Chemists in the UK and Italy have made halogen-bonded liquid crystals that they say have an unusually disordered structure. 

Duncan Bruce at the University of York, Giuseppe Resnati and Pierangelo Metrangolo at the Politecnico di Milano and colleagues mixed highly-fluorinated iodo-compounds with amino-containing molecules, neither of which show liquid crystalline behaviour on their own. Over certain temperature ranges, the compounds reorganised to form chains.  The chains formed a disordered liquid crystal phase held together by halogen bonds.

Halogen bonds are analogous to hydrogen bonds. They are based on the interaction between an electron-poor halogen, such as iodine, and an electron-rich Lewis base, such as an amine. 

According to Bruce, fluorinated compounds usually increase the ordering of chains within a liquid crystal. Bruce had previously made a highly-ordered liquid crystal phase by combining iodo- and amino-compounds in a one-to-one ratio. But when the researchers used the compounds in a two-to-one ratio a more random chain arrangement was formed.

The scientists say they are currently unable to explain the findings but they are continuing to investigate the unusual behaviour. According to Bruce, the subtle nature of the intramolecular interactions will ensure a challenge. However, the potential for exciting, novel liquid crystalline materials is 'extremely enticing,' said Bruce.

Paul O'Sullivan