Investigation of the synthesis, activation, and isosteric heats of CO₂ adsorption of the isostructural series of metal-organic frameworks M₃(BTC)₂ (M = Cr, Fe, Ni, Cu, Mo, Ru)

The synthesis, activation, and heats of CO₂ adsorption for the known members of the M₃(BTC)₂ (HKUST-1) isostructural series (M = Cr, Fe, Ni, Zn, Ni, Cu, Mo) were investigated to gain insight into the impact of CO₂–metal interactions for CO₂ storage/separation applications. With the use of modified syntheses and activation procedures, improved BET surface areas were obtained for M = Ni, Mo, and Ru. The zero-coverage isosteric heats of CO₂ adsorption were measured for the Cu, Cr, Ni, Mo, and Ru analogues and gave values consistent with those reported for MOFs containing coordinatively unsaturated metal sites, but lower than for amine functionalized materials. Notably, the Ni and Ru congeners exhibited the highest CO₂ affinities in the studied series. These behaviors were attributed to the presence of residual guest molecules in the case of Ni₃(BTC)₂(Me₂NH)₂(H₂O) and the increased charge of the dimetal secondary building unit in [Ru₃(BTC)₂][BTC].Massachusetts Institute of Technology. Energy Initiative (Seed Fund

Complexes of Platinum Group Metals with a Conformationally Locked Scorpionate in a Metal–Organic Framework: An Unusually Close Apical Interaction of Palladium(II)

We report synthetic strategies for installing platinum group metals (PGMs: Pd, Rh, Ir, and Pt) on a scorpionate-derived linker (TpmC*) within a metal-organic framework (MOF), both by room-temperature postsynthetic metalation and by direct solvothermal synthesis, with a wide range of metal loadings relevant for fundamental studies and catalysis. In-depth studies for the palladium adduct Pd(II)@Zr-TpmC* by density-functional-theory-assisted extended X-ray absorption fine structure spectroscopy reveals that the rigid MOF lattice enforces a close Pd(II)-Napical interaction between the bidentate palladium complex and the third uncoordinated pyrazole arm of the TpmC* ligand (Pd-Napical = 2.501 ± 0.067 Å), an interaction that is wholly avoided in molecular palladium scorpionates

Divergent Adsorption Behavior Controlled by Primary Coordination Sphere Anions in the Metal–Organic Framework Ni 2 X 2 BTDD

CO, ethylene, and H2 demonstrate divergent adsorption enthalpies upon interaction with a series of anion-exchanged Ni2X2BTDD materials (X = OH, F, Cl, Br; H2BTDD = bis(1H-1,2,3-triazolo[4,5-b][4',5'-i])dibenzo[1,4]dioxin)). The dissimilar responses of these conventional π-acceptor gaseous ligands are in contrast with the typical behavior that may be expected for gas sorption in metal-organic frameworks (MOFs), which generally follows similar periodic trends for a given set of systematic changes to the host MOF structure. A combination of computational and spectroscopic data reveals that the divergent behavior, especially between CO and ethylene, stems from a predominantly σ-donor interaction between the former and Ni2+ and a π-acceptor interaction for the latter. These findings will facilitate further deliberate postsynthetic modifications of MOFs with open metal sites to control the equilibrium selectivity of gas sorption

Thousand-fold increase in O₂ electroreduction rates with conductive MOFs

Molecular materials must deliver high current densities to be competitive with traditional heterogeneous catalysts. Despite their high density of active sites, it has been unclear why the reported O2 reduction reaction (ORR) activity of molecularly defined conductive metal–organic frameworks (MOFs) have been very low: ca. −1 mA cm–2. Here, we use a combination of gas diffusion electrolyses and nanoelectrochemical measurements to lift multiscale O2 transport limitations and show that the intrinsic electrocatalytic ORR activity of a model 2D conductive MOF, Ni3(HITP)2, has been underestimated by at least 3 orders of magnitude. When it is supported on a gas diffusion electrode (GDE), Ni3(HITP)2 can deliver ORR activities >−150 mA cm–2 and gravimetric H2O2 electrosynthesis rates exceeding or on par with those of prior heterogeneous electrocatalysts. Enforcing the fastest accessible mass transport rates using scanning electrochemical cell microscopy revealed that Ni3(HITP)2 is capable of ORR current densities exceeding −1200 mA cm–2 and at least another 130-fold higher ORR mass activity than has been observed in GDEs. Our results directly implicate precise control over multiscale mass transport to achieve high-current-density electrocatalysis in molecular materials

Simultaneous interlayer and intralayer space control in two-dimensional metal−organic frameworks for acetylene/ethylene separation

© 2020, The Author(s). Three-dimensional metal−organic frameworks (MOFs) are cutting-edge materials in the adsorptive removal of trace gases due to the availability of abundant pores with specific chemistry. However, the development of ideal adsorbents combining high adsorption capacity with high selectivity and stability remains challenging. Here we demonstrate a strategy to design adsorbents that utilizes the tunability of interlayer and intralayer space of two-dimensional fluorinated MOFs for capturing acetylene from ethylene. Validated by X-ray diffraction and modeling, a systematic variation of linker atom oxidation state enables fine regulation of layer stacking pattern and linker conformation, which affords a strong interlayer trapping of molecules along with cooperative intralayer binding. The resultant robust materials (ZUL-100 and ZUL-200) exhibit benchmark capacity in the pressure range of 0.001–0.05 bar with high selectivity. Their efficiency in acetylene/ethylene separation is confirmed by breakthrough experiments, giving excellent ethylene productivities (121 mmol/g from 1/99 mixture, 99.9999%), even when cycled under moist conditions