Defect-controlled MOF Mechanics

In our previous work we discovered that UiO-66, one of the canonical metal-organic frameworks (MOFs), can contain correlated defects, and showed that we have a degree of synthetic control over the presence and distribution of defects.

In this paper we use this control over defects to tune the physical properties of UiO-66. In particular, we look at the thermomechanical properties of UiO-66 - its response to changing temperature - examine how they change with different concentrations of defects. We also show that the behaviour of UiO-66 on heating is pretty unusual. First, it rapidly densifies when heated to about 300 ^oC (as loosely bound molecules are driven off). Second, this densified material exhibits ‘colossal’ isotropic negative thermal expansion - i.e. when heated it shrinks in every direction.

We measured these thermomechanical properties by carrying out variable temperature powder X-ray diffraction measurements at the Diamond Light Source, which allowed us to very precisely measure the size of the unit cell.

A short summary was published on the Chemistry World blog.