Ambient-pressure trigonal phase α of selenourea SeC(NH₂)₂ is noncentrosymmetric, with high Z′ = 9. Under high pressure it undergoes several intriguing transformations, depending on the pressure-transmitting medium and the compression or recrystallization process. In glycerine or oil, α-SeC(NH₂)₂ transforms into phase β at 0.21 GPa; however in water, phase α initially increases its volume and can be compressed to 0.30 GPa due to the formation of α-SeC(NH₂)₂·xH₂O. The single crystals of α-SeC(NH₂)₂ and of its partial hydrate α-SeC(NH₂)₂·xH₂O are shattered by pressure-induced transitions. Single crystals of phase β-SeC(NH₂)₂ were in situ grown in a diamond-anvil cell and studied by X-ray diffraction. The monoclinic phase β is centrosymmetric, with Z′ = 2. It is stable to 3.20 GPa at least, but it cannot be recovered at ambient conditions due to strongly strained NH…Se hydrogen bonds. No hydrogen-bonding motifs present in the urea structures have been found in selenourea phases α and β.

中文翻译：

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硒脲中的高压和环境效应及其分子周围的不稳定晶体场

硒脲 SeC(NH ₂ ) _{2 的}环境压力三角相 α 是非中心对称的，具有高Z ' = 9。在高压下，它经历了几个有趣的转变，这取决于压力传输介质和压缩或再结晶过程。在甘油或油中，α-SeC(NH ₂ ) ₂在 0.21 GPa 时转化为相 β；然而，在水中，α相最初会增加其体积，并且由于形成 α-SeC(NH ₂ ) ₂ · x H ₂ O ，可以压缩到 0.30 GPa。α -SeC(NH ₂ ) ₂和其部分水合物 α-SeC(NH ₂) ₂ · x H ₂ O 被压力引起的转变击碎。相位β-SEC（NH单晶₂）₂分别为在原位生长在金刚石砧细胞，并通过X射线衍射分析。单斜相 β 是中心对称的，Z ′ = 2。它至少在 3.20 GPa 下是稳定的，但由于强应变的 NH…Se 氢键，它无法在环境条件下恢复。在硒脲相 α 和 β 中没有发现尿素结构中存在的氢键基序。