Structural and Thermodynamic Insight into Solid State Phase Transition Mechanism of a 1,3,3′-Triketone

A study of a solid state phase transition in dipivaloyl­(3-cyclopentylpropanoyl)­methane was undertaken by a combination of crystallographic and calorimetric methods. The high temperature polymorph with two molecules in the asymmetric unit and a disordered cyclopentyl group undergoes a reversible phase transition into an ordered structure with a single molecule in the asymmetric unit. The transition temperature is −20.80 °C with a minimal hysteresis of 1 °C. The nucleation of the new phase was followed by differential scanning calorimetry and occurs in a wide temperature range starting from ca. 0.5 °C above and below the transition temperature, and the crystallographic orientation of the crystals of the nascent phase is to a high degree in agreement with that of the parent crystal.