Structure of [2. 2. 2]cryptand encapsulating a potassium cation (purple). At crystalline state, obtained with an X-ray diffraction. ^[1]

Cryptands are a family of synthetic bi- and polycyclic multidentate ligands for a variety of cations. In Chemistry, a ligand is either an Atom, Ion, or Molecule (see also Functional group) that bonds to a central metal generally ^[2] The Nobel Prize for Chemistry in 1987 was given to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen for their efforts in discovering and determining uses of cryptands and crown ethers, thus launching the now flourishing field of supramolecular chemistry. Donald James Cram (April 22 1919 &ndash June 17 2001 was an American chemist who shared the 1987 Nobel Prize in Chemistry with Jean-Marie Jean-Marie Lehn (born September 30, 1939) is a French Chemist. Charles John Pedersen ( October 3, 1904 &ndash October 26, 1989) was an American organic chemist best known for describing Crown ethers are heterocyclic Chemical compounds that consist of a ring containing several Ether groups Supramolecular chemistry refers to the area of Chemistry that focuses on the Noncovalent bonding interactions of molecules ^[3] The term cryptand implies that this ligand binds substrates in a crypt, interring the guest as in a burial. In terms of European architecture a crypt (from the Latin crypta and the Greek κρυπτη, kryptē) is a stone chamber or These molecules are three dimensional analogues of crown ethers but are more selective and complex the guest ions more strongly. Crown ethers are heterocyclic Chemical compounds that consist of a ring containing several Ether groups The resulting complexes are lipophilic.

Structure

The most common and most important cryptand is N[CH₂CH₂OCH₂CH₂OCH₂CH₂]₃N; the formal IUPAC (International Union of Pure and Applied Chemistry) name for this compound is 1,10-diaza-4,7,13,16,21,24-hexaoxabicyclo[8. The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization 8. 8]hexacosane. So it is easy to see why the common name of "cryptand" was preferable. This compound is termed [2. 2. 2]cryptand, where the numbers indicate the number of ether oxygen atoms (and hence binding sites) in each of the three bridges between the amine nitrogen "caps". Many cryptands are commercially available under the tradename "Kryptofix. " All-amine cryptands exhibit particularly high affinity for alkali metal cations, which has allowed the isolation of salts of K^-. ^[4]

Properties

The three-dimensional interior cavity of a cryptand provides a binding site - or nook - for "guest" ions. The complex between the cationic guest and the cryptand is called a cryptate. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Cryptands form complexes with many "hard cations" including NH₄⁺, lanthanoids, alkali metals, and alkaline earth metals. Terminology The Trivial name " Rare earths " is sometimes used to describe all the lanthanoids together with Scandium and Yttrium In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal Biological occurrences Beryllium's low aqueous solubility means it is rarely available to biological systems it has no known role in living organisms and when encountered In contrast to typical crown ethers, cryptands bind the guest ions using both nitrogen and oxygen donors. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Their three-dimensional encapsulation mode confers some size-selectivity, enabling discrimination among alkali metal cations (e. g. Na⁺ vs. K⁺).

Uses

Cryptands although they are more expensive and more difficult to prepare offer much better selectivity and strength of binding^[5] than other complexants for alkali metals, such as crown ethers. Crown ethers are heterocyclic Chemical compounds that consist of a ring containing several Ether groups They are able to extract otherwise insoluble salts into organic solvents. They can be also be used as phase transfer catalysts by transferring ions from one phase to another. A phase transfer catalyst or PTC in Chemistry is a Catalyst which facilitates the migration of a reactant in a Heterogeneous system from one ^[6] Cryptands enabled the synthesis of the alkalides and electrides. An electride is an ionic compound in which an Electron is the Anion. They have also been used in the crystallization of Zintl ions such as Sn₉²⁻. In Chemistry, a cluster is an ensemble of bound Atoms intermediate in size between a Molecule and a bulk Solid.

References

1. ^ Alberto, R. ; Ortner, K. ; Wheatley, N. ; Schibli, R. ; Schubiger, A. P. "Synthesis and properties of boranocarbonate: a convenient in situ CO source for the aqueous preparation of [^99mTc(OH₂)₃(CO)₃]⁺. " J. Am. Chem. Soc. 2001, 121, 3135-3136. doi:10.1021/ja003932b
2. ^ von Zelewsky, A. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. Stereochemistry of Coordination Compounds; John Wiley: Chichester, 1995. ISBN 0-471-95057-2.
3. ^ Lehn, J. M. Supramolecular Chemistry: Concepts and Perspectives; VCH: Weinhiem, 1995.
4. ^ Kim, J. ; Ichimura, A. S. ; Huang, R. H. ; Redko, M. ; Phillips, R. C. ; Jackson, J. E. ; Dye, J. L. "Crystalline Salts of Na⁻ and K⁻ (Alkalides) that Are Stable at Room Temperature. " J. Am. Chem. Soc. 1999, 121, 10666–10667. doi:10.1021/ja992667v
5. ^ Dietrich, B. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. "Cryptands" in Comprehensive Supramolecular Chemistry; Gokel, G. W. Ed; Elsevier: Oxford, 1996; Vol. 1, pp 153–211. ISBN 0080406106.
6. ^ Landini, D. ; Maia, A. ; Montanari, F. ; Tundo, P. "Lipophilic [2. 2. 2] cryptands as phase-transfer catalysts. Activation and nucleophilicity of anions in aqueous-organic two-phase systems and in organic solvents of low polarity. " J. Am. Chem. Soc. 1979, 101, 2526–2530. doi:10.1021/ja00504a004

General reading

Lee, J. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. D. (1991). Concise Inorganic Chemistry, 4th edition, New York: Chapman & Hall, 306-08 & 353. ISBN 0-412-40290-4.