Alkali metals Group cryptands

Solid-liquid phase-transfer catalyst.1 The reagent represents a new class of catalysts, acyclic cryptands or tridents. It is singled out of a group as the best compromise of efficiency/price/toxicity. It solubilizes salts of alkali metals as well as of transition metals such as RuC13 and PdCl2, probably because of the flexibility of the molecule. In addition the trident is sensitive to the nature of the anion, but anionic activation is less than that obtained with cryptands. 

Obviously, many structural variations are possible in the design of ferrocene oxa-aza cryptands. Some of the oxa-azaferrocene cryptands form alkali metal and lanthanide complexes [90]. FAB mass spectrometry experiments have shown that the cryptands have strong selectivity for the potassium cation compared with Li+, Na, or Cs" " [94], In these complexes the macrocycle functions as a host, but in Mg + complexes the cation is coordinated by the amide carbonyl groups [95]. In the lanthanide complexes the metallocene moiety acts as an efficient center for radiationless deactivation of the lanthanide excited state [96]. 

Because of their structures the ferrocene aza-oxa cryptands, 45, can simultaneously bind anions by interaction with the ferrocene CO-NH group (with hydro-gen-bonding participation) and alkali metal ions (in the crown ether moiety) [92]. 

Alkali metal anions have been known to exist in the gas phase for over 30 years, and they have been proposed as major contributing species in metal-ammonia solutions since 1965 (53,54). By using cryptand C222, Dye and his corworkers were able in 1974 to isolate and to characterize fully—including an X-ray structure—a crystalline salt of the sodium anion Na , in which the counterion is the sodium cation Na" " spirited away within the cavity of the cryptand (55,56). The Dye group has since prepared analogous crystalline solids for all the other alkali metals" except lithium, and mixed systems in which the... 

Cryptands are cyclic (mainly) polyether molecules with usually three chains linked at nitrogen caps at each end of the molecule (Figure 4.42), much like the sarcophagines but with a different capping atom and different donors. They can, depending on host cavity size, bind metal ions (alkali or alkaline earth ions preferred) or small molecules. A wide range of molecules of this family have been prepared. They can be effective in metal ion selection from a group of ions, useful in both analysis and separation of mixtures. They also help solubilize metal ions in aprotic solvents. 

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