Salt Complexes with Calixarenes

The experiments described above in Sections 6.1-6.4 focus on the cation or the anion of a salt as separate, essentially non-interacting, entities. The experiments 

Casnati, A. Fochi, M. Minari, P. Pochini, A. Reggiani, M. Ungaro, R. Reinhoudt, D.N. Gazz. Chim. Ital. 1996, 126, 99. 

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The calix[5]arene 43, synthesized by Parisi et aL, for example, presents a marked shape and size selectivity even in ISEs for n-alkyl over iso-, sec-, and t rt-alkylammonium salts. It was proven that linear fz-alkyl ammonium salts form endo-complexes with the NH3+ head group interacting with the phenolic oxygen atoms and the alkyl residue with the calixarene cavity, while other branched alkyl ammonium salts generally form -complexes (see review for specific reference). 

But it is not always a case. Similar carboxylcalix[5]arene forms inclusion complexes with 1,10-decanediyldiammonium (Fig. 38.17c) and 1,12-dodecanediyldiammonium [39]. But it must be noticed here that the latest complexes are organic salts with 2 1 host guest stoichiometry as the calixarene host is a monoanion and the guest is a dication and additional, i.e. electrostatic interactions are playing important role in complex formation. 

From calixarene derivatives, through complexation with metal cation salts, new electrolytes are derived [M+CalixIX". Despite the fact that these new entities may find important applications in many aspects of research, not many efforts have... 

The chiral cavitands 3.109 have been developed by combining the amino acid residue L-alanine with macrocyclic cavitands (calixarenes - Section 3.14).51 These ammonium ion receptors are able to complex a range of amino acids and their methylester hydrochloride salts, all of which contain an -NH3+ functionality capable of interaction with the carboxylate residues of the host. In general amino acids are bound only very weakly in aqueous solution, while association constants with the chiral methyl esters range from 620 M-1 for L-tryptophan methylester to 110 M-1 for L-alanine methylester. The methylester of glycine is not bound at all. Receptors related to 3.109 with variable four peptide loops arrayed around a central calixarene core have been used to bind to the surfaces of proteins. The... 

Dodecaferrocene 64 (Figure 8.3) was prepared for the study of multiple redox centers. The calixarene core was constructed by the acid-catalyzed condensation of ferroce-necarboxaldehyde with resorcinol. Beer et alJ58 have also constructed poly Na+ salt 65 by the connection of crown ethers to bipyridine ligands, which were subsequently organized by the complexation to a Ru(n) metal core. 

The tube-like receptor 39 was shown to bind two imidazolidin-2-one molecules inside the calixarene subunits or, more interestingly, ion triplets comprising an anion, which binds to the central urea moieties, and two ammonium ions, which are incorporated into the calixarene rings [86]. Particularly stable complexes are formed with ammonium sulfate salts even in relative polar media (CD3OD/ CDCI3 3 1), but chloride ions can also induce the formation of such complexes... 

Synthesis and X-ray crystal structures of the first antimony and bismuth calixarene complexes have been described. The reaction of the monosodium salt of />-/f /-butylcalix[4]arene (BucC4) with 2equiv of SbC provided Bu OKSbCl. Bismuth calixarene complex was prepared by treatment of/>- r -butylcalix[8]arene with Bi[N(SiMe3>2]3 <2004CC1472>. 

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