Selective CO₂ capture in metal-organic frameworks with azine-functionalized pores generated by mechanosynthesis

Two new three-dimensional porous Zn(II)-based metal-organic frameworks, containing azine-functionalized pores, have been readily and quickly isolated via mechanosynthesis, by using a nonlinear dicarboxylate and linear N-donor ligands. The use of nonfunctionalized and methyl-functionalized N-donor ligands has led to the formation of frameworks with different topologies and metal-ligand connectivities and therefore different pore sizes and accessible volumes. Despite this, both metal-organic frameworks (MOFs) possess comparable BET surface areas and CO₂ uptakes at 273 and 298 K at 1 bar. The network with narrow and interconnected pores in three dimensions shows greater affinity for CO compared to the network with one-dimensional and relatively large pores-attributable to the more effective interactions with the azine groups

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

Structural, Thermodynamic, and Transport Properties of the Small-Gap Two-Dimensional Metal-Organic Kagomé Materials Cu₃(hexaiminobenzene)₂ and Ni₃(hexaiminobenzene)₂

Metal-organic frameworks (MOFs) provide exceptional chemical tunability and have recently been demonstrated to exhibit electrical conductivity and related functional electronic properties. The kagomé lattice is a fruitful source of novel physical states of matter, including the quantum spin liquid (in insulators) and Dirac fermions (in metals). Small-bandgap kagomé materials have the potential to bridge quantum spin liquid states and exhibit phenomena such as superconductivity but remain exceptionally rare. Here we report a structural, thermodynamic, and transport study of the two-dimensional kagomé metal-organic frameworks Ni3(HIB)2 and Cu3(HIB)2 (HIB = hexaiminobenzene). Magnetization measurements yield Curie constants of 0.989 emu K (mol Ni)-1 Oe-1 and 0.371 emu K (mol Cu)-1 Oe-1, respectively, close to the values expected for ideal S = 1 Ni2+ and S = 1/2 Cu2+. Weiss temperatures of -10.6 and -14.3 K indicate net weak mean field antiferromagnetic interactions between ions. Electrical transport measurements reveal that both materials are semiconducting, with gaps (Eg) of 22.2 and 103 meV, respectively. Specific heat measurements reveal a large T-linear contribution γof 148(4) mJ mol-fu-1 K-2 in Ni3(HIB)2 with only a gradual upturn below 5 K and no evidence of a phase transition to an ordered state down to 0.1 K. Cu3(HIB)2 also lacks evidence of a phase transition above 0.1 K, with a substantial, field-dependent, magnetic contribution below 5 K. Despite them being superficially in agreement with the expectations of magnetic frustration and spin liquid physics, we ascribe these observations to the stacking faults found from a detailed analysis of synchrotron X-ray diffraction data. At the same time, our results demonstrate that these MOFs exhibit localized magnetism with simultaneous proximity to a metallic state, thus opening up opportunities to explore the connection between the insulating and metallic ground states of kagomé materials in a highly tunable chemical platform. © 2022 American Chemical Society

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

Mechanistic Evidence for Ligand-Centered Electrocatalytic Oxygen Reduction with the Conductive MOF Ni3(hexaiminotriphenylene)2

Establishing catalytic structure-function relationships introduces the ability to optimize the catalyst structure for enhanced activity, selectivity, and durability against reaction conditions and prolonged catalysis. Here we present experimental and computational data elucidating the mechanism for the O2 reduction reaction with a conductive nickel-based metal-organic framework (MOF). Elucidation of the O2 reduction electrokinetics, understanding the role of the extended MOF structure in providing catalytic activity, observation of how the redox activity and pKa of the organic ligand influences catalysis, and identification of the catalyst active site yield a detailed O2 reduction mechanism where the ligand, rather than the metal, plays a central role. More generally, familiarization with how the structural and electronic properties of the MOF influence reactivity may provide deeper insight into the mechanisms by which less structurally defined nonplatinum group metal electrocatalysts reduce O2

Mechanistic Evidence for Ligand-Centered Electrocatalytic Oxygen Reduction with the Conductive MOF Ni3(hexaiminotriphenylene)2

Establishing catalytic structure-function relationships introduces the ability to optimize the catalyst structure for enhanced activity, selectivity, and durability against reaction conditions and prolonged catalysis. Here we present experimental and computational data elucidating the mechanism for the O2 reduction reaction with a conductive nickel-based metal-organic framework (MOF). Elucidation of the O2 reduction electrokinetics, understanding the role of the extended MOF structure in providing catalytic activity, observation of how the redox activity and pKa of the organic ligand influences catalysis, and identification of the catalyst active site yield a detailed O2 reduction mechanism where the ligand, rather than the metal, plays a central role. More generally, familiarization with how the structural and electronic properties of the MOF influence reactivity may provide deeper insight into the mechanisms by which less structurally defined nonplatinum group metal electrocatalysts reduce O2