Frustrated flexibility in metal-organic frameworks

Abstract

Stimuli-responsive flexible metal-organic frameworks (MOFs) remain at the forefront of porous materials research due to their enormous potential for various technological applications. Here, we introduce the concept of frustrated flexibility in MOFs, which arises from an incompatibility of intra-framework dispersion forces with the geometrical constraints of the inorganic building units. Controlled by appropriate linker functionalization with dispersion energy donating alkoxy groups, this approach results in a series of MOFs exhibiting a new type of guest- and temperature-responsive structural flexibility characterized by reversible loss and recovery of crystalline order under full retention of framework connectivity and topology. The stimuli-dependent phase change of the frustrated MOFs involves non-correlated deformations of their inorganic building unit, as probed by a combination of global and local structure techniques together with computer simulations. Frustrated flexibility may be a common phenomenon in MOF structures, which are commonly regarded as rigid, and thus may be of crucial importance for the performance of these materials in various applications.

Mechanically interlocked molecules in metal–organic frameworks

“…The phase transition induced by a stimulus has also been applied to topologically rigid MOFs prepared with non-interlocked linkers. Such reticular systems show a breathing phenomenon of the pores, 120 converting, for example, insulator materials into conductor ones 121 or generating frustrated flexible hybrid MOFs, 122 among others. The development of the design of MIM-containing MOFs with reversible phase changes could be focused on these intriguing behaviours for obtaining flexible and functional dynamic MOFs.…”

Multivariate analysis of disorder in metal–organic frameworks

“…Disorder is emerging as an increasingly prevalent and powerful means to drive functionality within framework materials 1 . Once regarded as ‘perfect’ crystalline structures, they have been found to harbour a variety of types of disorder 2 – 5 . Even frameworks ostensibly believed to be highly symmetric and rigid, such as UiO-66, have been found to possess some degree of disorder 6 , 7 .…”

Quantification of gas-accessible microporosity in metal-organic framework glasses

“…10,11 In recent years defective, disordered and amorphous MOFs have gained more and more attention since these materials provide access to new and unusual properties beyond the state of the art. [12][13][14][15][16][17][18][19][20] Especially solidto-liquid transitions of MOFs are exciting, as they offer processing and shaping of the framework materials in their liquid state (i.e. above their melting temperature, Tm) and vitrification to a MOF glass after cooling below their glass transition temperature (Tg).…”