Using molecular dynamics (MD) simulations, we show that metal-organic frameworks (MOFs) constructed using octahedral Zn4O(CO2)6 clusters linked via aromatic carbon ring structures lead to negative thermal expansion (NTE) behavior (from 0 K to melting). We find that MOF-C22 contracts volumetrically by 1.9% over the range of 0 to 600 K, making it one of the best NTE materials (linear expansion coefficient of a = -11.05 x 10~(-6) K~(-1) compared with a = -9.1 x 10~(-6) K~(-1) found for ZrW2O8, previously the champion NTE material). Indeed, we designed a new MOF using 2-butynediodate linkers that leads to an even larger NTE of 2.2% (from 0 to 500 K). We show that this NTE behavior arises because thermal motions in the rigid Zn-O clusters and the organic moieties linking them lead to tilting of the linkers by successively larger amounts from their alignment along the unit cell axes, resulting in decreased cell parameters. The MOF materials were developed to provide a large reversible hydrogen-storage capacity leading to as much as 73% free volume. However, the NTE properties suggest other possible applications. Thus, their porous but constrained three-dimensional framework provides a framework onto which other materials might blend to form composites with negligible volume change with temperature. To illustrate this, we incorporated polyethylene polymers into MOF-C10 and found that the volume of the composite is constant within 0.059% over the entire range from 300 to 600 K.
展开▼
机译：使用分子动力学（MD）模拟，我们显示使用通过芳香碳环结构连接的八面体Zn4O（CO2）6簇构建的金属有机骨架（MOF）导致负热膨胀（NTE）行为（从0 K到熔化）。我们发现MOF-C22在0至600 K的范围内体积收缩1.9％，使其成为最佳NTE材料之一（线性膨胀系数a = -11.05 x 10〜（-6）K〜（-1）与ZrW2O8（以前是冠军NTE材料）的-9.1 x 10〜（-6）K〜（-1）相比）。实际上，我们设计了一种使用2-丁炔二酸酯连接子的新型MOF，其NTE甚至更高，为2.2％（从0到500 K）。我们表明，这种NTE行为的出现是由于刚性Zn-O团簇中的热运动和连接它们的有机部分导致连接子从其沿晶胞轴的排列连续较大量的倾斜，从而导致细胞参数降低。 MOF材料的开发是为了提供大的可逆储氢能力，从而导致多达73％的自由体积。但是，NTE属性建议其他可能的应用。因此，它们的多孔但受约束的三维框架提供了一个框架，其他材料可以在该框架上混合以形成体积随温度变化可忽略不计的复合材料。为了说明这一点，我们将聚乙烯聚合物掺入了MOF-C10中，发现复合材料的体积在300至600 K的整个范围内恒定在0.059％内。
展开▼
