Calixarenes alkaline earth metal complexes

Polycarboxylate crown ethers such as (205) are suitable ligands for potentiometric studies of mixed-metal complexes of Al3+ and alkali or alkaline-earth cations.303 A similar (+)-18-crown-6-tetracarboxylic acid, chemically immobilized on a chiral stationary phase (CSP), can selectively recognize both enantiomers of some analytes.304 Calixarene polycarboxylates such as (206) and (207) are useful ligands toward alkali-305,306 and also transition-metal ions,307 308 with applications in... 

Since the partitioning of metal ions from aqueous solutions into ionic liquids is inefficient as a result of the tendency of the metal cations to remain hydrated in the aqueous phase, additional extractants, such as crown ethers [185], calixarenes [186], dithizone [187], and others [188-214], were used. These species significantly enhance the partitioning of metal ions by forming complexes. Most of the research work has been concentrated on the extraction and separation of radioactive metals [187, 188, 191, 192, 196-213], alkali metals [185, 186, 193, 194], heavy metals [184, 192-196], and rare earth metals [197-215] and Aluminnm [216, 217]. The work reported in this field has been reviewed by Zhao et al. [190] and Chen et al. [211]. The progress made in IL extractions of metal ions (alkali, alkaline earth, heavy metals, radioactive elements, and rare earth) in recent years has been encap-snlated in Table 5.5. 

Although the calixarene carboxylic acids form complexes with some of the alkali metal cations, the fact that they have an even greater capacity for alkaline earth cations was first realized in the mid 1980s and subsequently studied in some detail. As a consequence of their greater charge the alkaline... 

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