Acta Crystallographica Section B

Structural Science

Volume 62, Part 6 (December 2006)

research papers

Acta Cryst. (2006). B62, 1078-1089 [ doi:10.1107/S010876810602982X ]

Competing hydrogen-bonding patterns and phase transitions of 1,2-diaminoethane at varied temperature and pressure

A. Budzianowski, A. Olejniczak and A. Katrusiak

Abstract: 1,2-Diaminoethane has been in-situ pressure- and temperature-frozen; apart from two known low-temperature phases, I [alpha] and II, three new phases, I [beta] , I [gamma] and III, have been observed and their structures determined by X-ray diffraction. The measurements at 0.1 MPa were carried out at 274, 243 and 224 K, and 296 K measurements were made at 0.15 GPa (phase I [alpha] ), at 0.3 and 1.1 GPa (phase I [beta] ), at 1.5 GPa (phase I [gamma] ), 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 [alpha] and III are very different at 296 K: a_I = 5.078 (5), b_I = 7.204 (8), c_I = 5.528 (20) Å, _I = 115.2 (2)° at 0.15 GPa, and a_III = 5.10 (3), b_III = 5.212 (2), c_III = 7.262 (12) Å, _III = 111.6 (4)° at 0.2 GPa, respectively; in both phases Z = 2. An ambient-pressure low-temperature phase II has been observed below 189 K. Discontinuities in the unit-cell dimensions and in the NN distance mark the isostructural transition between phases I [alpha] and I [beta] at 0.2 GPa, which can be attributed to a damping process of the NH₂ group rotations. In phase I [gamma] 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.

Keywords: N-HN hydrogen-bonds; molecular conformations; intermolecular interactions; phase transitions; molecular dynamics; high pressure; molecular aggregation; crystallization; structural transformations; separation by freezing.


	Structure factor file (CIF format) (14.5 kbytes) [ doi:10.1107/S010876810602982X/av5066dae015gsup2.hkl ] Contains datablock DAE015G

	Structure factor file (CIF format) (9.4 kbytes) [ doi:10.1107/S010876810602982X/av5066dae02gsup3.hkl ] Contains datablock DAE02G

	Structure factor file (CIF format) (6.7 kbytes) [ doi:10.1107/S010876810602982X/av5066dae03g1sup4.hkl ] Contains datablock DAE03G1

	Structure factor file (CIF format) (8.0 kbytes) [ doi:10.1107/S010876810602982X/av5066dae03g2sup5.hkl ] Contains datablock DAE03G2

	Structure factor file (CIF format) (13.4 kbytes) [ doi:10.1107/S010876810602982X/av5066dae05gsup6.hkl ] Contains datablock DAE05G

	Structure factor file (CIF format) (8.4 kbytes) [ doi:10.1107/S010876810602982X/av5066dae11gsup7.hkl ] Contains datablock DAE11G

	Structure factor file (CIF format) (15.2 kbytes) [ doi:10.1107/S010876810602982X/av5066dae15gsup8.hkl ] Contains datablock DAE15G

	Structure factor file (CIF format) (28.9 kbytes) [ doi:10.1107/S010876810602982X/av5066dae224ksup9.hkl ] Contains datablock DAE224K

	Structure factor file (CIF format) (28.9 kbytes) [ doi:10.1107/S010876810602982X/av5066dae243ksup10.hkl ] Contains datablock DAE243K

	Structure factor file (CIF format) (28.6 kbytes) [ doi:10.1107/S010876810602982X/av5066dae274ksup11.hkl ] Contains datablock DAE274K

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