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.