On the propulsion mechanism of "jumping" crystalsElectronic supplementary information (ESI) available: Experimental details including DSC and crystal tables; crystallographic information files (.cif); video of crystal response to cooling and heating. CCDC 951477-951482. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3cc45646c

A crystalline metal-organic complex undergoes a polymorphic transformation upon cooling below 215 K. Depending on the cooling rate, crystals exhibit different behaviours that include breaking and "jumping". Variable temperature X-ray diffraction (XRD) and optical microscopy have been employed to analyze the anisotropic changes of the crystallographic axes and propose a mechanism by which the crystals acquire the momentum for the jump. A crystalline metal-organic complex undergoes a polymorphic transformation upon cooling below 215 K. Depending on the cooling rate, crystals exhibit different behaviours that include breaking and "jumping". Variable temperature X-ray diffraction (XRD) and optical microscopy have been employed to analyze the anisotropic changes of the crystallographic axes and propose a mechanism by which the crystals acquire the momentum for the jump.