Inclusion compound

  In host-guest chemistry an inclusion compound is a complex in which one chemical compound the host forms a cavity which molecules of a second compound the guest are located. The definition of inclusion compounds is very broad, it extends to channels formed between molecules in a crystal lattice in which guest molecules can fit. If the spaces in the host lattice are enclosed on all sides so that the guest species is ‘trapped’ as in a cage, such compounds are known as clathrates. In molecular encapsulation a guest molecule is actually trapped inside another molecule.

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Cyclodextrin inclusion compounds

Inclusion complexes are formed between cyclodextrins and ferrocene^[1]. When a solution of both compounds in a 2:1 ratio in water is boiled for 2 days and then allowed to rest for 10 hours at room temperature orange-yellow crystals form. X-ray diffraction analysis of these crystals reveal a 4:5 inclusion complex with 4 molecules of ferrocene included in the cavity of 4 cyclodextrine molecules and with the fifth ferrocene molecule sandwiched between two stacks of ferrocene - cyclodextrine dimers.

Cyclodextrin also forms inclusion compounds with fragrance molecules^[2]. As a result the fragrance molecules have a reduced vapor pressure and are more stable towards exposure to light and air. When incorporated into textiles the fragrance lasts much longer due to the slow-release action.

References

• ^{^}  A unique tetramer of 4:5 -cyclodextrin–ferrocene in the solid state Yu Liu, Rui-Qin Zhong, Heng-Yi Zhang and Hai-Bin Song Chemical Communications, 2005, (17), 2211 - 2213 Abstract
• ^{^}  Fragrance-release Property of β-Cyclodextrin Inclusion Compounds and their Application in Aromatherapy C. X. Wang, Sh. L. Chen Journal of Industrial Textiles, Vol. 34, No. 3, 157-166 (2005) Abstract