Structural phase transitions in malononitrile

Abstract

Previous studies using nuclear quadrupole resonance and calorimetric methods have shown that there are two second-order phase transitions in malononitrile at 141 and 294.7 K and that the low-and high-temperature phases have the same symmetry. In this paper the crystal structure of the intermediate phase is reported and compared with a previous determination of the high-temperature phase. The unit cell dimensions of the two structures are almost identical and the space groups are

Polymorphism of malononitrile. Crystallographic characterization of theL–Fphase transition

“…The F phase has been reported as monoclinic (P21; a=7.82, b= 7.63, c=6.16/~ and fl=96.7 ° at 287 K) by Nakamura, Tanisaki & Obatak6 (1971) and, more recently, as triclinic [P-l; a=7.82 (1) Dove & Rae (1980) who determined the crystal structure. On the other hand, no crystallographic characterization of this transition has yet been Published.…”

“…The F ~ L transition is very slow (so that the F phase * More recently Dove & Rae (1980) have respectively labelled these forms as ~, fl, ~ and ft.…”

Fusion and solid-to-solid transitions of a homologous series of alkane-α,ω-dinitriles

“…those for maloninitrile [1,32,34] and succinonitrile [2]. The investigations of glutaronitrile only provided evidence of the existence of a metastable phase crystal II but the thermodynamic parameters of its transition to crystal I were not determined [4].…”

“…The solid-to-solid transitions of malononitrile have attracted much attention because of the unusual sequence of second-order re-entrant transitions at T = 140 K and T = 295 K. They have been extensively studied by X-ray diffraction [34], Raman scattering [35], nuclear quadrupole resonance [36], and lattice energies calculation for the various phases [33] (table 4). A first-order transition at T = 260 K observed by using calorimetry [32] and nuclear quadrupole resonance [36] was attributed to conversion of the undercooled (metastable) d phase to b phase [35].…”

Protonation of Malononitrile in Superacidic Solutions

“…[2] The CCC angle of protonated malononitrile [113.7(3)°] is slightly ARTICLE widened compared to malononitrile. [7] Both CCN units differ with 175.8(3)°and 177.1(4)°slightly from the expected linear arrangement. The As-F bond lengths of the [AsF 6 ] -anion are in the range between 1.688(2) Å and 1.745(2) Å.…”