Calixarenes alkali metal complexes

E-3 (Figure 10.26) is the first example of an ionophoric calixarene with appended fluorophores, demonstrating the interest in this new class of fluorescent sensors. The lower rim contains two pyrene units that can form excimers in the absence of cation. Addition of alkali metal ions affects the monomer versus excimer emission. According to the same principle, E-4 was designed for the recognition of Na+ the Na+/K+ selectivity, as measured by the ratio of stability constants of the complexes, was indeed found to be 154, while the affinity for Li+ was too low to be determined. 

The cation-7t interactions were evidenced by Prodi, who studied the photophysical properties of calix[4]arene-crown and their complexes with alkali metal ions. The presence of these cation ions usually caused weak effects on the absorption spectra, but sometimes caused marked changes in the intensity and wavelength maxima of the fluorescence bands of the calixarenes. The fluorescence quantum yields of complexes with alkali metal follows a precise trend for both MC46 and MC7, decreasing from potassium to cesium. These changes were explained by cation-Tt interactions between the metal ion and the two aromatic rings pointing toward it.30... 

One of the important applications of butylcalix[4]arenes arises from their ability to trap alkali metal ions. In particular, Cs+-calixarene complexes have received much attention because of the need to remove the Cs radionucleotide from nuclear wastes. Benevelli et al. have used one-pulse solid state NMR experiments to directly observe Li, Na and Cs ions in the host cavity [52]. More advanced experiments, which allow the investigation of metal lattice interactions were also reported. Rotational-echo double resonance (REDOR) NMR is a useful tool for obtaining structural details of butylcalix[4]arene [53]. Gullion and coworkers used REDOR to determine the position of the... 

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... 

The unsubstituted para-t-butyl calixarenes themselves complex metals via their aryloxide groups. Since aryloxide complexes are frequently oligomeric, the simple calixarenes do not give monomeric complexes. Aryloxides are hard ligands, therefore they readily form complexes with oxo-philic hard metal ions such as alkali metals, early transition metals, lanthanides, and actinides. Complexation is often inferred because the calixarene acts as a carrier for the metal ion from an aqueous to an organic phase. With the /wa-/-butylcalix[ ]arenes in alkaline solution, a value of n = 6 gives the best carrier for lithium(I), sodium(I), and potassium(I), with a value of n 8 giving the best carrier for rubidium(I) and caesium(I).15,16 Titanium(IV) complexes have been characterized,17-19 as well as those of niobium(V) and tantalum(V).20-22 These complexes are classified as... 

Only few investigations have been published on the gas-phase ion chemistry of host-guest complexes of calixarenes. With the advent of ESI mass spectrometry, especially when combined with ion-trap and FT-ICR mass spectrometry, this field has started to be developed. Binding selectivities of alkali metal ions to cahxarene-based crown ethers and open-chain ethers have been studied , the inclusion of neutral guests into the protonated resorcarene-based cavitand hosts by gas-phase ion-molecule reactions with amines have been studied and the formation of capsules from various calixarene tetraether derivatives and alkylammonium ions as ionic guests (notably enabling their detection by mass spectrometry) have been described recently . ... 

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. 

P-5 A phosphinic calixarene is complexed to four Ag(I)Q molecules and one additional chloride ion to give an anion (161) that can act as host for alkali metal cations, Hg(II) and Pb(II)235 236. 

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... 

The calix[4]arene 34 and bis calix[4]arene 35 derivatives were generated by bridging their lower rim oxygen with one 2,6-lutidyl unit or two of these at 1,3-distal positions of calixarene scaffolds. The calixarenes 34 and 35 showed complexation toward alkali metal cations (2000T3121). 

Given the structural analogy with the crown ethers, the calixarenes were alkylated to produce ether ligands at the phenolic face. These molecules complex various cations including alkali metals ions. Complexation may take place... 

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