Crystallinity, organic ionic

We discuss crystalline inorganic ion exchangers, such as [97,98,104,134-146] zeolites, hydrotal-cites, alkali metal titanates, titanium silicates, and zirconium phosphates, and also organic ionic exchangers such as the ion-exchange resins. However, details are given only in the case of the archetypal crystalline ionic exchangers, that is, aluminosilicate zeolites [97,98,104,134]. 

However, it should be mentioned that the dissolution process of a solid, crystalline complex in an (often relatively viscous) ionic liquid can sometimes be slow. This is due to restricted mass transfer and can be speeded up either by increasing the exchange surface (ultrasonic bath) or by reducing the ionic liquid s viscosity. The latter is easily achieved by addition of small amounts of a volatile organic solvent that dissolves both the catalyst complex and the ionic liquid. As soon as the solution is homogeneous, the volatile solvent is then removed in vacuo. 

Likewise, cationic acceptors afford mixed (positively) charged complexes with electron-rich donors,11 i.e., [D, A+] and anionic donors associate with electron-poor acceptors to form mixed (negatively) charged complexes,12 i.e., [D-, A]. In each case, the intermolecular (ionic) complexation or association represents the highly oriented organization of the donor/acceptor pair (independently of whether they bear positive, negative or no charge) that is often sufficient to afford crystalline complexes amenable to direct X-ray structure elucidation.13... 

Crystalline salts of many organic acids and bases often have a maximum solubility in a mixture of water and water-miscible solvents. The ionic part of snch a molecule requires a strongly polar solvent, snch as water, to initiate dissociation. A mixture of water-miscible solvents hydrates and dissociates the ionic fraction of pollutants at a higher concentration than wonld either solvent alone. Therefore, from a practical point of view, the deliberate nse of a water-soluble solvent as a cosolvent in the formnlation of toxic organic chemicals can lead to an increased solnbility of hydrophobic organic contaminants in the aqueous phase and, conse-qnently, to a potential increase in their transport from land surface to groundwater. 

Work along these lines could give a better understanding of the role played by ions in the radiation chemistry of polymers. The fact that ions can induce chemical reactions in irradiated organic solids is clearly demonstrated by the polymerization of certain crystalline monomers which are known to polymerize only when treated with ionic catalysts (3). 

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