Triel bond and coordination of triel centres – Comparison with hydrogen bond interaction

Abstract

The triel bond may be defined as the interaction of the atom of 13th group that acts as the Lewis acid centre with the electron rich site of the species playing a role of the Lewis base. This interaction is often classified as the π-hole bond. Similar kinds of Lewis base sites occur for triel bonds and for hydrogen bonds. The following types of hydrogen bonds are discussed in different studies: A-H…B, A-H…π and A-H…σ interactions; A-H is the proton donating bond while B, π and σ mark a kind of proton acceptor: the mono-atomic Lewis base centre, the π-electrons and the σ-electrons, respectively. The triel centre, T, may also interact with such electron rich sites thus T…B, T…π and T…σ triel bonds may be identified. Different coordination of triel centres is discussed and corresponding examples of crystal structures taken from the Cambridge Structural Database are presented. The tetrahedral arrangements that obey the octet rule occur most frequently and they are characterised by the energetic stability. However trivalent and hypovalent triel structures that are characterised by the trigonal coordination as well as hypervalent triel structures possessing trigonal bipyramid and octahedral configurations occur in crystal structures frequently; other configurations are also discussed.