Cryptand

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Structure of [2.2.2]cryptand encapsulating a potassium cation (purple). At crystalline state, obtained with an X-ray diffraction.[1]
[2.2.2]Cryptand

In

lipophilic.[4]

Structure

The most common and most important cryptand is N[CH2CH2OCH2CH2OCH2CH2]3N; the systematic

K−.[6]

Properties

Cation binding

The three-dimensional interior cavity of a cryptand provides

alkaline earth metals. In contrast to crown ethers, cryptands bind the guest ions using both nitrogen and oxygen donors. This three-dimensional encapsulation mode confers some size-selectivity, enabling discrimination among alkali metal cations (e.g. Na+ vs. K+). Some cryptands are luminescent.[7]

Anion binding

Polyamine-based cryptands can be converted to polyammonium cages, which exhibit high affinities for anions. [8]

Laboratory uses

Cryptands enjoy some commercial applications (e.g. in homogenous-time-resolved-fluorescence, HTRF, technologies using Eu3+ as central ion). More importantly, they are reagents for the synthesis of inorganic and organometallic salts. Although more expensive and more difficult to prepare than crown ethers, cryptands bind alkali metals more strongly.[9] They are especially used to isolate salts of highly basic anions.[10] They convert solvated alkali metal cations into lipophilic cations, thereby conferring solubility in organic solvents to the resulting salts.

Referring to achievements that have been recognized in textbooks, cryptands enabled the synthesis of the

Zintl ions such as Sn4−
9.[13]

Although rarely practical, cryptands can serve as

phase transfer catalysts since their cationic complexes are lipophilic.[14]

See also

References

  1. PMID 11457025
    .
  2. ISBN 0-471-95057-2
    .
  3. ^ Lehn, J. M. (1995). Supramolecular Chemistry: Concepts and Perspectives. Weinheim: VCH.
  4. PMID 25138490
    .
  5. ^ 23978-09-8
  6. doi:10.1021/ja992667v
    .
  7. doi:10.1016/S0010-8545(00)00246-0
    .
  8. S2CID 22334242
    .
  9. doi:10.1039/F19858102495
    .
  10. ISBN 0-08-040610-6
    .
  11. S2CID 93768664
    .
  12. ISBN 0-12-352651-5
  13. doi:10.1021/ic50170a036
    .
  14. doi:10.1021/ja00504a004
    .

General reading
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