Tetrabromobenzene-based molecular alloys – a tool for tailoring the temperature of the thermosalient phase transition†

Abstract

A series of molecular alloys of 1,2,4,5-tetrabromobenzene and 1,2,4,5-tetrachlorobenzene with varying compositions were prepared in an attempt to obtain jumping crystals with adjustable temperature of thermosalient phase transition. Molecular alloys were studied with a combination of thermal and structural techniques (DSC, SCXRD, XRPD, hot-stage microscopy). Alloys with a high 1,2,4,5-tetrabromobenzene content (more than 90 wt%) exhibited thermosalient behaviour. Thermosalient alloys exhibited negative uniaxial thermal expansion and colossally large coefficients of thermal expansion (both linear and volumetric), with unit cell parameters increasing proportionally with tetrabromobenzene content. Finally, it was found that the temperature of phase transition increases linearly with the tetrabromobenzene content, from 30.13 °C to 45.33 °C, meaning that the tuning temperature of thermosalient mechanic response was successfully achieved.