Metal−Organic Frameworks Provide Large Negative Thermal Expansion Behavior

Abstract

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 α = −11.05 × 10-6 K-1 compared with α = −9.1 × 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 a...