Ternary Crown Ether Complexes

6 Macropolycyclic Host Molecules Cryptands and their Cation Complexes 

Macropolycyclic ligands, commonly referred to as cryptands, contain intramolecular cavities of three-dimensional shape ( crypts ). In their complexes Q cryptates ) with alkali and alkaline earth cations, they display considerably enhanced stabilities with respect to crown ethers cryptate effect ) Thus, the K complex of 

The in-out and out-out forms have been detected in the crystal structures of N-borane-[l.l.l] and N,N-diborane-[2.2.2] where BHj groups are attached to the amine nitrogens. 

As in the case of monocyclic polyether ligands, the preferred conformations about C-C and C-O bonds are synclinal and antiperiplanar, respectively. The C—N—C—C, C—C—N—C torsion angles may lie in either of these low-energy ranges. 

The flexibility of the [2.2.2] cryptand is also evident from its complexes with larger ions such as Rb and Cs. If going from to Rb to Cs, the distance between the two bridgehead nitrogen atoms which is significant for the cavity size increases from 5.75 to 6.00 to 6.07 A, accompanied by a change of the mean torsion angle about C-C bonds from 54 to 67 to 70° Moreover, a N. .. N separation as 

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The effect of cation-complexing agents on the barium(II)-assisted basic ethanolysis of phenyl acetate has been looked at.184 Addition of various crown ethers yields ternary complexes of 1 1 1 crown-metal-ethoxide composition and a definite cation activation takes place. Cryptand 222 removes the catalytic activity. 

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

Other examples of ancillary ligands used to enhance analyte selectivity include amide-modified D03A (1,4,7,10-tetraazacyclododecane-l,4,7-trisacetate) complexed to Tb , which selectively binds the bidentate analytes p-dimethylaminobenzoic acid (DMABA) and SA (160-162). The binary complex of with EDTA can effectively detect SA, 4-aminosalicylic acid and 5-fluorosalicylic acid (163). [Tb(EDTA)] also has been used to detect catalysis of hydroxybenzoic acid (HBA) by hemin via formation of a ternary complex with the HBA oxidation product (164). Diaza-crown ethers have been utilized with and Eu to detect phthalate, benzoate,... 

As in the previous example, the chirality of the ligand is in close proximity to the palladium binding site, while the pendant group is achiral. Introduction of the crown ether was designed to enhance coordination to the counterion. A ternary complex including the crown ether, potassium cation, and the enolate anion was proposed in which the bulky crown ether blocks approach of the enolate to Cl and provides a chiral pocket around carbon C3 [40]. Enantioselectivities up to 75% were reported [40], which were later revised to 65% [38]. 

Inokuma et al have reported a further example of additions with crown ether derivatives. In this instance the additions are intermolecular and involve the dimerization of the vinylbenzene derivative (123) to afford the two adducts (124) and (125). The ion-complexing capabilities of the adducts were assessed. A layered ternary solid is formed between 1,2-dihydroxybenzene and trans- -(2-pyridyl)-2-(4-pyridyl)ethylene. Within this, the stilbene is held in a head-to-tail arrangement. Irradiation brings about the formation of a cyclobutane identified as (i )-c/ y,/ra y,/ra -l,3-bis(2-pyridyl)-2,4-bis(4-pyridyl)cyclobutane. An extension of this work to the use of 5-methoxyresorcinol as the template has demonstrated that quantitative yields of ladderanes (126) can be obtained by irradiation of the solid-state units represented as (127). The diazastilbene derivative (128) readily forms complexes with the tetra-acid (129). This acts as a supramolecular template and holds the ethene systems close enough for photochemical dimerization. ... 

Apparently the compounds 56) deviate so strongly from classical crown ether structures that other complexation factors — leading nevertheless to high enantio-selectivity — become important. Because only weak complexes are formed in solution interpretation of the results remains speculative. We ascribe, however, the formation of S-alcohols from L-amino acid derivative (56) to the formation of a ternary complex having the structure crudely represented in (65). The main stereochemical... 

Chen etal. synthesized a triptycene-based bis(crown ether) molecnlar cage that can bind diquat (l,l -ethylene-2,2 -bipyridininm) and electron-rich aromatics via charge transfer and face-to-face tt-stacking interactions, forming a stable ternary complex. For an appropriately chosen ternary complex with benzidine and diquat as the inclusion molecules, diquat can be removed and reassociated by adding acid and base. 

Figure 12 illustrates an anion transport system with a lanthanide tris(p-diketonate) as the carrier. When the lipophilic lanthanide complex is present in Membrane, a highly coordinated complex is formed with the anion guest at the interface between Aq. I and Membrane, and K(I) cation is extracted into Membrane as the counter-cation. The resulting ternary complex moves across Membrane. At the interface between Membrane and Aq. II, the guest anion is released into Aq. II together with its counter-cation. Crown ether carrier mediates anion transport in a In Chemical Separations with Liquid Membranes Bartsch, R., et al. ... 

Schall and Gokel have reported the construction of molecular boxes derived from nucleic acid bases and azacrown ethers [23]. Detailed NMR studies provided evidence for the association of A-crown-A with T-crown-T in chloroform. Formation of a ternary receptor complex with a, m-diammonium compounds (Figure 12) was also suggested. 

Huorescent crown-appended porphyrin-Zn(II) 29 [74], which was introduced in the former section of AND gates, becomes a representative NOR gate when 29 itself is viewed as a logic gate. Application of Ceo-appended imidazole 30 (inputA) bound it to the Zn(II) centre of 29 and set off a PET process from the porphyrin-Zn (II) unit to the Cgo moiety which switches the emission off [76]. Similarly, treatment of 29 with Cgo-attached ammonium ion 31 (inputB) bound the latter to the benzocrown ether of 29 and caused a PET process again [75]. The fluorescence was quenched as a result. Addition of both inputs formed a ternary complex 29/30/ 31 which was lumbered with two possible PET processes and no fluorescence was seen again. 

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