Pseudo-24-crown

Figure 5. Pseudo-crown ether phase transfer mechanism...

Molecular skeleton of the (UNUNj)4 ring in two crystalline polymorphs of [(C5Me5)2Uai-N)U(/i-N3)(C5Me5)2U pseudo-crown conformation observed for isomeric form A and pseudo-saddle observed for form B. The pair of r] -C5Me5 groups bonded to each uranium(IV) atom is not shown. From W. J. Evans, S. A. Kozimor and J. W. Ziller, Science 309, 1835-8 (2005). 

Ishida Y, Sasaki D, Miyauchi H et al (2(X)4) Design and synthesis of novel imidazolium-based ionic liquids with a pseudo crown-ether moiety diastereomeric interaction of a racemic ionic liquid with enantiopure europium complexes. Tetrahedron Lett 45 9455-9459... 

The reduction of electrical conductivity with time can serve as one line of evidence for complexation, as the highly mobile Na ion of the waterglass is localized by MGF-9 oxyethyleneglycol fragments that create pseudo-crown complexes. The same pattern is observed with introduction of dibenzo-18-crown-6 crown-ester into waterglasses with various silica moduli. 

The main obstacle to wide usage of crown-ethers in composition formulations is their comparatively high cost. One way of reducing costs is replacement of traditional crown-ethers with open-chain pseudo-crown-ethers. Furthermore, the use of crown-ethers allows the utilization for impregnation of very cheap monomers that may even be wastes from chemical production. 

Roncali, J., R. Garreau, and M. Lemaire. 1990. Electrosynthesis of conducting poly-pseudo-crown ethers from substituted thiophenes. J Electroanal Chem 278 373-378. 

The result of MGF-9 pseudo-crown complexation with waterglass sodium cations is a desolvated active hydroxyl ion whose initiating ability is considerably higher in the organo-mineral compositions investigated. Participation of phthalic, methacrylic, and carbamic adds, and sdicon-oxygen anions forms loose ion pairs with sodium cations whose activity in the cydotrimerization process is more than twofold higher [50, 94, 103]. 

Salen and additional Schiff base ligands complexing Cu ions are functionalized by pseudo-crowns , according to the authors definition. They are electropo-lymerized and identified as suitable to detect, by cyclic voltammetry, the occurrence of complexation with Ba(II) ions [121]. 

Binding of hard anions occurs strongly at the hard Lewis acidic uranyl center, whereas cation- tt interactions are established between the aromatic side arms and the cation counterpart of the ion pair. Thus, complexation of alkali metal salts (MX) such as CsCl and RbCl with 15 resulted in the formation of isomorphous supramolecular assemblies in the solid state. In the dimeric [15-CsCl], each cation is coordinated to six oxygens, three from each receptor, thus creating a pseudo-crown-ether-Uke environment for the cation. Additionally, each metal ion in the dimeric unit is coordinated to both halide ions and, most importantly, to two aromatic side arms, one from each of the receptors giving decacoordination for the cation. The closest metal ion-aromatic carbon distances of 3.44(1) A for CsCl, 3.34-3.38(1) A for RbCl, and 3.58(1) A for CsF are observed in the respective alkali halide complexes [15 MX] indicating the conformational flexibility of the side arms and adaptability of the receptors 15 and 16 to form multiple cation- rt interactions with the hosted cations. 

Fig. 10. Electrofoimation of pseudo-crown ether cavities containing materials according to a two-step anodic route.

A novel strategy for forming controlled-size pseudo-crown ethers from acyclic polyethers has recently been proposed by Fabre et al. [258]. As conceptualized in Fig. 10, it consisted of the electrosynthesis of electroactive copolymers from compounds possessing two different electropolymerizable aromatic groups (pyr-role/thiophene (10), pyrrole/dimethoxybenzene (11), and thio-phene/dimethoxybenzene (12)) linked together by a polyether chain. 

Because of possible ion-selective effects, pseudo-crown ethers were prepared by electropolymerization from suitably substituted thiophenes by Roncali et al. [1093]. The polymer formed from l,14-(3-thienyl)-3,6,9,12-tetraoxatetradecane showed an absorption maximum at A = 430 nm in the undoped state. Compared to the respective value for poly(3-(3,6,9-trioxade( l))thiophene, a blue shift of about SO nm, indicating a shorter mean conjugation length, was found. In the oxidized form, this band was considerably reduced in intensity, and a new band at A = 750 nm, attributed to a transition into the upper bipolaron band, was seen. The results were found to be inferior to those of polymers prepared from 3-polyether-substituted monomers. A general review of this field was provided by Fabre and Simonet [1094] for further details, see also [1095]. 

This approach has been extended to the synthesis of macrocyclic ethers (pseudo-crown ethers) incorporated as part of a macromolecular network (styrene-divinylbenzene copolymer) and results in polymers of high coordinating power for various ions (139). The combination of macrocyclic structures with polymer will allow, in the near future, the development of new catalysts containing specific binding properties together with effective catalytic behavior (348). 

Polymeric pseudo-crown ether (139). Reprinted with permission. Copyright 1979 by the American Chemical Society. 

The polyoxyethylene portion of nonionic surfactants forms pseudo-crown compounds in the presence of barium ions which can be titrated with sodium tetraphe-nylborate using the Orion surfactant electrode as an end-point indicator electrode. An average recovery of 96.4 % can obtained for the determination of three standard detergents. The described method has been used successfully in the routine determination of nonionic surfactants. 

The diffusion, location and interactions of guests in zeolite frameworks has been studied by in-situ Raman spectroscopy and Raman microscopy. For example, the location and orientation of crown ethers used as templates in the synthesis of faujasite polymorphs has been studied in the framework they helped to form [4.297]. Polarized Raman spectra of p-nitroaniline molecules adsorbed in the channels of AIPO4-5 molecular sieves revealed their physical state and orientation - molecules within the channels formed either a phase of head-to-tail chains similar to that in the solid crystalline substance, with a characteristic 0J3 band at 1282 cm , or a second phase, which is characterized by a similarly strong band around 1295 cm . This second phase consisted of weakly interacting molecules in a pseudo-quinonoid state similar to that of molten p-nitroaniline [4.298]. 

Supplement A The chemistry of double-bonded functional groups (2 parts) Supplement B The chemistry of acid derivatives (2 parts) Supplement C The chemistry of triple-bonded functional groups (2 parts) Supplement D The chemistry of halides, pseudo-halides and azides (2 parts) Supplement E The chemistry of ethers, crown ethers, hydroxyl groups and their sulphur analogues (2 parts)... 

Supplement D The Chemistry of Halides, Pseudo-halides and Azides (two parts) Supplement E The Chemistry of Ethers, Crown Ethers, Hydroxyl Groups and their Sulphur Analogues (two parts)... 

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