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

Helically Chiral Hybrid Cyclodextrin Metal-Organic Framework Exhibiting Circularly Polarized Luminescence

Three achiral polycyclic aromatic fluorophores─namely, 1-pyrenecarboxylic acid, 9-anthracenecarboxylic acid, and perylene-3,9-dicarboxylic acid─were chosen based on their desired properties before being incorporated into the construction of a K⁺-carrying gamma-cyclodextrin (γ-CD)-based metal-organic framework (CD-MOF-1) and γ-CD-containing hybrid frameworks (CD-HFs). Among these fluorophores, only the pyrene-carrying one shows significant noncovalent bonding interactions with γ-CD in solution. This fluorophore is encapsulated in a CD-HF with a trigonal superstructure instead of the common cubic CD-MOF-1 found in the case of the other two fluorophores. Single-crystal X-ray diffraction analysis of the trigonal CD-HF reveals a π-stacked chiral positioning of the pyrene-carrying fluorophore inside the (γ-CD)₂ tunnels and held uniformly around an enantiomorphous 3₂ screw axis along the c direction in the solid-state structure. This helix-like structure demonstrates an additional level of chirality over and above the point-chiral stereogenic centers of γ-CD and the axial chirality associated with the self-assembled π-stacked fluorophores. These arrangements result in specifically generated photophysical and chiroptical properties, such as the controlled emergence of circularly polarized luminescence (CPL) emission. In this manner, a complete understanding of the mechanism of chirality transfer from a chiral host (CD-HF) to an encapsulated achiral fluorophore has been achieved, an attribute which is often missing in the development of materials with CPL.

A new 3D 8-connected Cd(ii) MOF as a potent photocatalyst for oxytetracycline antibiotic degradation

1 exhibits the best photocatalytic decomposition efficiency towards antibiotic OXY. The plausible photocatalytic mechanism has been explained with the help of the density of states calculations and Hirshfeld surface analysis.

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.

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

A whole series of [Ln(H2O)4(Ala)2]26+ dimeric cationic lanthanide complexes with both L- and D-alanine enantiomers was synthesized. The single-crystal X-ray diffraction at 100 and 292 K shows the formation of two types of dimers (I and II) in crystals. Between the dimer centers, the alanine molecules behave as bridging (μ2-O,O'-) and chelating bridging (μ2-O,O,O'-) ligands. The first type of bridge is present in dimers I, while both bridge forms can be observed in dimers II. The IR and vibrational circular dichroism (VCD) spectra of all L- and D-alanine complexes were registered in the 1750-1250 cm-1 range as KBr pellets. Despite all the studied complexes are exhibiting similar crystal structures, the spectra reveal correlations or trends with the Ln-O1 distances which exemplify the lanthanide contraction effect in the IR spectra. This is especially true for the positions and intensities of some IR bands. Unexpectedly, the ν(C=O) VCD bands are quite intense and their composed shapes reveal the inequivalence of the C=O vibrators in the unit cell which vary with the lanthanide. Unlike in the IR spectra, the ν(C=O) VCD band positions are only weakly correlated with the change of Ln and the VCD intensities at most show some trends. Nevertheless, this is the first observation of the lanthanide contraction effect in the VCD spectra. Generally, for the heavier lanthanides (Ln: Dy-Lu), the VCD band maxima are very close to each other and the mirror reflection of the band of two enantiomers is usually better than that of the lighter Lns. DFT calculations show that the higher the multiplicity the higher the stability of the system. Actually, the molecular geometry in crystals (at 100 K) is well predicted based on the highest-spin structures. Also, the simulated IR and VCD spectra strongly depend on the Ln electron configuration but the best overall agreement was reached for the Lu complex, which is the only system with a fully filled f-shell.

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).