Metal ions cesium complexes

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... 

But it was not to be. Try as we might, the difference in scattering lengths between the 6Li and 7Li isotopes was too small to permit us to measure the lithium ion distribution in the swollen state. We had to content ourselves with the results for the crystalline phase, where the behavior of the lithium ions is different from that of the larger alkali metal cations [27], Potassium and cesium ions bind directly to vermiculite clay surfaces rather than hydrating fully. Because only lithium-substituted vermiculites of the alkali metal series will swell macroscopically when soaked in water, it seems that interlayer cations must form fully hydrated ion-water complexes if the particles are to expand colloidally. This conclusion has since been supported... 

D. Whang, J. Heo, J.H. Park, K. Kim, A Molecular Bowl with Metal Ion as Bottom Reversible Inclusion of Organic Molecules in Cesium Ion Complexed Cucurbituril , Angew. Chem. Int. Ed., 37,78 (1998)... 

In contrast to conventional cation exchangers, a reversed elution order is observed with crown ether phases, which is mainly determined by the size ratio between crown ether ring and alkali metal ion. Due to the high affinity of poly(benzo-15-crown-5) toward potassium and rubidium ions, these are more strongly retained than lithium, sodium, and cesium ions, respectively. However, the complexing properties of crown ethers also depend on the counter ion being employed. Thus, in potassium salts, for example, an increase in retention in the order KC1 < KBr < KI is observed with an increasing size of the counter ion. 

It must be stressed that factors such as the hydration (or solvation) of the metal ion and anion effects on the extracted complex often make it difficult to predict the order of extractability for such systems. Such factors may even influence the stoichiometry of the extracted species. Thus, the simple match of the metal to the whole concept is only of limited utility. For example, potassium, rubidium and sodium nitrates are extracted in the presence of dibenzo-18-crown-6 (2) as 1 1 1 complexes. On the other hand, cesium forms a 1 2 1 sandwich complex with this crown (metal crown nitrate) in the organic phase and this affects the extraction order for the above metal ions, with the order being dependent on ligand concentration. In contrast, for picrate as the anion the composition of the extracted cesium complex is 1 1 1 (Fig. 4.8) [27]. 

Analytical chemistry of the alkalis is difficult. There are a few complex reagents that will precipitate with ions like Na+ and K+, but the reactions are best done using ether or alcohol as the solvent in place of water. It is more common to detect the presence of alkali metals in solutions or compounds by the characteristic colors the alkali metal ions impart to flames. In descending order, lithium salts give a carmine color, sodium salts a yellow color, potassium a violet color, rubidium a bluish red color, and cesium a blue color. 

In the [2.2.2] complex with cesium, the Cs" ". .. O distances are somewhat smaller than the corresponding sum of the Van-der-Waals radius of oxygen and the ionic radius of Cs", as was similarly observed in the Cs" complex of nonactin (see Chap. 3). This indicates that the cation presses heavily on the ligand. In fact, it was concluded from Cs-NMR data that in solution, [2.2.2] forms an exclusive complex with Cs" ", i.e. the metal ion does not occupy the central ligand cavity but is only partly... 

Whang D, Heo J, Park JH, Kim K. A molecular bowl with metal ion as bottom reversible inclusion of organic molecules in cesium ion complexed cucurbituril. Angew Chem Int Ed... 

The complexes formed between Cu(II) ions and a number of D-aldonic and D-alduronic acids in aqueous solution has been studied, and the complex obtained from methyl a-D-mannopyranoside and copper(II) hydroxide in the presence of lithium hydroxide has been identified as the square planar structure 17. The determination of stability constants of Ca complexes with /wyo-inositol 1,4,5-trisphosphate is discussed in Chapter 18. The interaction of L-ascorbic acid with some metal ions has b n studied in aqueous solution at pH 6-7, and the solid hydrated salts lithium, sodium, potassium, ammcHiium, rubidium and cesium ascorbate have been isolated and characterised by C n.m.r. and f.t.ix. spectroscopy... 

---