Temperature dependent order–disorder multiple phase transitions studies of the hexamethylenetetraminium p-nitrobenzoate crystal

Acta Crystallogr Sect B

2017

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Hexamethylenetetramine-benzoic acid (1/2) (HBA) and hexamethylenetetramine-4-methylbenzoic acid (1/2) (HMBA) co-crystals undergo order-disorder structural phase transition from a low-temperature monoclinic crystal structure to a high-temperature orthorhombic crystal structure at the transition temperatures of 257.5 (5) K (Pn ↔ Fmm2) and 265.5 (5) K (P2/n ↔ Cmcm), respectively, using variable-temperature single-crystal X-ray diffraction analysis. The observed phase transitions were confirmed to be reversible first-order transitions as indicated by the sharp endothermic and exothermic peaks in the differential scanning calorimetry measurement. The three-molecule aggregate of HBA and HMBA consists of a hexamethylenetetramine molecule and two benzoic acid or two 4-methylbenzoic acid molecules, respectively. The acid molecules are ordered at the low-temperature phase and are equally disordered over two positions, which are related by a mirror symmetry, at the high-temperature phase. The two-dimensional supramolecular constructs common to both co-crystals are formed by three-molecule aggregates via weak intermolecular C-H...O and C-H...π interactions into molecular trilayers parallel to the ac plane with small XPac dissimilarity indices and parameters. The PIXEL interaction energies of all corresponding molecular contacts were calculated and the results are comparable between HBA and HMBA co-crystals, resulting in similar lattice energies and transition temperatures despite their two-dimensional isostructural relationship. The observed phase transitions of these two energetically similar co-crystals are triggered by similar mechanisms, i.e. the molecular rotator ordering and structural order-disorder transformation, which induced non-merohedral twinning with similar twin matrices in the low-temperature crystal form of both co-crystals.

Section: Introductionmentioning

confidence: 99%

Temperature-induced order–disorder structural phase transitions of two-dimensional isostructural hexamethylenetetramine co-crystals

Acta Crystallogr Sect B

2017

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“…The temperature-or pressure-induced phase transitions are accompanied with different types of structural changes such as displacive (Zhang et al, 2013;Rybarczyk-Pirek et al, 2014), order-disorder (Wu & Jin, 2013;Suzuki et al, 2014;Brandel et al, 2015), reconstructive (Johnston et al, 2014;Maloney et al, 2014) etc. The high-temperature phase of an enantiotropic phase transition in a crystal is commonly of higher symmetry than its low-temperature phase; however, an isosymmetry transition with the same space-group symmetry at both phases does exist (Swainson et al, 2002 Quah et al, 2012;Ellena et al, 2014). m-Carboxyphenylammonium monohydrogenphosphite (Bendeif et al, 2005(Bendeif et al, , 2009) is a phosphite salt which exhibits a first-order displacive-type isosymmetry (monoclinic, P2 1 /c $ P2 1 /c) structural phase transition at 246 K, induced by rotation and translation of both cations and anions in the crystal, leading to competition between intra-and intermolecular interactions.…”

Section: Introductionmentioning

confidence: 99%

Temperature-induced first-order displacive phase transition of isonicotinamide-4-methoxybenzoic acid co-crystal

Acta Crystallogr Sect B

2017

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Isonicotinamide-4-methoxybenzoic acid co-crystal (1), CHNO·CHO, is formed through slow evaporation from methanol solution and it undergoes a first-order isosymmetry (monoclinic I2/a ↔ monoclinic I2/a) structural phase transition at T = 142.5 (5) K, which has been confirmed by an abrupt jump of crystallographic interaxial angle β from variable-temperature single-crystal XRD and small heat hysteresis (6.25 K) in differential scanning calorimetry measurement. The three-dimensional X-ray crystal structures of (1) at the low-temperature phase (LTP) (100, 140 and 142 K) and the high-temperature phase (HTP) (143, 150, 200, 250 and 300 K) were solved and refined as a simple non-disordered model with final R[F > 2σ(F)] ≃ 0.05. The asymmetric unit of (1) consists of crystallographically independent 4-methoxybenzoic acid (A) and isonicotinamide (B) molecules in both enantiotropic phases. Molecule A adopts a `near-hydroxyl' conformation in which the hydroxyl and methoxy groups are positioned on the same side. Both `near-hydroxyl' and `near-carbonyl' molecular conformations possess minimum conformational energies with an energy difference of < 0.15 kJ mol from a potential energy surface scan. In the crystal, molecules are joined into linear ABBA arrays by intermolecular N-H...O and O-H...N hydrogen bonds which were preserved in both phases. However, these ABBA arrays are displaced from planarity upon LTP-to-HTP transition and the changes in inter-array interactions are observed in two-dimensional fingerprint plots of their Hirshfeld surfaces. The PIXEL energies of each molecular pair in both phases were calculated to investigate the difference in intermolecular interaction energies before and after the displacement of ABBA arrays from planarity, which directly leads to the single-crystal-to-single-crystal phase transition of (1).

