2-electron-3-center bond
In a 2-electron-3-center bond , three atoms share an electron pair . This type of bond is found in only a few elements, e.g. B. Beryllium (second main group) and boron (third main group). They tend to form covalent bonds , have few valence electrons and thus do not achieve a complete electron octet . To saturate the valence, open 2-electron-3-center groupings therefore combine to form dimers or higher agglomerates. The concept of the 2-electron-3-center bond was developed by HC Longuet-Higgins in 1949 and expanded and refined by WN Lipscomb .
Bond Formation Theory
According to the molecular orbital theory , atomic orbitals are combined by linear combination of atomic orbitals. As a condition for the combination, the atomic orbitals must have comparable energies, overlap sufficiently spatially and have a suitable symmetry. In the 2-electron-3-center bond, three molecular orbitals are formed. One of these is always binding, one is always antibonding and the third is either non-binding or weakly binding or antibonding. The two electrons occupy the binding molecular orbital.
A distinction is made between open three-center bonds (bridge bonds ) and closed (centered) three-center bonds. A good example of three-center bonds can be found in the chemistry of boranes . A 2sp 3 orbital is involved in each of the boron atoms and, in the case of the open three-center bond, the 1s orbital of the hydrogen atom.
BHB three-center bond
Centered B, B, B three-center bond
Individual evidence
- ^ NN Greenwood, A. Earnshaw: Chemistry of the elements . VCH 1988, p. 199.
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 .