Hetero-interpenetrated metal-organic frameworks

Interpenetrated metal-organic frameworks (MOFs) comprise two or more lattices that are mutually entangled. Interpenetration can be used to tune the structures and pore architectures of MOFs to influence, for example, their stability or interactions with guest molecules. The interpenetrating sublattices are typically identical, but hetero-interpenetrated MOFs, which consist of sublattices that are different from one another, have also been serendipitously produced. Here we describe a strategy for the deliberate synthesis of hetero-interpenetrated MOFs. We use the cubic α-MUF-9 framework as a host sublattice to template the growth of a second sublattice within its pores. Three different secondary sublattices are grown-two of which are not known as standalone MOFs-leading to three different hetero-interpenetrated MOFs. This strategy may serve to combine different properties into one material. We produce an asymmetric catalysis by allocating separate roles to the interpenetrating sublattices in a hetero-interpenetrated MOF: an achiral secondary amine on one sublattice provides the catalytic activity, while the chiral α-MUF-10 host imparts asymmetry to aldol and Henry reactions.

Hetero-interpenetrating porous coordination polymers

Interpenetrating porous coordination polymers (IPCPs) consist of two or more networks that are mechanically interlocked to form a coherent structure. The framework topology and the chemical composition are the two important criteria of interpenetrating networks to distinguish homo-IPCPs from hetero-IPCPs. Compared to rich homo-IPCPs, hetero-IPCPs remain rare and are formed rather unexpectedly. This Frontier article highlights hetero-IPCPs in accordance with the difference and/or identity of individual networks in terms of the framework topology and the chemical composition.

Ba-MOFs with tetrazole-based acetic acids: unusual configuration, novel topology and high proton conductivity

Metal-organic frameworks (MOFs) as proton-conductive materials have attracted increasing attention due to their applications in proton-exchange membrane fuel cells. While the majority of the MOFs are based on transition metals, group II metals with unusual configurations have received relatively less attention. In this work, we selected three tetrazole-based acetic acids, N,N-di(2-carboxymethyltetrazol-5-yl)amine (H₂L¹), 1,3,5-tri(2-carboxymethyltetrazol-5-yl)benzene (H₃L²), and 4,5-di(tetrazol-5-yl)imidazolylacetic acid (H₃L³), as ligands and prepared three MOFs with barium(ii) ions: [Ba₂(L¹)₂(H₂O)₅]·2H₂O (1), (Me₂NH₂)[Ba(L²)(H₂O)]·3H₂O (2), and [Ba₃(μ₂-H₂O)(L³)₂(H₂O)₃]·2H₂O (3). Ba-MOFs have been unambiguously characterized by elemental, FT-IR spectroscopy and single-crystal X-ray diffraction analyses. In the solid state, 2D MOF 1 with two nine-coordinated Ba(ii) centers shows a rare hula hoop-like geometry at the Ba1 atom and a distorted tricapped trigonal prismatic geometry around the Ba2 one. Unusual sphenocorona geometry is also found in MOF 2 with a ten-coordinated Ba(ii) ion. In MOF 3, three different Ba(ii) ions coexist with two nine-coordinated Ba1 and Ba2 displaying a muffin-like configuration and a distorted tricapped trigonal prism geometry, respectively, and an eight-coordinated Ba3 having a distorted biaugmented trigonal prism geometry. In addition, MOF 2 exhibits an unprecedented trinodal 3,7,7-connected 3D network with the Schläfli symbol (3⁷·4⁶·5²·6²·7⁴)(3⁷·4⁶·5²·6³·7³)₂(6³) and MOF 3 displays a novel trinodal 4,5,9-connected 3D framework with the Schläfli symbol (4²¹·6¹⁵)(4⁵·6)(4⁸·6²). Due to the presence of extensive hydrogen bonded networks consisting of dimethyl ammonium and water molecules in the 1D channels, MOF 2 shows a high proton conductivity of 4.47 × 10^-3 S cm^-1 at 85 °C and 98% relative humidity (RH).

