Co-crystal of suberic acid and 1,2-bis(4-pyridyl)ethane:A new case of packing polymorphism

The polymorphic behaviour of a co-crystal composed of neutral suberic acid and 1,2-bis(4-pyridyl)ethane is reported. A multidisciplinary approach has been employed, using thermal analysis methods (differential scanning calorimetry and polarized light thermomicroscopy), spectroscopic methods (infrared spectroscopy) and X-ray single crystal and powder diffraction. Two new polymorphs, Land III; have been identified, and for one of them the crystal structure has been elucidated and compared to that of a known polymorph, form II, showing that the assembling of the molecules in chains via H-bonds is a common feature of both polymorphs. Polymorph II, obtained by crystallization from an aqueous or ethanol solution or by grinding, undergoes a solid-solid transition to polyniorph I, which melts at 180.5 degrees C. Upon cooling from the melt, polymorph I is obtained, and a solid-solid transformation also occurs, to poly morph III'. Polymorph III was obtained serendipitously in an attempt to prepare a Nd(III) complex. The relative stability of the three polymorphic forms was established. (C) 2017 Elsevier B.V. All rights reserved.