“…A search in the Cambridge Structural Database (CSD; Version 5.37; Groom et al, 2016) for 2-methylbenzoic acid revealed three polymorphs (Katayama et al, 1967;Thakur & Desiraju, 2008;Polito et al, 2008;Fronczek, 2014). Conformational flexibility in the crystalline state may contribute to an order-disorder phase transition in which different conformers co-exist in the high-temperature form and are transformed into a single stable conformer in the low-temperature form upon cooling; this transformation may or may not be associated with a change in the space group (Quah et al, 2012). Temperatureinduced translationengleiche group-subgroup relations such as the monoclinic-to-orthorhombic phase transition observed in barbituric acid dihydrate (P2 1 /n $ Pnma) (Nichol & Clegg, 2005) and Boc-4 (R)Val-Val-OH crystals (P2 1 $ P22 1 2 1 ) (Pal et al, 2014) result in twinned crystals, whereas klassengleichetype phase transitions associated with loss of translational symmetry will produce antiphase domains (Mü ller, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…Pseudomerohedral twins are often encountered in monoclinic crystal structures when either the angle is close to 90 or the lattice parameters a and c are similar and the angle is close to 120 (Mü ller et al, 2006;Parsons, 2003). To date, three cocrystals of hexamethylenetetramine and substituted benzoic acids (Chantrapromma et al, 2006;Fun et al, 2007;Quah et al, 2012) have been reported to exhibit reversible phase transitions. In this work, variable-temperature single-crystal X-ray diffraction and differential scanning calorimetry were employed to investigate the temperature-dependent monoclinic-to-orthorhombic phase transition of the hexamethylenetetramine-2-methylbenzoic acid (1/2) cocrystal, (I).…”

Section: Introductionmentioning

confidence: 99%

Monoclinic-to-orthorhombic phase transition of the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal with temperature-dependent dynamic molecular disorder

2016

Acta Crystallogr C

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As a function of temperature, the hexamethylenetetramine-2-methylbenzoic acid (1/2) cocrystal, CHN·2CHO, undergoes a reversible structural phase transition. The orthorhombic high-temperature phase in the space group Pccn has been studied in the temperature range between 165 and 300 K. At 164 K, a t phase transition to the monoclinic subgroup P2/c space group occurs; the resulting twinned low-temperature phase was investigated in the temperature range between 164 and 100 K. The domains in the pseudomerohedral twin are related by a twofold rotation corresponding to the matrix (100/0-10/00-1. Systematic absence violations represent a sensitive criterium for the decision about the correct space-group assignment at each temperature. The fractional volume contributions of the minor twin domain in the low-temperature phase increases in the order 0.259 (2) → 0.318 (2) → 0.336 (2) → 0.341 (3) as the temperature increases in the order 150 → 160 → 163 → 164 K. The transformation occurs between the nonpolar point group mmm and the nonpolar point group 2/m, and corresponds to a ferroelastic transition or to a t structural phase transition. The asymmetric unit of the low-temperature phase consists of two hexamethylenetetramine molecules and four molecules of 2-methylbenzoic acid; it is smaller by a factor of 2 in the high-temperature phase and contains two half molecules of hexamethylenetetramine, which sit across twofold axes, and two molecules of the organic acid. In both phases, the hexamethylenetetramine residue and two benzoic acid molecules form a three-molecule aggregate; the low-temperature phase contains two of these aggregates in general positions, whereas they are situated on a crystallographic twofold axis in the high-temperature phase. In both phases, one of these three-molecule aggregates is disordered. For this disordered unit, the ratio between the major and minor conformer increases upon cooling from 0.567 (7):0.433 (7) at 170 K via 0.674 (6):0.326 (6) and 0.808 (5):0.192 (5) at 160 K to 0.803 (6):0.197 (6) and 0.900 (4):0.100 (4) at 150 K, indicating temperature-dependent dynamic molecular disorder. Even upon further cooling to 100 K, the disorder is retained in principle, albeit with very low site occupancies for the minor conformer.