A temperature-induced order–disorder phase transition in a 4-substituted 4,2′:6′,4′′-terpyridine

Abstract

Crystals of 4'-(isoquinolin-4-yl)-4,2':6',4''-terpyridine (iqtp), C24H16N4, grown from an ethanol solution, undergo a reversible first-order single-crystal to single-crystal phase transition at Tc in the range 273-275 K, from a disordered higher-temperature phase [form (I)] in the space group P21/c, with one single molecule in the asymmetric unit, to an ordered lower-temperature one [form (II)] in the space group P21/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.

Dinuclear complexes of Mn, Co, Zn and Cd assembled with 1,4-cyclohexanedicarboxylate: synthesis, crystal structures and acetonitrile fluorescence sensing properties

“…The reported Cd(II) heptacoordinated complexes exhibit similar bond length values. [41][42][43] Due to the noticeable differences in distances and the corresponding angles that give form to the trapezoid and triangular faces, in the distorted-monocapped trigonal prismatic geometry of Cd(II) in 4, the two triangular faces are not parallel (Fig. S5, ESI †).…”

Spironolactone: New Polymorphic Form III and Revisiting Form II at Low Temperatures

“…37 Comparable order−disorder transitions that occur in conjunction with temperature-dependent conformational changes can be found in the literature, sometimes being described as phase transitions, 38 and sometimes not. 39 Interestingly, this phenomenon can cause changes in the material, for example exhibiting second-order nonlinear optical properties as the consequence of symmetry loss below a certain temperature. 40…”

“…Given the ongoing discussion about the classification of polymorphs of organic molecules, we were reluctant to classify this behavior as a phase transition but rather regard this a low-temperature modification of form II . , This is especially the case as the found geometries clearly represent only conformational adjustments against proper changes, this means the conformers do not represent separated local minima on the potential energy surface . Comparable order–disorder transitions that occur in conjunction with temperature-dependent conformational changes can be found in the literature, sometimes being described as phase transitions, and sometimes not . Interestingly, this phenomenon can cause changes in the material, for example exhibiting second-order nonlinear optical properties as the consequence of symmetry loss below a certain temperature …”

The enrichment ratio of atomic contacts in the crystal structure of isomeric, triply protonated, 4′-functionalized terpyridine cations with [ZnCl4]2− as counter-ion

“…Now, given that protonation leads to an increase on the positive charge in the C atoms and that the negative charge of the N atoms is almost invariant, a natural conclusion is that this ought to enrich the cationic CÁ Á ÁN interactions. In an attempt to explore the effect of the position of the protonated N atoms on this type of interaction, we decided to protonate the already known isomeric base 4 0 -(isoquinolin-4-yl)-4,2 0 :6 0 ,4 00 -terpyridine (44TP) (Granifo et al, 2015) and to study the crystal structure of the new related compound (44TPH 3 ) 2 [ZnCl 4 ] 3 (I). Fig.…”

“…The tetrachloridozincate salt (44TPH 3 ) 2 [ZnCl 4 ] 3 was prepared by the reaction of 4 0 -(isoquinolin-4-yl)-4,2 0 :6 0 ,4 00 -terpyridine (44TP; Granifo et al, 2015), ZnCl 2 and concentrated HCl (37%). 44TP (4.8 mg) was placed in a small beaker and dissolved with concentrated HCl (0.5 ml) and then 0.5 ml of water was added.…”