Näther Christian, Businski Artjom, Herges Rainer
Institut für Anorganische Chemie, Universität Kiel, Germany.
Otto-Diels-Institut für Organische Chemie, Universität Kiel, Germany.
Acta Crystallogr E Crystallogr Commun. 2025 May 9;81(Pt 6):476-481. doi: 10.1107/S2056989025003998. eCollection 2025 Jun 1.
The crystal structure of the title compound, CHNO, was previously reported at 220 K [Businski (2025 ▸). A, 3-8], where it crystallizes in the monoclinic space group 2/ with one crystallographically independent mol-ecule in a general position. In this structure, disorder of the methyl H atoms is observed. However, upon cooling a continuous splitting of the reflections occurs, that might indicate a phase transition. Therefore, data sets were measured between room temperature and 90 K upon cooling and reheating, which shows that a discontinuity in the unit-cell volume occurs between 170 and 180 K. This process is accompanied by the formation of an additional crystal domain. Both domains can be indexed separately, leading to a unit cell similar to that observed at room temperature, but with both α and β angles revealing significant deviations from 90°. Twin refinements clearly show that the structure becomes triclinic (space group 1) upon cooling, resulting in two crystallographically independent mol-ecules in the unit cell, for which some structural changes especially in the conformation and arrangement of the mol-ecules are observed. In the low-temperature structure, disordering of the methyl H atoms is still observed. If the crystal is reheated, the reflections of the second domain disappear and the structure can be successfully refined again in the monoclinic space group 2/, indicating reversibility of the transition.
标题化合物CHNO的晶体结构先前已在220 K下报道[布辛斯基（2025 ▸）。A，3 - 8]，其在单斜空间群2/中结晶，在一般位置有一个晶体学独立分子。在此结构中，观察到甲基氢原子的无序现象。然而，冷却时反射出现连续分裂，这可能表明发生了相变。因此，在冷却和再加热过程中，在室温至90 K之间测量了数据集，结果表明在170至180 K之间晶胞体积出现不连续性。此过程伴随着额外晶体畴的形成。两个畴均可单独指标化，得到一个与室温下观察到的类似的晶胞，但α和β角均明显偏离90°。孪晶精修清楚地表明，冷却时结构变为三斜（空间群1），导致晶胞中有两个晶体学独立分子，观察到它们在分子构象和排列方面有一些结构变化。在低温结构中，仍观察到甲基氢原子的无序现象。如果将晶体再加热，第二个畴的反射消失，结构可在单斜空间群2/中再次成功精修，表明该转变是可逆的。
