Electron donor acceptor complexes

Electron donor acceptor complexes , often abbreviated as EDA complexes , are complexes that are addition products of an electron donor and an electron acceptor . In the scientific literature, there is often no distinction between electron donor acceptor complexes and charge transfer complexes ( CT complexes for short ). However, some authors differentiate that in CT complexes, charge transfer actually takes place, which is only a special case for EDA complexes. Thus only a part of all EDA complexes are also CT complexes.

Ferrocene is an example of an electron donor acceptor complex with a metal ion as acceptor and two aromatics as π donors

The electron pair provided by the donor molecule in the EDA complex can either be a free electron pair (n-donor) or an electron pair from a double bond or an aromatic system (π-donor). Evidence of the presence of an EDA complex is provided by the electronic spectrum : so-called charge transfer bands appear there that are not present in any of the individual spectra of the starting compounds of the complex.

EDA complexes can be divided into the following categories:

• Complexes with a metal ion as acceptor and an olefin or aromatic as π-donor, e.g. B. ferrocene
• Complexes with an organic molecule as acceptor (the most common example of this is picric acid and other similarly structured nitroaromatics , but also quinones or tetracyanoethylene ) and a π donor (e.g. aromatics, amines or alkenes )
• Complexes with a halogen element as acceptor and amines, aromatics, alcohols, ketones and the like. a. as a donor. An example of this is the color of a solution of iodine in benzene or acetone that deviates from the iodine color .

EDA complexes are often colored, some are unstable and can only exist in solution in equilibrium with the starting components, others are stable crystalline solids. The stoichiometric composition is often 1: 1, but complexes with a stoichiometric composition are also known.

See also

• Charge transfer complexes
• Crown ether

Individual evidence

1. ↑ Jerry March: Advanced Organic Chemistry. Wiley Interscience, New York 1997, ISBN 3-528-06657-1 , p. 115 ( limited preview in Google book search).