Crown ethers with lanthanides

The interaction between the simple crown ethers with lanthanide ions is weak in water. However, in non-aqueous media, the interaction is stronger, which allows one to form and isolate complexes. The stoichiometry of the crown ether coronates depends upon several factors the relative size of the ligand cavity and the ionic diameter, the nature... 

Columnar phases could also be obtained by reacting disk-shaped molecules such as crown ethers with lanthanide salts. BiinzU and coworkers reported, for example, the preparation of thermotropic hexagonal columnar phases from nonmesogenic crown ethers and several different ions of the lanthanide family [76], An additional property of these compounds is a metal-centered emission, in the case of the liquid-crystalline phases containing Eu and Tb, making them attractive for the design of luminescent liquid-crystalline materials [76],... 

Complexes of alcohols like methanol, ethanol, 2-propanol and n-butanol (116-122), and ethers like Diox (47,120,123-125) and THF (126-128) have been prepared. The bonding between these ligands and the metal ions is considered to be very weak. In recent years, complexes of the lanthanides with a few macrocyclic polyethers have been reported. Cassol et al. (129) have prepared the complexes of benzo-15-crown-5 and dibenzo-18-crown-6 with lanthanide nitrates and isothiocyanates. King and Heckley (130) have also reported the complexes of these ligands with lanthanide nitrates. The heavier lanthanide nitrate complexes of dibenzo-18-crown-6... 

With respect to heavier lanthanide ions such as Ybm, 15-crown-5 has the most adequate cavity size (Btinzli and Pilloud, 1989) and Korovin has fitted this crown ether with an anili-noacridine chromophore which displays cytostatic and/or antiviral activity. If anilinoacridines alone, bearing a hydroxyl or a carboxylic acid substituent in ortho, meta, or para position (fig. 23), are reacted with ytterbium trinitrate, they yield 1 1 complexes with the ortho- and... 

The decomplexation of trivalent lanthanide complexes of l,10-diaza-4,7,13,16-tetraoxacyclooctadecane-JV-acetic acid (K22MA) and l,10-diaza-4,7,13,16-tet-raoxacyclooctadecane-iV,N -di-i3-propionic acid (K22DP) (which are diaza crown ethers with one and two carboxylic acid pendant arms attached to the diaza nitrogens, respectively) has been studied by a spectrophotometric SF method, and is characterized by the rate law (64). When the diaza crown ether is K22MA, fcd = 0.88, 0.25, and 3.99 s respectively, for La ", Eu, and Lu and -1.42 X lO and 4.93 x 10 dm moP s for La and Eu and when the diaza... 

Various crown ethers (p. 96) with differing cavity diameters provide a range of coordination numbers and stoichiometries, although crystallographic data are sparse. An interesting series, illustrating the dependence of coordination number on cationic radius and ligand cavity diameter, is provided by the complexes formed by the lanthanide nitrates and the 18-crown-6 ether (i.e. 1,4,7,10,13,16-... 

NMR investigation of molecular structure of paramagnetic lanthanide complexes with crown ethers in solutions 98ZSK714. 

In a different approach three different structurally defined aza-crown ethers were treated with 10 different metal salts in a spatially addressable format in a 96-well microtiter plate, producing 40 catalysts, which were tested in the hydrolysis of /xnitrophenol esters.32 A plate reader was used to assess catalyst activity. A cobalt complex turned out to be the best catalyst. Higher diversity is potentially possible, but this would require an efficient synthetic strategy. This research was extended to include lanthanide-based catalysts in the hydrolysis of phospho-esters of DNA.33... 

Liu, Y., Zhang, H. Y., Bai, X. P., Wada, T., and Inoue, Y. (2000) Molecular design of crown ethers. 21. Synthesis of novel double-armed benzo-15-crown-5 lariats and their complexation thermodynamics with light lanthanoid nitrates in acetonitrile, J. Org. Chem. 65, 7105-7109 see also Danil de Namor, A. F. D., Chahine, S., Jafou, O., and Baron, K. (2003) Solution thermodynamics of lanthanide-cryptand 222 complexation processes, J. Coord. Chem 56, 1245-1255 Israeli, Y., Bonal, C., Detellier, C., Morel, J. P., and Morel-Desrosiers, N. (2002) Complexation of the La(III) cation by p-sulfonatocalix[4]arene - A La-139 NMR study, Canad. J. Chem. 80, 163-168. 

Wai, C. M. (1997) Separation of lanthanides and actinides with ionizable crown ethers, Recent Progress in Actinides Separation Chemistry, Proceedings of the Workshop on Actinides Solution Chemistry, WASC 94, Tokai, Japan, Sept. 1-2, 1994, 81-94. 

Meguro, Y., Kitatsuji, Y., Kimura, T., and Yoshida, Z. (1995) Separation factors in synergistic ion-pair extraction of lanthanide(III) with crown ether and b-diketone, Kidorui, 26, 380-381. 

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. 

On their own polyethers have had limited use in supramolecular chemistry. Low molecular mass compounds have been shown to bind a number of metal ions, notably those in the lanthanide series that can accommodate ligands with large numbers of oxygen donor atoms. One of the main problems is the lack of diversity in the compounds functional groups which limits the range of their ligating opportunities. Where polyethers have been highly successful is as substituents to other molecules, such as calixarenes, and in their cyclic forms as the crown ethers, which will be described later. 

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