Non-Crystallinity and Disorder in Dynamic Metal-Organic Frameworks – Responsiveness, Melting and Glass-Formation
Sebastian Henke a
a Technische Universität Dortmund, 44221 Dortmund, Georgia
Proceedings of Dynamic Materials, Crystals and Phenomena Conference (DynaMIC23)
Fribourg, Switzerland, 2023 March 22nd - 24th
Organizers: Jovana Milic and Simon Krause
Invited Speaker, Sebastian Henke, presentation 013
Publication date: 15th February 2023

Metal-organic frameworks (MOFs) are an emerging family of porous solid-state materials exhibiting huge potential for various technological applications (gas storage/separation, catalysis, drug delivery, sensing, etc.). Even though research has primarily focused on the crystalline state of these materials, non-crystalline or amorphous MOFs have received increasing attention recently. This is because of the emergence of novel properties associated to the non-crystalline state, such us meltability and glass formation or unusual structural responsiveness. This talk will cover our recent investigations in the area of non-crystalline and highly disordered MOFs.

Firstly, the phenomenon of frustrated flexibility in MOFs based on the renowned [Zn4O(O2C)6] building unit is introduced. An incompatibility of intra-framework dispersion forces with the geometrical constraints of the [Zn4O(O2C)6] building units results in a new type of guest-responsive structural flexibility of the frustrated MOFs, characterized by reversible loss and recovery of crystalline order under full retention of framework connectivity and topology.[1] A combination of global and local structure techniques reveals stimuli-dependent aperiodic deformations of the inorganic building units as the origin of the unique structural behavior of these MOFs. Some of those materials additionally display a unique thermal behaviour, where increasing the temperature increases the crystalline order of the aperiodically distorted frameworks. This unprecedented entropy-driven disorder-order transition will be discussed in detail.

Secondly, our recent work on liquid and glassy MOFs of the family of zeolitic imidazolate frameworks (ZIFs) is presented. We outline chemical design rules for the systematic modulation of the ZIFs thermal and mechanical properties,[2,3] including tuning the melting point and the corresponding glass transition temperature of the derived glasses. First insights into the intrinsic porosity of the ZIF glasses and how the porosity depends on the choice of the molecular building blocks are introduced.[3,4] Our results set the stage for the application of such MOF glasses as novel functional amorphous materials in kinetic gas separation, solid-state ionic conduction and optics.

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