Counter-cations

Table 11.17 Relative Selectivity of Various Counter Cations Table 11.18 Relative Selectivity of Various Counter Anions...

TABLE 11.17 Relative Selectivity of Various Counter Cations... 

Other factors also impact the type of crystals formed upon cooling of hot soap. Water activity or moisture content contribute to the final crystal state as a result of the different phases containing different levels of hydration. Any additive that changes the water activity changes the crystallization pathway. For example, the addition of salt reduces the water activity of the mixture and pushes the equiUbrium state toward the lower moisture crystal stmcture. Additionally, the replacement of sodium with other counter cations influences the crystallization. For example, the replacement of sodium with potassium drives toward the formation of 5-phase. 

The preparation and structural characterization of the ions HX2 has been an important feature of such work/ As expected, these H-bonded ions are much less stable than Hp2 though crystalline salts of all three anions and of the mixed anions HXY (except HBrI ) have been isolated by use of large counter cations, typically Cs+ and NR4+ (R = Me, Et, Bu") — see pp. 1313-21, of ref. 23 for further details. Neutron and X-ray diffraction studies suggest that [C1-H - C1] can be either centrosymmetric or non-centrosymmetric depending on the crystalline environment. An example of the latter mode involves interatomic distances of 145 and 178 pm respectively and a bond angle of -168 (Cl- -Cl 321.2pm).( >... 

Also of interest are the octacyano complexes, (M(CN)g] (M = Mo, W), whieh are commonly prepared by oxidation of the M" analogues (using MnO,) or Ce" ) and whose structures apparently vary, aceording to the environment and counter cation, between the energetically similar square-antiprismatic and dodecahedral forms. 

Since the cyanide anion is an ambident nucleophile, isonitriles R—NC may be obtained as by-products. The reaction pathway to either nitrile or isonitrile can be controlled by proper choice of the counter cation for the cyanide anion. 

Thus, by varying the etiolate counter-cation and the aldehyde, it was possible to... 

The most interesting results of the computational data, however, concern the addition of the second electron which is strongly endothermic in all cases. In other words, these dianions are predicted to dissociate an electron in the gas phase spontaneously. In solution or the solid state, it is possible that the ions could be stabilized by the effects of counter cations. This stabilization has been accomplished for the boron dianions which crystallized as contact ion pairs [47-50]. However, as indicated above, no success has been achieved so far in... 

Several variables were studied such as the counter cation(s) in the zeolite, the activation temperature, the solvent and the effect of additives. 

Positive- and negative-ion f.a.b. spectra of sulfated di-, tetra-, and hexa-saccharides from chondroitin sulfate have been reported. The spectra are characterized by multiple molecular-ions containing varying numbers of counter-cations to the sulfate and carboxylate anions, plus fragment ions... 

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