What is Macrobicyclic effect?
What is Macrobicyclic effect?
The results are interpreted in terms of the macrobicyclic cryptate effect: for cations small enough to fit inside the cryptand, the three-dimensional preorganization of the ligand leads to stronger binding than is possible for a floppier, pseudo-two-dimensional crown ether.
What is cryptate chemistry?
noun. Chemistry. A coordination complex in which a metal cation is bound within a cavity in the molecule of a cryptand.
What are cryptands give example?
For example, addition of 2,2,2-cryptand to a solution of sodium in ammonia affords the salt [Na(2,2,2-crypt)]+e−, isolated a blue-black paramagnetic solid. Cryptands have also been used in the crystallization of Zintl ions such as Sn 4− 9.
What is kryptofix?
8]hexacosane (Kryptofix 2.2. 2) is used in the routine preparation of [18F]-labeled tracers employed in positron emission tomography (PET) imaging. Confirming the absence of Kryptofix in radiopharmaceuticals is a quality control criterion required before they can be released for human use.
What is meant by Nephelauxetic effect?
The nephelauxetic effect is a term used in the inorganic chemistry of transition metals. It refers to a decrease in the Racah interelectronic repulsion parameter, given the symbol B, that occurs when a transition-metal free ion forms a complex with ligands.
What are Cryptates and cryptands?
Cryptands are macrobicyclic, macrotricyclic, etc. compounds generally having nitrogen atoms at the bridgehead positions, having sufficient space within its cage structure for polydentate ligation to metal ions or other cationic species; the resulting complexes are called cryptates.
What is crown ether complex?
Crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups. Crown ethers strongly bind certain cations, forming complexes. The oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of the ring is hydrophobic.
What are Podands?
podand (plural podands) (organic chemistry) Any open-chain equivalent of a crown ether, i.e. a compound having one or more -O-CH2-CH2-O- group.
What is Paracyclophane?
In ‘[6]paracyclophane’ which is one of the smallest, yet stable, cyclophanes X-ray crystallography shows that the aromatic bridgehead carbon atom makes an angle of 20.5° with the plane. The benzyl carbons deviate by another 20.2°. The carbon-to-carbon bond length alternation has increased from 0 for benzene to 39 pm.
What is a Corand?
Corand (10 mg) is a vasodilator, prescribed for angina pectoris (chest pain).
What is nephelauxetic effect example?
What kind of complex does a cryptand form?
The complex between the cationic guest and the cryptand is called a cryptate. Cryptands form complexes with many “hard cations” including NH+ 4, lanthanoids, alkali metals, and alkaline earth metals. In contrast to crown ethers, cryptands bind the guest ions using both nitrogen and oxygen donors.
How does macrobicyclic cryptate affect complexation selectivity?
This effect was termed the macrobicyclic cryptate effect, by analogy to the macrocyclic effect. As with crown ethers, the complexation selectivity of the cryptands can be altered by varying the size of the cavity defined by the ligand.
What are the hard cations of a cryptand?
Cryptands form complexes with many “hard cations” including NH +. 4, lanthanoids, alkali metals, and alkaline earth metals. In contrast to crown ethers, cryptands bind the guest ions using both nitrogen and oxygen donors.
How are cryptands used in the real world?
Although more expensive and more difficult to prepare than crown ethers, cryptands bind alkali metals more strongly. They are especially used to isolate salts of highly basic anions. They convert solvated alkali metal cations into lipophilic cations, thereby conferring solubility in organic solvents to the resulting salts.
