†Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland.
‡Department of Chemistry and Polymer Science, University of Stellenbosch, Stellenbosch 7600, South Africa.
J Am Chem Soc. 2015 Jul 29;137(29):9296-301. doi: 10.1021/jacs.5b03280. Epub 2015 May 26.
A soft porous material [Zn(L)2(OH)2]n·Guest (where L is 4-(1H-naphtho[2,3-d]imidazol-1-yl)benzoate, and Guest is water or methanol) exhibits the strongest ever observed negative area compressibility (NAC), an extremely rare property, as at hydrostatic pressure most materials shrink in all directions and few expand in one direction. This is the first NAC reported in metal-organic frameworks (MOFs), and its magnitude, clearly visible and by far the highest of all known materials, can be reversibly tuned by exchanging guests adsorbed from hydrostatic fluids. This counterintuitive strong NAC of [Zn(L)2(OH)2]n·Guest arises from the interplay of flexible [-Zn-O(H)-]n helices with layers of [-Zn-L-]4 quadrangular puckered rings comprising large channel voids. The compression of helices and flattening of puckered rings combine to give a giant piezo-mechanical response, applicable in ultrasensitive sensors and actuators. The extrinsic NAC response to different hydrostatic fluids is due to varied host-guest interactions affecting the mechanical strain within the range permitted by exceptionally high flexibility of the framework.
一种软质多孔材料 [Zn(L)2(OH)2]n·Guest（其中 L 是 4-(1H-萘并[2,3-d]咪唑-1-基)苯甲酸酯，而 Guest 是水或甲醇）表现出迄今为止观察到的最强负面积压缩性（NAC），这是一种极为罕见的性质，因为在静水压力下，大多数材料在各个方向上都会收缩，很少有材料在一个方向上膨胀。这是在金属-有机骨架（MOFs）中首次报道的 NAC，其幅度之大，在所有已知材料中显然是最高的，并且可以通过从静压流体中吸附的客体的交换来可逆地调节。这种与直觉相反的 [Zn(L)2(OH)2]n·Guest 强 NAC 来自于柔性 [-Zn-O(H)-]n 螺旋与包含大通道空隙的 [-Zn-L-]4 四方形褶皱环层之间的相互作用。螺旋的压缩和平坦化的褶皱环共同产生了巨大的压电器械响应，可应用于超灵敏传感器和执行器。对不同静压流体的外在 NAC 响应是由于不同的主体-客体相互作用影响了在框架极高柔性允许的范围内的机械应变。
