Defect-controlled MOF Mechanics

UiO-66(Hf) 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.

Paper

Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework

M J Cliffe, J A Hill, C A Murray, F-X Coudert, A L Goodwin

Phys Chem Chem Phys, 17, 11586-11592 (2015).

This article is also available on the arXiv.
Open access link.
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