The potential to control distances between the aromatic rings of molecules in the solid state has been studied by materials scientists in Spain and Finland.

Clara Viñas and co-workers from the Insitute de Ciencia de Material De Barcelona, Spain and the Universities of Jyväskylä and Helsinki, Finland, synthesised substituted benzene rings with two, four and six pyrrolylmethyl arms. They analysed the arrangements and bond distances in the crystal structures to investigate the interactions between different parts of the molecules.

Viñas found that the di- and tetra-substituted rings displayed C-H··· interactions between the pyrrolylmethyl arm of one molecule and the arene ring of another. The orientation of the pyrrolyl groups in the hexa-substituted benzene blocked the face of the aromatic ring and therefore 'switched off' both ?-stacking and C-H··· interactions. 

The understanding of molecular interactions (for example, hydrogen bonds or - bonds) is of great importance in the development of new functional materials. These forces have a strong influence over the three-dimensional architectures displayed in crystal structures and their control is of key importance to crystal engineers.

The implications of this C-H··· interaction concept will open up a wide range of possibilities in the design of new drugs and materials with potential applications in industry, technology and medicine.

Richard Kelly