Alkali complexes

During the past few decades, it has been shown that multi-nuclear NMR is a very powerful experimental technique to study alkali complexes particularly in non-aqueous solutions. The experimental method used throughout this work was 7Li NMR. This method possesses features that make it convenient for this kind of investigation. Particular attention was given to high-pressure 7Li NMR, which includes the first example reported for... 

MD simulations performed on calix[4]arene-monocrown-6 and on calix[4]arene-bis-crown-6 and their alkali complexes, suggested that incorporation of aromatic groups in the crown ether loop was a possible way to enhance cation binding and cesium over sodium selectivity.45... 

Results obtained by ES/MS confirm that the stability of calixarene/cation complexes depends upon the medium. The calixarene in solution presents a strong affinity for cesium, whereas in the gas phase, it displays a stronger affinity for sodium. Moreover, the stability of calixarene/Na+ complexation in a solvent phase is increased by the presence of water in the dilution system (up to 40% in acetonitrile), whereas other alkali complexes are destabilized by the presence of water. Finally, affinity for sodium, which is weak in the solution for calixarenes bearing benzo moieties, considerably increases in the gas phase. These results confirm the interpretation of the MD simulations in an aqueous phase, which lead the authors to conclude that cesium-over-sodium selectivity is governed by the hydration of the sodium cation in the complex, and by the higher hydrophobicity of the complexation site leading to an enhancement of selectivity for cesium over sodium 49... 

Wipff, G., Weiner, P., Kollman, P. A. (1982), A Molecular Mechanics Study of 18-Crown-6 and Its Alkali Complexes An Analysis of Structural Flexibility, Ligand Specificity, and the Macrocyclic Effect, J. Am. Chem. Soc. 104, 3249-3258 and refs cited therein. 

While however neither its triethylammonium salt nor its alkali salts are stable in solution, the salts of crown ether-alkali complexes are stable as such and in solution. 

This preorganization principle not only affects the thermodynamic stability of the complex but also has a pronounced effect on the kinetic stability of the alkali complexes of the spherands. The anisyl groups in the spherands provide the preorganized ligating donor sites, and they shield the cavity from solvent molecules. As a result, the rates of complexation by the spherands are decreased and the rates of decomplexation are decreased even more when compared with related flexible crown ethers. 

Crown Ether - Alkali Complexes Questioning the Best-fit Model... 

The stability constants of the alkali complexes — and even more so for the far better studied alkaline earth complexes (72) — do not show any uniform dependence on the radius of the metal ions (cf. Fig. 7). Any simple model would have to correspond to a monotonic decrease in the... 

A molecular mechanics study of 18-crown-6 and its alkali complexes - an analysis of structural flexibility, ligand specificity, and the macrocyclic effect, G. Wipff, P. Weiner and P. Kollman, J. Am. Chem. Soc., 1982, 104, 3249. 

Both hydrolysis and composition of a hydroxo complex turn out to be dependent on the solutions pH values. Some metals (Fe, Cr, AP, Hg + and some others) are capable of hydrolysis at low pH, some others (Pb +, Cu +, Ni +, Zn + and some others) - at pH 6 and higher, and the fraction of their hydroxides increases with the growth of pH. The result is the formation of acidic, neutral or alkali complexes like MeOHp, Me(OH) and Me(OH)p respectively. 

Jedlinski, Z., Novel Electron-Transfer Reactions Medialed by Alkali Complexed by Macrocyclic Ligand. Accounts of Chem. Res. 31 55-61... 

The productivity of a well depends on the surface of salt available to the injected water. Productivity in a new well is very low, but as the cavity grows it increases to the design rate. In opening a new field, it takes some time to reach full production. This is an important consideration in the startup of a new brine/chlor-alkali complex. The rate of solution of salt increases when the flow of dissolving fluid is turbulent, but this improvement in rate may be offset by a decrease in the concentration of salt in the finished brine. When a new well is brought on line in an operating field, weak startup brine can go to a mature well for saturation, and startup is more efficient. 

The covalent behaviour - of alkali derivatives of the Zr2(OPr )9 ligand in fact initiated an interest in the chemistry of such heterometallic alkoxides, at a time when such covalent complexes as [Cs Y(CF3COCHCOCF3)4 ] and [K Sc(CF3COCHCOCF3)4 ] were quoted as rare examples of covalent alkali complexes in an article by Nyholm et al ... 

R. Ferrara, B.E. Maserti, H. Edner, P. Ragnarson, S. Svanberg, E. Wal-Under Mercury emi ions into the atmosphere from a chlor-alkali complex measm ed with the lidar technique. Atmos. Environ. 26A, 1253 (1992)... 

Morf, W. E., and Simon, W., Thermodynamic parameters of the ring compounds-alkali complexes in aqueous solvent, Helv. Chim. Acta, 54, 794, 1971. 

Maserti BE, Ferrara R (1991) Mercury in plants, soil and atmosphere near a chlor-alkali complex. Water Air Soil Pollut 56(1) 15-20. doi 10.1007/bf00342257... 

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