Cryptates

cryptate is one of type of macrocyclic ligand. please note there are typing mistakes in the introduction discovering year is 1968.

1. Inorganic chemistry CRYPTATSE By , T.DEEPA M.sc chemistry 1 st yr

2. INTRODUCTION CRYPTATSE also known as CRYPTAND. Cryptand were discovered by French Chemists Jean-Marie lehn in 1987. This French chemists got Noble prize for Chemistry [Discovering &Determining uses] of cryptatse in 1987. Cryptand is poly ,di & macrocyclic ligand giving rise to different shape of complexes based on ethereal oxygen donor atom.

3. Structure of cryptatse Cryptand word refer to crypt –internal cavity ,intramolecular cavity & hidden. and represent ligand. Cryptand bi or tricyclic or multicyclic can provide the cage structure to accommodate the metal ion &other guest species. The cavity size to wrap around or hide alkali cation of different sizes ,with difference strength of complexation . Cryptates are more potent ,selective & even stronger complexing agent for alkali metal . And also show high & low complexing ability metal ion of alkaline earth metal ,a few transition & lanthanides ions. Here cryptand are nitrogenous macrocyclic compound with 3- dimensional intramolecular cavities.

4. The molecules are appropriately cross linked with donor atom [ethereal oxygen] correctly positioned in the bridging group [N-N] to encapsulate metal ion like a cage structure. Basic structure of cryptand is crypt [222]. which is also known has football ligand. Chemical formula for cryptand [222] is N[CH2 CH2 O CH2 CH2 CH2 O CH2 CH2]3N 222 is a denotes ethereal oxygen atom. Bridged form structure

5. This image represent synthesis of cryptand in the presence of sutiable alkali metal ion like k+. This ligand is a very high formation of complexes constants. OCTOPUS LIGANDS Marocycles polydentate ligands are not only for production stable alkali complexes. Additional conformational flexibility without loss of coordinating power can be achieved with 2-6 pendant mercapto -polyether group C6H6-nRn where R is –SC2H4OC2H4Me,-S[C2H4O]3Bu etc. This ligand are called octopus ligands are more effective as crypt sequestering [form chelate or other compound & used to prevent chemical effect of an ion without removing it from the solution ] alkali metal cation.

6. PROPERTIES COMPLEXES WITH ALKALI METALS The stability of complexes with common ligands were low & generally found to decrease In the sequence. Li > Na > K > Rb > Cs The ligands shows selectively among alkalies in forming complexes. It form stable complexes with alkali cation and other metal cation. It survive definitely in aqueous solution as well. For crypt [222] K+ is appropriate to fit in the cavity. But Li+, Na+ are too small Rb+, Cs+ are too big to form stable complexes. In crypt 211,221 & another type of ligands [octopus ligands] however, form their most stable complexes with Li+ & Na+.

7. The stability depends upon : Size of the metal ion. Number ethereal oxygen. Geometric diposition of ethereal oxygen atom. Size & shape of the macrocycle.

8. 2] ANIONIC CRYPT cationic crypt has dominated in its complexes with alkali & a few other metal cation for a long time. Likewise ,anionic crypt have also come into existence. Polyamine – based cryptands can be converted to polyammonium cages. Which exhibit high affinities for anions .

9. 3] SEPULCHRATES A group of multicyclic encapsulating ligands called sepulchrates are closely related to football ligands . This are synthesized around a metal ion which cannot be released. Sepulchrates are stable over PH ranges which makes easier the investigation of solution chemistry of elements Mo ,W . Which are tendency to hydrolysis & polymerization by changes in PH.

10. 4] SIZE The cavity diameter of cryptands increase with increasing no: of oxygen donor sites. It is evident that for Li+, Na+, K+, the most stable cryptands [211], [221] ,[222]. 5] OTHER PROPERTIES This complexes resulting lipophilic. Some cryptands are lumiscent .

11. APPLICATIONS Cryptand are used to preparative organic chemistry Solvent extraction Phase transfer catalysis Reactive oxidation states Solubility of alkali metals salts in organic media can be promoted crypts due to presence of hydrophobic organic ring in the ligand . Eg:KOH & KMno4 can be used an alkali an oxidizing agent . ZINTL SALTS : A number of zintl salts [containing alkali metal cation & zintl anions ] Been prepared with the help crypt in anhydrous solvent . Crypt, the study is not yet complrte . It’s also used for biochemical process involving metal ions. Cryptand is used to study a new concept supramolecular chemistry entirely. Cryptand enabled the synthesis of the alkalides & electrides Many cryptand are commercially available under the trade name kryptofix .

12. Thank you