Single crystals are typically brittle, inelastic materials. Such mechanical responses limit their use in practical applications, particularly in flexible electronics and optical devices. Here we describe single crystals of a well-known coordination compound—copper(II) acetylacetonate—that are flexible enough to be reversibly tied into a knot. Mechanical measurements indicate that the crystals exhibit an elasticity similar to that of soft materials such as nylon, and thus display properties normally associated with both hard and soft matter. Using microfocused synchrotron radiation, we mapped the changes in crystal structure that occur on bending, and determined the mechanism that allows this flexibility with atomic precision. We show that, under strain, the molecules in the crystal reversibly rotate, and thus reorganize to allow the mechanical compression and expansion required for elasticity and still maintain the integrity of the crystal structure.

中文翻译：

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乙酰丙酮铜（II）弹性晶体结构变化的原子分辨率

单晶通常是脆性的，无弹性的材料。这种机械响应限制了它们在实际应用中的使用，尤其是在柔性电子和光学设备中。在这里，我们描述了一种著名的配位化合物铜（II）的单晶乙酰丙酮酸酯-具有足够的柔韧性，可逆地打成一个结。机械测量表明，该晶体显示出与诸如尼龙之类的软材料相似的弹性，因此显示出通常与硬物质和软物质均相关的性质。使用微聚焦同步加速器辐射，我们绘制了弯曲时晶体结构的变化，并确定了以原子精度实现这种灵活性的机制。我们表明，在应变下，晶体中的分子可逆旋转，并因此重组以允许弹性所需的机械压缩和膨胀，并且仍然保持晶体结构的完整性。