The re-entrant phase transitions in crystalline malononitrile, CH2(CN)2: a neutron powder diffraction study
The temperature dependence of the crystal structures of the low-temperature α-phase and the intermediate-temperature β-phase of crystalline malononitrile, CH2(CN)2, have been determined using Rietveld refinement on neutron powder diffraction data. The results confirm that the α-phase has the same structure as the high-temperature γ-phase, and the refined structure of the β-phase is in agreement with previous structure determination using single-crystal x-ray diffraction. The variations of the structure with temperature due to the phase transitions are identified and analysed in terms of molecular rotations and spontaneous strains.
Observation of a re-entrant phase transition in the molecular complex tris(μ2-3,5-diisopropyl-1,2,4-triazolato-κ2 N 1:N 2)trigold(I) under high pressure
Single-crystal crystallography shows that one polytype of the AuI trimer tris(μ2-3,5-diisopropyl-1,2,4-triazolato-κ2 N 1:N 2)trigold(I), [Au3(N3C8H14)3], undergoes four successive phase transitions between 1 and 3.5 GPa, driven by aurophilic interactions, and that the ambient-pressure structure re-emerges at high pressure.
Vibration spectra and force constants of malononitrile, malononitrile-d1 and malononitrile-d2
Abstract The infrared and Raman spectra of malononitrile, and its deuterium compounds were measured. The normal frequencies and modes of NCCH 2 CN, NCCHDCN and NCCD 2 CN were calculated on the basis of the Urey—Bradley force field. Assignments of vibrational bands were made. All the skeletal deformation bands were explained. The transferability of force constants was also discussed.