is fulfilled at a point slightly displaced from the intersection (t). The insert exemplifies the solubility equilibrium for Cap2 ( o = 10" ) and lists the domains of over- and undersaturation.

Interpretation of data given in Table 2 is more difficiilt than in the case of polarographic reduction of metal cations, since complex formation is also influenced by anion solvation. Different solvents can differ considerably in their solvating ability towards anions, and this is especially true for protic and aprotic solvents (10, 43, 49, 50). 

We concluded that formation of the cationic-anionic complex inside the cuticle is necessary to produce this effect. If the cell membrane complex is damaged (e.g., by permanent waving), then penetration is enhanced. Adsorption of the cationic species occurs inside the cell membrane complex and the endocuticle. On washing with the anionic surfactant, penetration occurs, and an insoluble cationic-anionic complex deposits inside the cell membrane... 

In a general (and generalizing) view on this issue it can be stated that suitably selected ionic liquids are very likely to form catalytically active ionic catalyst solutions with a given transition metal catalyst if the latter is neither extremely electrophilic (acidic) nor extremely nucleophilic (basic). While extremely electrophilic catalyst complexes are likely to coordinate strongly even with those anions of the ionic liquid solvent which are generally regarded as weakly coordinating, extremely nucleophilic catalytic centers are likely to react with the ionic liquid s cation. Carbene complex formation by oxidative addition as well as dealkylation of the cation are possible deactivation pathways of the catalyst in such a case. 

The notion of a polyelectrolyte complex is well established for the mixture of two homopolymers one anionic, the other cationic. The complex formation is generally associated with a phase separation (often a precipitation) although water soluble polymeric complexes are known. Only few data are available when the charge density of the polyelectrolytes is progressively decreased. This situation is exemplified with a series of mixtures of polyacrylamide derivatives, one family of copolymers has various contents in anionic units, the other is similar but with cationic units. We found that even for a few percent in ionic units, the mixtures water/copolymer anionic/copolymer cationic phase separates a polymer rich phase (including the two types of copolymers) is in equilibrium with a very diluted polymer solution. 

Despite numerous efforts, there is no generally accepted theory explaining the causes of stereoregulation in acryflc and methacryflc anionic polymerizations. Complex formation with the cation of the initiator (146) and enoflzation of the active chain end are among the more popular hypotheses (147). Unlike free-radical polymerizations, copolymerizations between acrylates and methacrylates are not observed in anionic polymerizations however, good copolymerizations within each class are reported (148). 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

It has been shown that the effects found are caused by specific solvation of both the PhAA ionogenic and other polar groups by the plasticizers used, as well as by the influence of ion-exchangers nature on the PhAA cations-anionic sites complex formation constants. 

Dagnall and West8 have described the formation and extraction of a blue ternary complex, Ag(I)-l,10-phenanthroline-bromopyrogallol red (BPR), as the basis of a highly sensitive spectrophotometric procedure for the determination of traces of silver (Section 6.16). The reaction mechanism for the formation of the blue complex in aqueous solution was investigated by photometric and potentiometric methods and these studies led to the conclusion that the complex is an ion association system, (Ag(phen)2)2BPR2, i.e. involving a cationic chelate complex of a metal ion (Ag + ) associated with an anionic counter ion derived from the dyestuff (BPR). Ternary complexes have been reviewed by Babko.9... 

If the nucleophilicity of the anion is decreased, then an increase of its stability proceeds the excessive olefine can compete with the anion as a donor for the carbenium ion, and therefore the formation of chain molecules can be induced. The increase of stability named above is made possible by specific interactions with the solvent as well as complex formations with a suitable acceptor 112). Especially suitable acceptors are Lewis acids. These acids have a double function during cationic polymerizations in an environment which is not entirely water-free. They react with the remaining water to build a complex acid, which due to its increased acidity can form the important first monomer cation by protonation of the monomer. The Lewis acids stabilize the strong nucleophilic anion OH by forming the complex anion (MtXn(OH))- so that the chain propagation dominates rather than the chain termination. 

The composition of the electrolyte is quite important in controlling the electrolytic deposition of the pertinent metal, the chemical interaction of the deposit with the electrolyte, and the electrical conductivity of the electrolyte. In the case of molten salts, the solvent cations and the solvent anions influence the electrodeposition process through the formation of complexes. The stability of these complexes determines the extent of the reversibility of the overall electroreduction process and, hence, the type of the deposit formed. By selecting a suitable mixture of solvent cations to produce a chemically stable solution with strong solute cation-anion interactions, it is possible to optimize the stability of the complexes so as to obtain the best deposition kinetics. In the case of refractory and reactive metals, the presence of a reasonably stable complex is necessary in order to yield a coherent deposition rather than a dendritic type of deposition. 

In the second cluster, the two Ru6 octahedra are linked through two palladium atoms. The third cluster contains two additional palladium atoms. The Pd4 skeleton adopts the form of a bent square. The two Ru6 octahedra have local structures similar to those in the second cluster, but their relative orientation is now twisted. Apparently, formation of these heterometallic cluster complexes does not result from a simple combination reaction between cationic and anionic complexes but is accompanied by partial redox reactions.900... 

The complexing of chitosan and its basic derivatives with anionic substances is paralleled by compatibility with cationic and nonionic compounds. Similarly, the anionic derivatives of chitosan show complex formation with cationic agents and are compatible with anionic and nonionic compounds. The capability of these chitosan derivatives to complex with certain metal ions, notably those of the transition series, is also important, having possibilities for the removal of metal salts from effluent. The hierarchy in terms of binding capacity is Cr(III) < Cr(II) < Pb(II) < Mn(II) < Cd(II) < Ni(II) < Fe(II) < Co(II). 

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