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The polymorphism of 1,3-dimethyladamantane (13DMA), 1,3-adamantanediol (13DOHA) and 1,3-dibromoadamantane (13DBrA) has been studied by X-ray powder diffraction, density measurements and differential scanning calorimetry at normal and high-pressure. 13DMA exhibits a low-temperature ordered monoclinic phase (space group P21/c, Z = 4, Z′ = 1) which transforms at 222.6 ± 0.5 K into a high-temperature hexagonal plastic phase (P63/mmc, Z = 26), stable up to the melting point at 246.8 ± 0.5 K at normal pressure. 13DOHA exhibits a low-temperature hexagonal phase (P63/mcm, Z = 6, Z′ = 0.25) which transforms into a face-centered cubic plastic phase (Fm3¯m). 13DBrA exhibits a unique ordered orthorhombic phase (Pnma, Z = 4, Z′ = 0.5) which remains till the melting point at 382.1 ± 0.5 K. The stability temperature domain of the plastic phases increases with pressure for both 13DMA and 13DOHA. The ability to form the plastic phase for these compounds as well as a series of adamantanes derivatives is analysed through the globularity and asphericity parameters derived from the Hirshfeld surface analysis. [ABSTRACT FROM AUTHOR]

The formation of co-crystals is often unexpected; however, the Buckminster fullerene, for which many solvates are known, is an excellent system to study this tendency. In the present paper, C60 and CBrCl2H solvates have been studied. Hexagonal P6/mmm C60·2CBrCl2H solvates transform at 373 K to monoclinic C2/c C60·CBrCl2H solvates. While orientational disorder typical for C60 is found in the hexagonal solvates (as found in many C60 halomethane solvates), in the monoclinic solvates, C60 appears to be orientationally ordered. As for the solvent CBrCl2H, two types of occupational disorder involving the distribution of the halogen atoms can be observed, comparable to the behaviour in the two polymorphs of pure CBrCl2H. Within the monoclinic solvate, two sites are equally occupied by Br and Cl atoms (1/2 : 1/2), while one site is fully occupied by a Cl atom which leads to an average Cs symmetry for the solvent molecule. Whereas within the hexagonal solvates, each halogen position is occupied by 1/3 : 2/3 of Br or Cl atoms, respectively, leading to an average C3v molecular symmetry. The anisotropy of the intermolecular interactions coincides with the symmetry of the solvate structures and can be generalized for the C60·halomethane solvates. [ABSTRACT FROM AUTHOR]

The co-crystal of C60·2CBrClH2 possesses a monoclinic (C2/m) structure at room temperature with both molecular entities, C60 and CBrClH2, orientationally ordered. At 322 K, it transforms reversibly into a hexagonal (P6/mmm) setting, revealing a rare example of a heteromolecular stator–rotator transition in a fullerene co-crystal, which applies to both the fullerene and the coformer analogous to the paradigmatic C60–cubane co-crystal. However, in the present case, topological molecular surface matching between the two chemical species is not necessary and the order–disorder phase transition reflects simultaneous activation of the orientational disorder of both C60 and CBrClH2. [ABSTRACT FROM AUTHOR]

The co-crystal of C60·2CBrClH2 possesses a monoclinic (C2/m) structure at room temperature with both molecular entities, C60 and CBrClH2, orientationally ordered. At 322 K, it transforms reversibly into a hexagonal (P6/mmm) setting, revealing a rare example of a heteromolecular stator–rotator transition in a fullerene co-crystal, which applies to both the fullerene and the coformer analogous to the paradigmatic C60–cubane co-crystal. However, in the present case, topological molecular surface matching between the two chemical species is not necessary and the order–disorder phase transition reflects simultaneous activation of the orientational disorder of both C60 and CBrClH2. [ABSTRACT FROM AUTHOR]

In the case of small organic molecules, phase behaviour, which is important for pharmaceutical applications, is often only studied as a function of temperature. However, for a full thermodynamic description, not only the temperature but also the pressure should be taken into account, because pressure and temperature are the two characteristic variables for the Gibbs energy. The commercial form of l-tyrosine ethyl ester has been studied by synchrotron X-ray diffraction while subjected to different pressures and temperatures. At room temperature, it turns into a new previously unknown form around 0.45 GPa. The structure has been solved with an orthorhombic unit cell, space group P212121, with parameters a = 12.655(4) Å, b = 16.057(4) Å, c = 5.2046(12) Å, and V = 1057.6(5) Å3 at T = 323 K and P = 0.58 GPa. The enthalpy of the transition from the commercial form to the new form could be estimated from the slope of the transition obtained from the synchrotron diffraction data. In addition, the topological pressure–temperature phase diagram has been constructed involving the two solid phases, the liquid and the vapour phase. The solid phases are enantiotropic under low pressure, but the system becomes monotropic at high pressure with the new solid phase being the only stable one. [ABSTRACT FROM AUTHOR]

Correction for 'Polymorphism and solid–solid phase transitions of hydrogen bonded 2-adamantanol and 2-methyl-2-adamantanol compounds' by Alejandro Salvatori et al., CrystEngComm, 2022, 24, 3692–3700, https://doi.org/10.1039/D2CE00324D. [ABSTRACT FROM AUTHOR]