3,6-Connected Metal–Organic Frameworks Based on Triscarboxylate as a 3-Connected Organic Node and a Linear Trinuclear Co₃(COO)₆ Secondary Building Unit as a 6-Connected Node

The solvothermal reactions of cobalt­(II) chloride hexahydrate and 1,3,5-benzenetribenzoic acid (H₃BTB) in anhydrous <i>N</i>,<i>N</i>′-dimethylacetamide (DMA) at two different reaction temperatures and reactant concentrations led to two 3,6-connected metal–organic frameworks (MOFs) with different net topologies based on the ligand as a <i>C</i>₃ symmetric 3-connected organic node and the linear trinuclear cobalt carboxylate cluster, Co₃(COO)₆, as a 6-connected secondary building unit (SBU). MOF [Co₃(BTB)₂(DMA)₄], <b>1</b>, with a linear trinuclear cobalt carboxylate cluster, Co₃(COO)₆, and with an inversion point symmetry with “compressed trigonal antiprismatic” 6-connectivity, is a two-dimensional (2-D) layered structure of a 3,6-connected <b>kgd</b> net topology. However, the same linear trinuclear cobalt carboxylate cluster, Co₃(COO)₆, with a 2-fold point symmetry with “compressed trigonal prismatic” 6-connectivity leads to the three-dimensional (3-D) network of <b>2</b>, with an unprecedented 3,6-connected net topology with the point symbol (4³)₂(4³·12¹²). The 2-D layered framework, <b>1</b>, shows a significant sorption hysteresis for adsorbates with relatively strong interactions with the framework, such as N₂ and CO₂

3,6-Connected Metal–Organic Frameworks Based on Triscarboxylate as a 3-Connected Organic Node and a Linear Trinuclear Co₃(COO)₆ Secondary Building Unit as a 6-Connected Node

The solvothermal reactions of cobalt­(II) chloride hexahydrate and 1,3,5-benzenetribenzoic acid (H₃BTB) in anhydrous <i>N</i>,<i>N</i>′-dimethylacetamide (DMA) at two different reaction temperatures and reactant concentrations led to two 3,6-connected metal–organic frameworks (MOFs) with different net topologies based on the ligand as a <i>C</i>₃ symmetric 3-connected organic node and the linear trinuclear cobalt carboxylate cluster, Co₃(COO)₆, as a 6-connected secondary building unit (SBU). MOF [Co₃(BTB)₂(DMA)₄], <b>1</b>, with a linear trinuclear cobalt carboxylate cluster, Co₃(COO)₆, and with an inversion point symmetry with “compressed trigonal antiprismatic” 6-connectivity, is a two-dimensional (2-D) layered structure of a 3,6-connected <b>kgd</b> net topology. However, the same linear trinuclear cobalt carboxylate cluster, Co₃(COO)₆, with a 2-fold point symmetry with “compressed trigonal prismatic” 6-connectivity leads to the three-dimensional (3-D) network of <b>2</b>, with an unprecedented 3,6-connected net topology with the point symbol (4³)₂(4³·12¹²). The 2-D layered framework, <b>1</b>, shows a significant sorption hysteresis for adsorbates with relatively strong interactions with the framework, such as N₂ and CO₂

Crystal-to-Crystal Transformations of a Series of Isostructural Metal–Organic Frameworks with Different Sizes of Ligated Solvent Molecules

Isostructural 3D metal–organic frameworks (MOFs) [Zn₂(BTC)­(NO₃)­S₃] [where BTC = 1,3,5-benzenetricarboxylate; S = EtOH (<b>1</b>), DMF (<b>2</b>), DMA (<b>3</b>), or DEF (<b>4</b>)] of a 3-connected <b>srs</b> net topology have been prepared in the presence of serine as a template. The MOFs show different framework stabilities depending on the sizes of the ligated solvent molecules and undergo a crystal-to-crystal transformation at ambient conditions into a 1D chain structure either directly or via different types of intermediates depending on the ligated solvent molecules and the sample handling conditions. A single crystal of the MOF with the ligated DMF molecules, [Zn₂(BTC)­(NO₃)­(DMF)₃] (<b>2</b>), is stable in Mg^II- and Co^II-DMF solutions; however, it transforms into a single particle-like microcrystalline aggregate of Cu-HKUST-1 in a Cu^II-DMF solution

