A temperature‐induced order–disorder phase transition in a 4‐substituted 4, 2′:6′, 4′′‐terpyridine. Issue 6 (1st December 2015)

• Record Type: Journal Article
• Authors: Granifo, Juan; Westermeyer, Marleen; Riquelme, Maricel; Gaviño, Rubén; Suárez, Sebastián; Halac, Emilia B.; Baggio, Ricardo
• Is Part Of: Acta crystallographica. Volume 71:Issue 6(2015:Dec.)
• Page Start: 805
• Page End: 813
• Publication Date: 2015-12-01
• Subjects: phase transition -- first order -- ligand properties -- weak interactions -- order–disorder
• DOI: 10.1107/S205252061501937X
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : Crystals of 4′‐(isoquinolin‐4‐yl)‐4, 2′:6′, 4′′‐terpyridine ( iqtp ), C24 H16 N4, grown from an ethanol solution, undergo a reversible first‐order single‐crystal to single‐crystal phase transition at T c in the range 273–275 K, from a disordered higher‐temperature phase [form (I)] in the space group P 21 / c, with one single molecule in the asymmetric unit, to an ordered lower‐temperature one [form (II)] in the space group P 21 / n, with two independent molecules in the asymmetric unit. There is a group–subgroup relationship linking (I)–(II), due to cell doubling and the disappearance of a number of symmetry operations. In addition to X‐ray diffraction, the transition has been monitored by Raman spectroscopy and differential scanning calorimetry, the latter disclosing an enthalpy change of 0.72 (6) kJ mol −1 . Variations of the unit‐cell parameters with temperature between 170 and 293 K are presented. The evolution of diffraction spots in the vicinity of the transition temperature shows the coexistence of both phases, confirming the first‐order character of the transition. Structural details of both phases are analyzed and intermolecular interactions compared in order to investigate the mechanism of the phase transition. A three‐dimensional Hirshfeld surface analysis was performed to corroborate the significant changes in the intermolecular features.