Tuning the Topology of Three-Dimensional Covalent Organic Frameworks via Steric Control: From to Unprecedented

Whether or not the topology of three-dimensional covalent organic frameworks (3D COFs) can be tuned via steric control remains a big question and has never been reported. Herein, we describe the designed synthesis of two highly crystalline 3D COFs (3D-TPB-COF-OMe and 3D-TPB-COF-Ph), through the polycondensation of tetra(p-aminophenyl)methane and methoxy- or phenyl- substituted 1,2,4,5-tetrakis(4-formylphenyl)benzene on the 3- and 6-positions. Amazingly, by using the continuous rotation electron diffraction technique, 3D-TPB-COF-OMe is determined to have a 5-fold interpenetrated structure with a reported pts net, while 3D-TPB-COF-Ph adopts an unprecedented self-penetrated ljh topology (ljh = Luojia Hill) that does not exist in the database of ToposPro. Therefore, by altering the substituents from methoxy to phenyl groups, the topology of designed 3D COFs changes accordingly, and a rare net is now available. This result clearly demonstrates that such COF structures need to be carefully determined due to its complexity, and moreover, it is promising to design 3D COFs with new topology for interesting application by increasing the steric hindrance of molecular building blocks.

Creative Construction of a Series of Chiral 3D Indium-Organic Frameworks with a umy Topology

Using 2,2'-R₂-biphenyl-4,4'-dicarboxylic acid to bind with a cis-[InO₄(μ₂-OH)₂] octahedron, three novel chiral 3D indium-organic frameworks, [In(μ₂-OH)L] [1, L¹, R = N(CH₃)₂; 2, L², R = OCH₃; 3, L³, R = CH₃], have been hydrothermally synthesized without chiral reagents. Crystal structure analyses reveal that 1-3 show an unprecedented 4-connected umy topology with the Schläfli symbol (4²·6⁴). 1 exhibits high water stability and good sorption selectivity of CO₂ over N₂, while 3 displays high C₂H₂, C₂H₄, and C₂H₆ uptake capacity at 273 K.

Two topologically different 3D CuII metal-organic frameworks assembled from the same ligands: control of reaction conditions

Bifunctional ligands containing both carboxylic and sulfonate groups can adopt versatile coordination modes to produce novel metal-organic frameworks (MOFs) with high-dimensional networks and interesting topologies. Using 2,2'-disulfonylbiphenyl-4,4'-dicarboxylic acid (H₄L) as a linker and 4,4'-bipyridine (4,4'-bpy) as a co-ligand, two novel 3D Cu^II MOFs, {[Cu₂(L)(4,4'-bpy)_2.5(H₂O)]·1.7H₂O}_n, (1), and {[Cu₂(L)(4,4'-bpy)₂]·DMA·3H₂O}_n, (2), have been synthesized and structurally characterized by X-ray crystallography (DMA is N,N-dimethylacetamide). MOF (1) shows an unprecedented trinodal 4,4,5-connected topology network with the Schläfli symbol (4.6².7³)(4³.6⁵.7.8)(6.7³.8.10), while MOF (2) indicates a binodal 4,6-connected fsc network with the Schläfli symbol (4⁴.6¹⁰.8)(4⁴.6²). MOFs (1) and (2) were further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction and thermogravimetric analysis. MOF (1) shows a high water and chemical stability. The proton conductivity of (1) and CO₂ adsorption of (2) were also investigated.

Three novel topologically different metal–organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