Postsynthetic Exchanges of the Pillaring Ligand in Three-Dimensional Metal–Organic Frameworks

Metal–organic frameworks, [Ni­(HBTC)­(dabco)] (<b>2</b>) and [Ni₂(HBTC)₂(bipy)_0.6(dabco)_1.4] (<b>3</b>) (where H₃BTC is 1,3,5-benzenetricarboxylic acid, dabco is 1,4-diazabicyclo[2.2.2]­octane, and bipy is 4,4′-bipyridine), were prepared via postsynthetic ligand exchanges of [Ni­(HBTC)­(bipy)] (<b>1</b>). By controlling the concentration of dabco, we could obtain not only entropically favorable <b>2</b> with completely exchanged dabco but also enthalpically favorable <b>3</b> with selectively exchanged bipy/dabco in the alternating layers

Combinational Synthetic Approaches for Isoreticular and Polymorphic Metal–Organic Frameworks with Tuned Pore Geometries and Surface Properties

Isoreticular and polymorphic 3-D MOFs were prepared via the combination of direct solvothermal reactions, postsynthetic ligand exchanges of the MOFs prepared via the direct solvothermal reactions, and postsynthetic ligand insertions into a 2-D MOF. The appropriate pore dimensions, surface areas, and adsorption enthalpies of the MOFs combined well to produce the largest working CO₂ capture capacities via the pressure swing adsorption process

Combinational Synthetic Approaches for Isoreticular and Polymorphic Metal–Organic Frameworks with Tuned Pore Geometries and Surface Properties

Isoreticular and polymorphic 3-D MOFs were prepared via the combination of direct solvothermal reactions, postsynthetic ligand exchanges of the MOFs prepared via the direct solvothermal reactions, and postsynthetic ligand insertions into a 2-D MOF. The appropriate pore dimensions, surface areas, and adsorption enthalpies of the MOFs combined well to produce the largest working CO₂ capture capacities via the pressure swing adsorption process

Solvent-Induced Structural Dynamics in Noninterpenetrating Porous Coordination Polymeric Networks

Three novel soft porous coordination polymer (PCP) or metal–organic framework (MOF) compounds have been synthesized with a new rigid ligand <i>N</i>-(4-pyridyl)-1,4,5,8-naphathalenetetracarboxymonoimide (PNMI) by partial hydrolysis of <i>N,N′</i>-di-(4-pyridyl)-1,4,5,8-naphthalenete-tracarboxydiimide (DPNI) during solvothermal reactions with Zn­(II), Cd­(II), and Mn­(II) salts, and they are [Zn­(PNMI)]·2DMA (<b>1</b>·2DMA, <b>1a</b>), [Cd­(PNMI)]·0.5DMA·5H₂O (<b>2</b>·0.5DMA·5H₂O), and [Mn­(PNMI)]·0.75DMF (<b>3</b>·0.75DMF). The structure of <b>1</b> is based on paddle-wheel secondary building unit (SBU) with a 3,6-connected <b>rtl</b> net topology, whereas <b>2</b> and <b>3</b> are isotypical but the M­(O₂C–C)₂ fragments aggregate in one-dimension and the overall connectivity is the same <b>rtl</b> net topology. All these three MOFs have one-dimensional rhombic channels filled with guest molecules. The guest molecules in <b>1a</b> can be exchanged with EtOH in a single-crystal to single-crystal (SCSC) manner to <b>1</b>·1.25EtOH·0.375H₂O (<b>1b</b>). Further, the guest molecules in <b>1b</b> can be replaced with ethylene glycol, triethylene glycol and allyl alcohol without destroying its single crystal nature. These guest exchanges are accompanied by reduction in volume of the unit cell up to 16%, as well as the void volume up to 33.1%. Similarly, triethylene glycol (TEGly) selectively exchanges EtOH in a mixture of the above solvents, which might be the result of correct fit of the hydrogen-bonded TEGly dimer in the channel of <b>1</b>. While activated <b>1</b> and <b>3</b> exhibit no uptake of N₂ and H₂ at 1 bar and 77 K and very low uptake of CO₂ gas at 1 bar and 196 K, activated <b>2</b> shows selective CO₂ uptake, 278 cm²·g^–1, over N₂ and H₂ at 1 bar and 196 K, which corresponds to 5.87 molecules of CO₂ per formula unit of <b>2</b>

