Two binary transition metal cyanamides, Zr(CN₂)₂ and Hf(CN₂)₂, were prepared by solid-state metathesis (SSM) reactions and separately controlled by differential thermoanalysis (DTA). The crystal structure of Hf(CN₂)₂ was solved and refined from a single-phase crystal powder by X-ray diffraction (XRD) in the space group Pbcn. Zr(CN₂)₂ was characterized by isotypic indexing. The crystal structure of M(CN₂)₂ compounds with M = Zr, Hf is closely related to that of LiY(CN₂)₂, but reveals large cavities due to the absence of lithium ions. Hf(CN₂)₂ exhibits thermoelastic properties characteristic of a flexible framework material. The calculated phonon energies, elastic tensor, and thermal expansion tensor are presented; the volumetric coefficient of thermal expansion is predicted to be near-zero under ambient conditions (α_V = −3.5 × 10⁻⁶ K⁻¹).

中文翻译：

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Zr（CN ₂）₂和Hf（CN ₂）₂ †的合成及热弹性

通过固态复分解（SSM）反应制备了两种二元过渡金属氰胺Zr（CN ₂）₂和Hf（CN ₂）₂，并分别通过差热分析（​​DTA）进行控制。通过在空间群Pbcn中的X射线衍射（XRD）从单相晶体粉末中解析和精制了Hf（CN ₂）₂的晶体结构。Zr（CN ₂）_2的特征是通过同型索引。M = Zr，Hf的M（CN ₂）₂化合物的晶体结构与LiY（CN ₂）₂的晶体结构密切相关，但由于缺少锂离子而显示出大的空洞。Hf（CN ₂）₂表现出柔性框架材料的热弹性特性。给出了计算出的声子能量，弹性张量和热膨胀张量。热膨胀的体积系数被预测为在环境条件下几乎为零（α _V = -3.5×10 ^-6 ķ ^-1）。