15-Crown-5 Explained

15-Crown-5 is a crown ether with the formula (C2H4O)5. It is a cyclic pentamer of ethylene oxide that forms complex with various cations, including sodium (Na+)[1] and potassium (K+);[2] however, it is complementary to Na+ and thus has a higher selectivity for Na+ ions.

Synthesis

15-Crown-5 can be synthesized using a modified Williamson ether synthesis:[3]

(CH2OCH2CH2Cl)2 + O(CH2CH2OH)2 + 2 NaOH → (CH2CH2O)5 + 2 NaCl + 2 H2O

It also forms from the cyclic oligomerization of ethylene oxide in the presence of gaseous boron trifluoride.

Properties

Analogous to 18-crown-6, 15-crown-5 binds to sodium ions. Thus, when treated with this complexing agent, sodium salts often become soluble in organic solvents.

First-row transition metal dications fit snugly inside the cavity of 15-crown-5. They are too small to be included in 18-crown-6. The binding of transition metal cations results in multiple hydrogen-bonded interactions from both equatorial and axial aqua ligands, such that highly crystalline solid-state supramolecular polymers can be isolated. Metal salts isolated in this form include Co(ClO4)2, Ni(ClO4)2, Cu(ClO4)2, and Zn(ClO4)2. Seven coordinate species are most common for transition metal complexes of 15-crown-5, with the crown ether occupying the equatorial plane, along with 2 axial aqua ligands.[4]

15-crown-5 has also been used to isolate salts of oxonium ions. For example, from a solution of tetrachloroauric acid, the oxonium ion has been isolated as the salt . Neutron diffraction studies revealed a sandwich structure, which shows a chain of water with remarkably long O-H bond (1.12 Å) in the acidic proton, but with a very short OH•••O distance (1.32 Å).

A derivative of 15-crown-5, benzo-15-crown-5, has been used to produce anionic complexes of carbido ligands as their salts:

See also

Further reading

External links

Notes and References

  1. A Conductance Study of 1:1 Complexes of 15-Crown-5, 16-Crown-5, and Benzo-15-crown-5 with Alkali Metal Ions in Nonaqueous Solvents . Takeda, Y. . Bulletin of the Chemical Society of Japan . 1988 . 61 . 3 . 627–632 . 10.1246/bcsj.61.627. etal. free .
  2. Potassium ion recognition by 15-crown-5 functionalized CdSe/ZnS quantum dots in H2O . Chen, Chun-Yen . Chem. Comm. . 2006 . 263–265. 10.1039/B512677K. 3. 16391728 . etal.
  3. Cook. Fred L.. Caruso. Thomas C.. Byrne. Michael P.. Bowers. Chauncey W.. Speck. Don H.. Liotta. Charles L.. 1974. Facile syntheses of 12-crown-4 and 15-crown-5. Tetrahedron Letters. en. 15. 46. 4029–4032. 10.1016/S0040-4039(01)92075-1.
  4. Book: Supramolecular Chemistry, 2nd edition. Jonathan W. Steed. Jerry L. Atwood. Wiley. 2009. 978-0-470-51233-3.