Post-Synthetic Modifications of Framework Metal Ions in Isostructural Metal–Organic Frameworks: Core–Shell Heterostructures via Selective Transmetalations

The transmetalation (the replacement of metal ions) of a family of highly porous isostructural metal–organic frameworks (MOFs), M₆(BTB)₄(BP)₃ (where M = Zn­(II) (<b>1</b>), Co­(II) (<b>2</b>), Cu­(II) (<b>3</b>), and Ni­(II) (<b>4</b>), BTB = 1,3,5-benzenetribenzoate, and BP = 4,4′-dipyridyl) with an <b>ith-d</b> net topology has been investigated. These compounds have different framework stabilities depending on the framework metal ions. The transmetalation and the reverse transmetalation reactions of the framework metal ions were observed between the MOFs, <b>1</b> and <b>2</b>, having a similar thermodynamic stability. While the transmetalation from thermodynamically less stable <b>1</b> and <b>2</b> to more stable <b>3</b> and <b>4</b> were achieved by soaking single crystals of <b>1</b> and <b>2</b> in a solution of <i>N,N</i>′-dimethylformamide (DMF) containing Cu­(II) and Ni­(II) ions, respectively, no reverse transmetalation was observed. By simply controlling the soaking time, not only could homogeneously transmetalated crystalline framework structures be prepared via the thermodynamically controlled complete replacement of the framework metal ions but also selectively transmetalated core–shell heterostructures were formed via kinetically controlled replacement that was mainly restricted to the external shell region of the crystal. The fully transmetalated MOFs showed significantly improved framework stabilities compared with the parent MOFs. A marked improvement in the framework stability was observed, even in the selectively transmetalated Co­(II)/Cu­(II)- and Co­(II)/Ni­(II)-core–shell heterostructures. Although the frameworks are partially transmetalated, the framework stability of not only the external shell region but also of the internal core region was significantly affected

Symmetry-Mismatched SBU Transformation in MOFs: Postsynthetic Metal Exchange from Zn to Fe and Its Effects on Gas Adsorption and Dye Selectivity

This research explores the alteration of metal–organic frameworks (MOFs) using a method called postsynthetic metal exchange. We focus on the shift from a Zn-based MOF containing a [Zn4O(COO)6] secondary building unit (SBU) of octahedral site symmetry (ANT-1(Zn)) to a Fe-based one with a [Fe3IIIO(COO)6]+ SBU of trigonal prismatic site symmetry (ANT-1(Fe)). The symmetry-mismatched SBU transformation cleverly maintains the MOF’s overall structure by adjusting the conformation of the flexible 1,3,5-benzenetribenzoate linker to alleviate the framework strain. The process triggers a decrease in the framework volume and pore size alongside a change in the framework’s charge. These alterations influence the MOF’s ability to adsorb gas and dye. During the transformation, core–shell MOFs (ANT-1(Zn@Fe)) are formed as intermediate products, demonstrating unique gas sorption traits and adjusted dye adsorption preferences due to the structural modifications at the core–shell interface. Heteronuclear clusters, located at the framework interfaces, enhance the heat of CO2 adsorption. Furthermore, they also influence the selectivity of the dye size. This research provides valuable insights into fabricating novel MOFs with unique properties by modifying the SBU of a MOF with flexible organic linkers from one site symmetry to another