The linker orientation in conformational isomers of DUT-8(Ni) determines the flexibility of this metal–organic framework.

The development of adsorbents with molecular precision offers a promising strategy to enhance storage of hydrogen and methaneconsidered the fuel of the future and a transitional fuel, respectivelyand to realize a carbon-neutral energy cycle. Herein we employ a postsynthetic modification strategy on a robust metal–organic framework (MOF), MFU-4l, to boost its storage capacity toward these clean energy gases. MFU-4l-Li displays one of the best volumetric deliverable hydrogen capacities of 50.2 g L–1 under combined temperature and pressure swing conditions (77 K/100 bar → 160 K/5 bar) while maintaining a moderately high gravimetric capacity of 9.4 wt %. Moreover, MFU-4l-Li demonstrates impressive methane storage performance with a 5–100 bar usable capacity of 251 cm3 (STP) cm–3 (0.38 g g–1) and 220 cm3 (STP) cm–3 (0.30 g g–1) at 270 and 296 K, respectively. Notably, these hydrogen and methane storage capacities are significantly improved compared to those of its isoreticular analogue, MFU-4l, and place MFU-4l-Li among the best MOF-based materials for this application.

Flexible metal-organic Frameworks (MOFs) are an interesting class of materials due to their diverse properties. One representative of this class is the layered-pillar MOF DUT-8(Ni). This MOF consists of Ni 2 paddle wheels interconnected by naphthalene dicarboxylate linkers and dabco pillars (Ni 2 (ndc) 2 (dabco), ndc = 2,6-naphthalene-dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane). DUT-8(Ni) undergoes a volume change of over 140% upon adsorption of guest molecules. Herein, a ligand field molecular mechanics (LFMM) study of the CO 2 -induced flexibility of DUT-8(Ni) is presented. LFMM is able to reproduce experimental and DFT structural features as well as properties that require large simulation cells. It is shown that the transformation energy from a closed to open state of the MOF is overcompensated fivefold by the host-guest interactions. Structural characteristics of the MOF explain the shape of the energy profile at different loading states and provide useful insights to the interpretation of previous experimental results.the possibilities of employing ligand field molecular mechanics (LFMM) simulations to study flexible MOFs and their processes. The method employed is not limited to adsorption processes but as has been shown previously [8][9][10][11] to be applicable to other properties, for example, spin states or magnetic properties. Our goal is to present simulations using the example of CO 2induced breathing in the pillared layer MOF DUT-8(Ni) [12] (Ni 2 (ndc) 2 (dabco), ndc = 2,6naphthalenedicarboxylate, dabco = 1,4diazabicyclo-[2.2.2]-octane, see Figure 1) using an LFMM approach. Motivated by its outstanding properties, DUT-8(Ni) is being investigated extensively recently. [12][13][14][15][16][17][18][19][20][21][22][23] Some examples of the properties of interest are the enormous volume change upon opening (more than 140 %), [14] its isomorphism, [22] the property dependence on the metal center, [14] and crystallite size effects. [19] Alzahrani and Deeth [24] already employed LFMM to investigate clusters of Zn 2 (bdc) 2 (dabco) and showed the applicability to this structurally related flexible MOF. We present here the first application of LFMM to simulate the breathing of an openshell transition-metal paddle wheel pillared layer MOF in periodic boundary conditions.

In this work, we investigate the adsorption of chlorinated methanes (CH x Cl4–x , x = 0–4) in a representative layer-pillar metal–organic framework, the flexible MOF Ni2(ndc)2(dabco) (ndc = 2,6-naphthalene-dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane), also known as DUT-8­(Ni). The guest molecules show a systematic increase of polarizability with increasing number of chlorine atoms, whereas the dipole moment exceeds 2 debye for x = 2 and 3. Our ligand field molecular mechanics simulations show that, at first, counter-intuitively, the host–guest interactions are mainly characterized by London dispersion despite the molecular dipole moments reaching magnitudes as large as water. This highlights the importance of London dispersion interactions in the description of host–guest interactions.