Cooperative Cluster Metalation and Ligand Migration in Zirconium Metal–Organic Frameworks

Zr- and Ti-based metal-organic frameworks: synthesis, structures and catalytic applications

Recently, Zr- and Ti-based metal-organic frameworks (MOFs) have gathered increasing interest in the field of chemistry and materials science, not only for their ordered porous structure, large surface area, and high thermal and chemical stability, but also for their various potential applications. Particularly, the unique features of Zr- and Ti-based MOFs enable them to be a highly versatile platform for catalysis. Although much effort has been devoted to developing Zr- and Ti-based MOF materials, they still suffer from difficulties in targeted synthesis, especially for Ti-based MOFs. In this Feature Article, we discuss the evolution of Zr- and Ti-based MOFs, giving a brief overview of their synthesis and structures. Furthermore, the catalytic uses of Zr- and Ti-based MOF materials in the previous 3-5 years have been highlighted. Finally, perspectives on the Zr- and Ti-based MOF materials are also proposed. This work provides in-depth insight into the advances in Zr- and Ti-based MOFs and boosts their catalytic applications.

Optimizing Fe-Based Metal-Organic Frameworks through Ligand Conformation Regulation for Efficient Dye Adsorption and C2 H2 /CO2 Separation

Regulating the structure of metal-organic frameworks (MOFs) by adjusting the ligands reasonably is expected to enhance the interaction of MOFs on special molecules/ions, which has significant application value for the selective adsorption of guest molecules. Herein, two tricarboxylic ligands H₃ L-Cl and H₃ L-NH₂ were designed and synthesized based on the ligand H₃ TTCA by replacing part of the benzene rings with C=C bonds and modifying the chlorine and amino groups on the 4-position of the benzene ring. Two 3D Fe-MOFs (UPC-60-Cl and UPC-60-NH₂ ) with the new topology types were constructed. As the C=C bonds of the ligands have flexible torsion angles, UPC-60-Cl features three types of irregular 2D channels, while UPC-60-NH₂ has a cage with two types of windows on the surface. The synergistic effect of unique channels and modification of functional groups endows UPC-60-Cl and UPC-60-NH₂ with high adsorption capacity for organic dyes. Compound UPC-60-Cl shows high adsorption capacity for CV (147.2 mg g^-1 ), RHB (100.3 mg g^-1 ), and MO (220.9 mg g^-1 ), whereas UPC-60-NH₂ exhibits selective adsorption of MO (158.7 mg g^-1 ). Meanwhile, based on the diverse pore structure and modification of active sites, UPC-60-Cl and UPC-60-NH₂ show the selective separation of equimolar C₂ H₂ /CO₂ . Therefore, reasonable regulation of organic ligands plays a significant role in guiding the structure diversification and performance improvement of MOFs.

Sequential Transformation of Zirconium(IV)-MOFs into Heterobimetallic MOFs Bearing Magnetic Anisotropic Cobalt(II) Centers

Heterometallic metal-organic frameworks (MOFs) allow the precise placement of various metals at atomic precision within a porous framework. This new level of control by MOFs promises fascinating advances in basic science and application. However, the rational design and synthesis of heterometallic MOFs remains a challenge due to the complexity of the heterometallic systems. Herein, we show that bimetallic MOFs with MX₂ (INA)₄ moieties (INA=isonicotinate; M=Co²⁺ or Fe²⁺ ; X=OH^- , Cl^- , Br^- , I^- , NCS^- , or NCSe^- ) can be generated by the sequential modification of a Zr-based MOF. This multi-step modification not only replaced the linear organic linker with a square planar MX₂ (INA)₄ unit, but also altered the symmetry, unit cell, and topology of the parent structure. Single-crystal to single-crystal transformation is realized so that snapshots for transition process were captured by successive single-crystal X-ray diffraction. Furthermore, the installation of Co(NCS)₂ (INA)₄ endows field-induced slow magnetic relaxation property to the diamagnetic Zr-MOF.

Stabilizing and Organizing Bi3 Cu4 and Bi7 Cu12 Nanoclusters in Two-Dimensional Metal-Organic Networks

Multinuclear heterometallic nanoclusters with controllable stoichiometry and structure are anticipated to possess promising catalytic, magnetic, and optical properties. Heterometallic nanoclusters with precise stoichiometry of Bi₃ Cu₄ and Bi₇ Cu₁₂ can be stabilized in the scaffold of two-dimensional metal-organic networks on a Cu(111) surface through on-surface metallosupramolecular self-assembly processes. The atomic structures of the nanoclusters were resolved using scanning tunneling microscopy and density functional theory calculations. The nanoclusters feature highly symmetric planar hexagonal shapes and core-shell charge modulation. The clusters are arranged as triangular lattices with a periodicity that can be tuned by choosing molecules of different size. This work shows that on-surface metallosupramolecular self-assembly creates unique possibilities for the design and synthesis of multinuclear heterometallic nanoclusters.

Ethylene oligomerization in metal–organic frameworks bearing nickel(ii) 2,2′-bipyridine complexes

The metal–organic frameworks Zr₆O₄(OH)₄(bpydc)₆ (1; bpydc²⁻ = 2,2′-bipyridine-5,5′-dicarboxylate) and Zr₆O₄(OH)₄(bpydc)_0.84(bpdc)_5.16 (2; bpdc²⁻ = biphenyl-4,4′-dicarboxylate) were readily metalated with Ni(DME)Br₂ (DME = dimethoxyethane) to produce the corresponding metalated frameworks 1(NiBr₂)₆ and 2(NiBr₂)_0.84. Both nickel(ii)-containing frameworks catalyze the oligomerization of ethylene in the presence of Et₂AlCl. In these systems, the pore environment around the active nickel sites significantly influences their selectivity for formation of oligomers over polymer. Specifically, the single-crystal structure of 1(NiBr₂)_5.64 reveals that surrounding metal–linker complexes enforce a steric environment on each nickel site that causes polymer formation to become favorable. Minimizing this steric congestion by isolating the nickel(ii) bipyridine complexes in the mixed-linker framework 2(NiBr₂)_0.84 markedly improves both the catalytic activity and selectivity for oligomers. Furthermore, both frameworks give product mixtures that are enriched in shorter olefins (C_4–10), leading to deviations from the expected Schulz–Flory distribution of oligomers. Although these deviations indicate possible pore confinement effects on selectivity, control experiments using the nickel-treated biphenyl framework Zr₆O₄(OH)₄(bpdc)₆(NiBr₂)_0.14 (3(NiBr₂)_0.14) reveal that they likely arise at least in part from the presence of nickel species that are not ligated by bipyridine within 1(NiBr₂)_5.64 and 2(NiBr₂)_0.84.