Andrzej Katrusiak, Armand Budzianowski, Kamil Dziubek
Armand Budzianowski Anna Olejniczak and Andrzej Katrusiak
1,2-Diaminoethane has been in-situ pressure- and temperature-frozen; apart from two known low-temperature phases, I and II, three new phases, I, I and III, have been observed and their structures determined by X-ray diffraction. The measurements at 0.1MPa were carried out at 274, 243 and 224K, and 296K measurements were made at 0.15GPa (phase I), at 0.3 and 1.1GPa (phase I), at 1.5GPa (phase I), and at 0.2, 0.3 and 0.5 GPa (phase III). All these phases are monoclinic, space group P21/c, but the unit-cell dimension of phases I and III are very different at 296 K: aI=5.078(5), bI=7.204(8), cI=5.528(20)Å, I=115.2(2)° at 0.15GPa, and aIII=5.10(3), bIII=5.212 (2), cIII=7.262 (12)Å, III = 111.6(4)° at 0.2GPa, respectively; in both phases Z=2. An ambient-pressure low-temperature phase II has been observed below 189K. Discontinuities in the unit-cell dimensions and in the NN distance mark the isostructural transition between phases I and I at 0.2GPa, which can be attributed to a damping process of the NH2 group rotations. In phase I the unit-cell parameter a doubles and Z increases to 4. The molecule has inversion symmetry in all the structures determined. 1,2-Diaminoethane can be considered as a simple structural ice analogue, but with NHN hydrogen bonds and with the H-atom donors (four in one molecule) in excess over H-atom acceptors (two per molecule). Thus, the transformations of 1,2-diaminoethane phases involving the conformational dynamics affect the hydrogen-bonding geometry and molecular association in the crystal. The 1,2-diaminoethane:1,2-dihydroxyethane mixture has been separated by pressure-freezing, and a solid 1,2-diaminoethane crystal in liquid 1,2-dihyroxyethane has been obtained.
Anna Olejniczak, Michalina Anioła, Marek Szafrański, Armand Budzianowski and Andrzej Katrusiak
Andrzej Katrusiak, Marcin Podsiadło and Armand Budzianowski
Armand Budzianowski and Andrzej Katrusiak
Acta Crystallographica Section B
Volume 62, Part 1 (February 2006)
Acta Cryst. (2006). B62, 94-101 [doi:10.1107/S010876810503747X]
Authorised by IUCr electronic reprint of the article
The crystal structure of benzene, C6H6, in situ pressure-frozen in phase I, has been determined by X-ray diffraction at 0.30, 0.70 and 1.10GPa, and 296K. The molecular aggregation within phase I is consistent with van der Waals contacts and electrostatic attraction of the positive net atomic charges at the H atoms with the negative net charges of the C atoms. The C-Haromatic ring centre contacts are the most prominent feature of the two experimentaly determined benzene crystal structures in phases I and III, whereas no stacking of the molecules has been observed. This specific crystal packing is a likely reason for the exceptionally high polymerization pressure of benzene. The changes of molecular arrangement within phase I on elevating the pressure and lowering the temperature are analogous.