Dynamic in situ X-ray diffraction reveals unexpected intermediate crystal structures
Dynamic in situ X-ray diffraction reveals unexpected intermediate crystal structures lead image
The ability to uptake and release guest molecules through their pores like sponges makes metal-organic frameworks (MOFs) useful for applications including pollution sequestration, fuel storage, and more. Walton et al. developed a new technique called a dynamic in situ single-crystal X-ray diffraction to track transformation of the MOF crystal [Co(AIP)(bpy)0.5(H2O)]•2H2O during its dehydration.
While the MOF lost its three H2O molecules, the authors studied its intermediate structures using a specially-equipped X-ray diffractometer. They were surprised to see that instead of losing one water molecule at a time, the MOF lost one H2O very rapidly and then the next two simultaneously.
They found that the MOF undergoes unexpected structural transformations during dehydration, underlining the importance of using methods like dynamic in situ single-crystal X-ray diffraction to see unintuitive, short-lived, metastable, intermediate structures, even though they are more difficult to study than beginning and end structures.
“To make these materials by design to uptake special molecules, we have to be able to understand how the materials function throughout the entirety of their phase transitions, not just the beginning and end structures,” said author Jason Benedict.
This technique could be used to study guest molecule exchange in other nanoporous materials, as well as dynamic processes happening in crystals beyond guest exchange.
Next, the authors will attempt to use the same technique on crystals smaller than hundreds of micrometers, and on faster time scales. This will allow them to study the first rapid water molecule loss with greater time resolution.
Source: “Determination of the dehydration pathway in a flexible metal-organic framework by dynamic in situ X-ray diffraction,” by Ian M. Walton, Jordan M. Cox, Shea D. Myers, Cassidy A. Benson, Travis B. Mitchell, Gage S. Bateman, Eric D. Sylvester, Yu-Sheng Chenb, and Jason B. Benedict, Structural Dynamics (2020). The article can be accessed at https://doi.org/10.1063/4.0000015 .
