X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
J Am Chem Soc. 2013 May 22;135(20):7621-8. doi: 10.1021/ja4012707. Epub 2013 May 14.
Systematic exploration of the molecular framework material Zn(CN)2 at high pressure has revealed several distinct series of transitions leading to five new phases: four crystalline and one amorphous. The structures of the new crystalline phases have been resolved through ab initio structural determination, combining charge flipping and direct space methods, based on synchrotron powder diffraction data. The specific transition activated under pressure depends principally on the pressure-transmitting fluid used. Without fluid or in large molecule fluids (e.g., isopropanol, ethanol, or fluorinert), the high-pressure behavior intrinsic to Zn(CN)2 is observed; the doubly interpenetrated diamondoid framework structure transforms to a distorted, orthorhombic polymorph, Zn(CN)2-II (Pbca) at ~1.50-1.58 GPa with asymmetric displacement of the bridging CN ligand and reorientation of the Zn(C/N)4 tetrahedra. In small molecule fluids (e.g., water, methanol, methanol-ethanol-water), the nonporous interpenetrated Zn(CN)2 framework can undergo reconstructive transitions to porous, non-interpenetrated polymorphs with different topologies: diamondoid (dia-Zn(CN)2, Fd3m, P(trans) ~ 1.2 GPa), londaleite (lon-Zn(CN)2, P6(3)/mmc, P(trans) ~ 0.9 GPa), and pyrite-like (pyr-Zn(CN)2, Pa3, P(trans) ~ 1.8 GPa). Remarkably, these pressure-induced transitions are associated with near 2-fold volume expansions. While an increase in volume with pressure is counterintuitive, the resulting new phases contain large fluid-filled pores, such that the combined solid + fluid volume is reduced and the inefficiencies in space filling by the interpenetrated parent phase are eliminated. That both dia-Zn(CN)2 and lon-Zn(CN)2 phases were retained upon release to ambient pressure demonstrates the potential for application of hydrostatic pressures to interpenetrated framework systems as a novel means to generate new porous materials.
在高压下对分子框架材料 Zn(CN)2 进行系统探索，揭示了导致五个新相的几个不同系列的转变：四个晶相和一个非晶相。通过基于同步辐射粉末衍射数据的电荷翻转和直接空间方法的组合，对新晶相的结构进行了从头算结构确定。在压力下激活的特定转变主要取决于所使用的加压流体。没有流体或在大分子流体（例如异丙醇、乙醇或氟利昂）中，观察到 Zn(CN)2 的固有高压行为；双穿插的金刚石骨架结构转变为扭曲的正交多晶型物 Zn(CN)2-II（Pbca），在1.50-1.58 GPa 下，桥接 CN 配体的不对称位移和 Zn(C/N)4 四面体的重定向。在小分子流体（例如水、甲醇、甲醇-乙醇-水）中，无孔穿插的 Zn(CN)2 骨架可以经历重建性转变，形成具有不同拓扑结构的多孔非穿插多晶型物：金刚石型（dia-Zn(CN)2，Fd3m，P(trans)1.2 GPa）、隆代尔石型（lon-Zn(CN)2，P6(3)/mmc，P(trans)0.9 GPa）和黄铁矿型（pyr-Zn(CN)2，Pa3，P(trans)1.8 GPa）。值得注意的是，这些压力诱导的转变伴随着近 2 倍的体积膨胀。虽然随着压力的增加体积增加是违反直觉的，但新相包含大的充满流体的孔，使得固-液总体积减少，并且穿插母相的空间填充效率降低。在释放到环境压力时保留了 dia-Zn(CN)2 和 lon-Zn(CN)2 相，这表明将静水压力应用于穿插骨架系统作为生成新多孔材料的一种新方法具有潜力。