The design and synthesis of metal–organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N-dimethylformamide-κO)bis[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ3 O,O′:N]cadmium(II)] N,N-dimethylformamide monosolvate methanol monosolvate], {[Cd(C12H7N2O4)2(C3H7NO)]·C3H7NO·CH3OH} n , (1), poly[[(μ2-acetato-κ2 O:O′)[μ3-3-nitro-4-(pyridin-4-yl)benzoato-κ3 O:O′:N]bis[μ3-3-nitro-4-(pyridin-4-yl)benzoato-κ4 O,O′:O′:N]dicadmium(II)] N,N-dimethylacetamide disolvate monohydrate], {[Cd2(C12H7N2O4)3(CH3CO2)]·2C4H9NO·H2O} n , (2), and catena-poly[[[diaquanickel(II)]-bis[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:N]] N,N-dimethylacetamide disolvate], {[Ni(C12H7N2O4)2(H2O)2]·2C4H9NO} n , (3), have been prepared. Single-crystal structure analysis shows that the CdII atom in MOF (1) has a distorted pentagonal bipyramidal [CdN2O5] coordination geometry. The [CdN2O5] units as 4-connected nodes are interconnected by L − ligands to form a fourfold interpenetrating three-dimensional (3D) framework with a dia topology. In MOF (2), there are two crystallographically different CdII ions showing a distorted pentagonal bipyramidal [CdNO6] and a distorted octahedral [CdN2O4] coordination geometry, respectively. Two CdII ions are connected by three carboxylate groups to form a binuclear [Cd2(COO)3] cluster. Each binuclear cluster as a 6-connected node is further linked by acetate groups and L − ligands to produce a non-interpenetrating 3D framework with a pcu topology. MOF (3) contains two crystallographically distinct NiII ions on special positions. Each NiII ion adopts an elongated octahedral [NiN2O4] geometry. Each NiII ion as a 4-connected node is linked by L − ligands to generate a two-dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW—HW...O hydrogen bonds to form a 3D supramolecular framework. MOFs (1)–(3) were also characterized by powder X-ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid-state photoluminescence of HL and MOFs (1) and (2) have been investigated. The photoluminescence of MOFs (1) and (2) are enhanced and red-shifted with respect to free HL. The gas adsorption investigation of MOF (2) indicates a good separation selectivity (71) of CO2/N2 at 273 K (i.e. the amount of CO2 adsorption is 71 times higher than N2 at the same pressure).

Unprecedented three-dimensional hydrogen-bonded hex topological chiral lanthanide–organic frameworks built from an achiral ligand

The design and preparation of chiral metal–organic frameworks (CMOFs) from achiral ligands are a big challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new linker, a total of eight chiral lanthanide–organic frameworks (LOFs), namely poly[diaquatris[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:O′]lanthanide(III)], L- and D-[Ln(C12H7N2O4)3(H2O)2] n [(1), Ln = Eu; (2), Ln = Gd; (3), Ln = Dy; (4), Ln = Tb], were hydrothermally synthesized without chiral reagents and determined by X-ray crystallography. Crystal structure analyses show that L-(1)–(4) crystallize in the hexagonal P65 space group and are isomorphous and isostructural, while the enantiomers D-(1)–(4) crystallize in the hexagonal P61 space group. All LnIII ions are octacoordinated by six carboxyl O atoms of six 3-nitro-4-(pyridin-4-yl)benzoate ligands and two water molecules in a dodecahedral geometry. A one-dimensional neutral helical [Ln2(CO2)3] n chain is observed in (1)–(4) as a chiral origin. These helical chains are further interconnected via directional hydrogen-bonding interactions between pyridyl groups and water molecules to construct a three-dimensional (3D) homochiral network with hex topology. The present CMOF structure is the first chiral 3D hydrogen-bonded hex-net and shows good water stability. Solid-state circular dichroism (CD) signals revealed that (1)–(4) crystallized through spontaneous resolution. Furthermore, (1) and (4) display a strong red and green photoluminescence at room temperature, respectively, but their intensities reduce to almost half at 200 °C. Notably, upon excitation under visible light (463 nm), a circularly polarized luminescence (CPL) of (1) in the solid state is observed for the first time, with a g lum value of 2.61 × 10−2.

Topological identification of the first uninodal 8-connected lsz MOF built from 2,2′-difluorobiphenyl-4,4′-dicarboxylate pillars and cadmium(II)–triazolate layers

