Cryptands are a class of chemical compounds that have a unique structure capable of encapsulating metal ions or other small molecules. They contain three or more coordinating groups arranged in a cyclic structure, which can form a cavity that is perfectly suited to host specific guest molecules.
Cryptands are known for their high selectivity and affinity towards certain metal ions, making them useful in various applications such as ion separation, catalysis, and molecular recognition.

Properties of Alkali Metals
- Reactivity: Alkali metals are highly reactive due to their low ionization energy, which allows them to easily lose their outermost electron to form positively charged ions.
- Softness: Alkali metals are soft and can be easily cut with a knife. This is due to their low melting points and weak metallic bonding.
- Low Density: Alkali metals have low densities compared to other metals, which makes them float on water.
- High Thermal Conductivity: Alkali metals have high thermal conductivity, making them useful in heat transfer applications.
- Flame Test: Alkali metals exhibit characteristic flame colors when burned, such as lithium (red), sodium (yellow), and potassium (violet).
Overall, alkali metals exhibit unique properties that make them important elements in various fields of science and technology.

Cryptands belongs to the family of bicyclic and polycyclic multidentive ligands.