Due to an error in the implementation of the analysis routine that extracts the average total potential energy ⟨U⟩ from the trajectory data, the reported values for ΔU are too small by a constant factor of 7 in the case of the periodic simulations in this manuscript. Due to this constant factor, Figures 5b and 6b are essentially identical, with, however, a scaled ordinate. The corrected figures are shown in Figure 1 and 2. As a consequence, the derived entropy contributions −TΔS to the free energy ΔA for the periodic reference case were also incorrect in the published article. The corrected Figure 6c of the original manuscript is now given in Figure 3. Due to the negligible temperature dependence of ΔU, the entropy contribution is still the dominating factor that destabilizes the cp phase at higher temperature as concluded in the original manuscript. The erroneous values for ΔU cp−op , ΔU ‡ cp−op , ΔS cp−op reported in Table S1 in the supporting information have been corrected in Table 1 and volumes for the cp and op phases were added. The Column ΔS ‡ was removed due to the absence of an entropic barrier in the corrected data.

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.

Flexible metal-organic frameworks (MOFs) show large structural flexibility as a function of temperature or (gas)pressure variation, a fascinating property of high technological and scientific relevance. The targeted design of flexible MOFs demands control over the macroscopic thermodynamics as determined by microscopic chemical interactions and remains an open challenge. Herein we apply high-pressure powder X-ray diffraction and molecular dynamics simulations to gain insight into the microscopic chemical factors that determine the high-pressure macroscopic thermodynamics of two flexible pillared-layer MOFs. For the first time we identify configurational entropy that originates from side-chain modifications of the linker as the key factor determining the thermodynamics in a flexible MOF. The study shows that configurational entropy is an important yet largely overlooked parameter, providing an intriguing perspective of how to chemically access the underlying free energy landscape in MOFs.

The post-synthetic installation of linker molecules between open-metal sites (OMSs) and undercoordinated metal-nodes in a metal-organic framework (MOF) — retrofitting — has recently been discovered as a powerful tool to manipulate macroscopic properties such as the mechanical robustness and the thermal expansion behavior. So far, the choice of cross linkers (CLs) that are used in retrofitting experiments is based on qualitative considerations. Here, we present a low-cost computational framework that provides experimentalists with a tool for evaluating various CLs for retrofitting a given MOF system with OMSs. After applying our approach to the prototypical system CL@Cu3BTC2 (BTC = 1,3,5-benzentricarboxylate) the methodology was expanded to NOTT-100 and NOTT-101 MOFs, identifying several promising CLs for future CL@NOTT-100 and CL@NOTT-101 retrofitting experiments. The developed model is easily adaptable to other MOFs with OMSs and is set-up to be used by experimentalists, providing a guideline for the synthesis of new retrofitted MOFs with modified physicochemical properties.

For the structure prediction of MOFs and related crystalline framework materials we have proposed the Reversed Topological Approach (RTA), where the default embedding of a topology is used as a blueprint. The optimal rotational insertion of the building blocks (BBs) at the fixed vertex positions of the blueprint is performed by minimizing the target function of the average angle deviation (AAD). Here we extend this idea by pre-optimizing the maximum symmetry embedding of a topology in order to minimize the overall mean AAD for the given set of BBs. By this fast and essentially parameter-free topoFF method, the vertex positions and cell parameters of the blueprint are further optimized in order to fit the structural needs of the BBs, which speeds up the overall search for the most energetically favorable structure. In addition, different topologies can be ranked in a quantitative and intuitive way. The definition and implementation of topoFF is explained and its application for the RTA-based structure prediction of MOFs is demonstrated with a number of instructive examples.