Using polynuclear metal clusters as nodes, many high-symmetry high-connectivity nets, like 8-connnectedbcuand 12-connectedfcu, have been attained in metal–organic frameworks (MOFs). However, construction of low-symmetry high-connected MOFs with a novel topology still remains a big challenge. For example, a uninodal 8-connectedlsznetwork, observed in inorganic ZrSiO4, has not been topologically identified in MOFs. Using 2,2′-difluorobiphenyl-4,4′-dicarboxylic acid (H2L) as a new linker and 1,2,4-triazole (Htrz) as a coligand, a novel three-dimensional CdII–MOF, namely poly[tetrakis(μ4-2,2′-difluorobiphenyl-4,4′-dicarboxylato-κ5O1,O1′:O1′:O4:O4′)tetrakis(N,N-dimethylformamide-κO)tetrakis(μ3-1,2,4-triazolato-κ3N1:N2:N4)hexacadmium(II)], [Cd6(C14H6F2O4)4(C2H2N3)4(C3H7NO)4]n, (I), has been prepared. Single-crystal structure analysis indicates that six different CdIIions co-exist in (I) and each CdIIion displays a distorted [CdO4N2] octahedral geometry with four equatorial O atoms and two axial N atoms. Three CdIIions are connected by four carboxylate groups and four trz−ligands to form a linear trinuclear [Cd3(COO)4(trz)4] cluster, as do the other three CdIIions. Two Cd3clusters are linked by trz−ligands in a μ1,2,4-bridging mode to produce a two-dimensional CdII–triazolate layer with (6,3) topology in theabplane. These two-dimensional layers are further pillared by theL2−ligands along thecaxis to generate a complicated three-dimensional framework. Topologically, regarding the Cd3cluster as an 8-connected node, the whole architecture of (I) is a uninodal 8-connectedlszframework with the Schläfli symbol (422·66). Complex (I) was further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, thermogravimetric analysis and a photoluminescence study. MOF (I) has a high thermal and water stability.

Computational prediction of hetero-interpenetration in metal-organic frameworks

We present a computational algorithm that can screen through a database of metal-organic framework structures and identify materials that lead to hetero-interpenetration with targeted porous materials. Two MOFs (IRMOF-1 and IRMOF-8) were selected as target materials and our algorithm identified PCN-68 and PCN-610 as matching candidates for interpenetration. Molecular simulation results indicate that the interpenetrated MOFs possess enhanced methane and hydrogen adsorption properties compared to the parent materials.

Discovery of hypothetical hetero-interpenetrated MOFs with arbitrarily dissimilar topologies and unit cell shapes

Interpenetration is a commonly observed phenomenon in metal organic frameworks (MOFs) where multiple frameworks are entangled with each other. Using a novel algorithm described here, 18 hypothetical hetero-interpenetrated MOFs were discovered.

Functional group effects on structure and topology of cadmium(ii) frameworks with mixed organic ligands

Cadmium(ii) complexes were obtained by tuning functional groups of benzenedicarboxylate and reaction conditions, their ferroelectric and photoluminescence properties were studied.

Syntheses, structures and luminescence of a series of coordination polymers constructed with 4-substituted 1,2,4-triazole and biscarboxylate co-ligands

Eight coordination polymers were hydrothermal synthesized based on semi-rigid 4-substituted 1,2,4-triazole btpm and biscarboxylate ligands. 1–8 show the structural diversity based on mono-metal, bi-, tri- and tetra-nuclear metal clusters.

CFA-7: an interpenetrated metal–organic framework of the MFU-4 family

Structural characterization of a novel interpenetrated bistriazolate-based MOF followed by postsynthetic replacement of Zn²⁺ by M²⁺ ions (M = Co, Ni, Cu) represents a versatile approach towards redox-active MOFs.

Three sra topological lanthanide–organic frameworks built from 2,2′-dimethoxy-4,4′-biphenyldicarboxylic acid

The first neutral 3D sra-LOF built from a 1D inorganic rod-shaped chain [Ln(CO₂)₂(HCO₂)]_n (Ln = Eu, Gd, Dy) was synthesized.

Synthesis, structure and luminescence properties of a cadmium(ii)-based coordination polymer with (S)-4,4′-bis(4-carboxyphenyl)-2,2′-bis(diphenylphosphinoyl)-1,1′-binaphthyl as chiral linker

[{Cd₂(L)₂(H₂O)}·18 dmf]_n forms a two-dimensional chiral coordination polymer.

A 3D MOF showing unprecedented solvent-induced single-crystal-to-single-crystal transformation and excellent CO2 adsorption selectivity at room temperature

A multifunctional MOF material showing rare solvent-induced structural transformation with substitution of bridging-water and guest-exchange at 298 K is reported.