M…π(arene) interactions for M = gallium, indium and thallium: Influence upon supramolecular self-assembly and prevalence in some proteins

• Tl(lp)/Tl(III)…π(arene)/π(pyridyl) interactions are found in their molecular crystal structures.
• Synthons based upon points of contact based on Tl(lp)/Tl(III)…π(arene)/π(pyridyl) lead to supramolecular self-assembly.
• Zero-, one- and two-dimensional architectures may be stabilised by Tl(lp)/Tl(III)…π(arene)/π(pyridyl) interactions.
• Tl(lp)…π(arene) interactions are also found in some proteins.
• Ga(III), In(lp) and In(III)…π(arene) interactions are comparatively rare.

A bibliographic survey of the crystallographic literature reveals that Tl(lone pair)…π(arene) interactions, where the lone pair of electrons is projected plumb to the centre of the arene ring, occur in about 14% of molecular structures containing thallium(I) and an arene ring; similar Tl(lone pair)…π(arene) interactions are found in protein structures. Significantly smaller numbers of M(III)…π(arene), M = Ga, In and Tl, interactions were revealed. The Tl(lone pair)…π(arene) and related M(III)…π(arene), M = Ga, In and Tl, interactions are isolated from other obvious supramolecular synthons and provide clearly defined points of contact between molecules leading to zero-, one- and two-supramolecular aggregates in their crystal structures.