Construction of 2D Interdigitated Polyrotaxane Layers and their Transformation to a 3D Polyrotaxane by a Photocycloaddition Reaction between Wheels

Following the pioneering work of Sauvage and Stoddart on rotaxanes, construction of higher dimensional polyrotaxanes in metal-organic frameworks (MOFs) via a modified protocol is challenging. We present the formation of a two-dimensional (2D) polyrotaxane and its conversion to a three-dimensional (3D) polyrotaxane MOF via a photoreaction between interdigitated "olefin wheels". For this purpose, a 2-fold entangled 2D MOF [Pb₂(bpp)(sdc)₂] (1), showing a 2D + 2D → 2D polyrotaxane motif, has been synthesized from the solvothermal reaction of lead(II) nitrate, 3,3'-stilbenedicarboxylic acid (H₂sdc) containing an olefin group, and 1,4-bis(4-pyridyl)piperazine (bpp). The single-crystal X-ray diffraction analysis of 1 revealed that the adjacent entangled 2D layers are interdigitated, with the separation of 3.72 Å between C═C bond pairs in adjacent layers satisfying Schmidt's criteria for the occurrence of a [2 + 2] photocycloaddition reaction. Irradiation of the single crystals of 1 under UV light resulted in formation of a 3D polyrotaxane, [Pb₂(bpp)(rctt-tccb)]_n (2), due to a [2 + 2] photocycloaddition reaction between two wheels via a single-crystal to single-crystal transformation. The photocycloaddition and partial thermal cleavage reaction between 1 and 2 were confirmed by ¹H NMR and powder X-ray diffraction (PXRD) in solution and the solid state, respectively. The present approach could contribute to the understanding of the construction of higher dimensional polyrotaxanes which are not accessible by the traditional routes.

Two-fold interpenetrated Mn-based metal–organic frameworks (MOFs) as battery-type electrode materials for charge storage

Two novel interpenetrated 2-fold Mn-MOFs were successfully prepared and applied for the first time in a charge-storage field. As a result, the bulk electrodes behave as alkaline batteries and deliver high capacities of 1004 and 619 C g⁻¹ at 1 A g⁻¹.

A new CdII coordination polymer with a self-penetrating architecture induced by the molecular conformation of a rigid bithiophene ligand

The design and synthesis of coordination polymers with a self-penetrating architecture has attracted much interest not only due to their interesting structures but also due to their potential applications. 5,5'-Bis(pyridin-4-yl)-2,2'-bithiophene (bpbp), as a conjugated bithiophene ligand, can exhibit trans and cis conformations and this can lead to the construction of a self-penetrating architecture. In addition, the semi-rigid ancillary ligand 4,4'-oxybis(benzoic acid) (H₂oba) can adopt different coordination modes, resulting in coordination polymers with high-dimensional skeletons. A new Cd^II coordination polymer based on mixed ligands, namely poly[diaquapentakis[μ-5,5'-bis(pyridin-4-yl)-2,2'-bithiophene-κ²N:N']bis(nitrato-κ²O,O')tetrakis(μ₃-4,4'-oxydibenzoato)-κ¹⁰O:O,O':O'',O''';κ⁶O:O':O''-pentacadmium(II)], [Cd₅(C₁₄H₁₄O₅)₄(NO₃)₂(C₁₈H₁₂N₂S₂)₅(H₂O)₂]_n, (I), has been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction indicates that there are three crystallographically independent Cd^II cations, three bpbp ligands, two deprotonated oba^2- ligands, one nitrate ligand and one coordinated water molecule in the asymmetric unit. One Cd^II centre is seven-coordinated, exhibiting a distorted {CdN₂O₅} pentagonal bipyramidal geometry, while the other two Cd centres are both six-coordinated, showing slightly distorted {CdN₂O₄} octahedral geometries. The most interesting feature is the co-existence of trans and cis conformations in a single net, allowing structural interpenetration via self-threading and yet the expected self-penetrating structure was obtained. Topological analysis shows that the whole three-dimensional framework can be classified as a 3-nodal (4,6,6)-c net with Schläfli symbol {6¹³.8²}₂{6⁶}, which is a new topology. Furthermore, the luminescence properties of (I) were examined in the solid state at room temperature.

Seven entangled coordination polymers assembled from triphenylamine-based bisimidazole and dicarboxylates: interpenetration, self-penetration and mixed entanglement

Seven entangled coordination polymers constructed from a triphenylamine-based bisimidazole and carboxylic acids have been synthesized and characterized.

Syntheses, structures and properties of five entangled coordination polymers constructed with trigonal N-donor ligands

Five new entangled coordination polymers, which are based on large trigonal N-donor ligands and polycarboxylates, are reported. They display different entangled nets with self-penetrating, polythreading, interdigitation and interpenetration features.

DMF/H2O Volume-Ratio-Controlled Assembly of 2D and 3D Ln-MOFs with 5-(Pyridin-4-yl)isophthalic Acid Ligand

Through middle-temperature solvothermal reactions of Ln(NO3)3·6H2O (Ln = Tb and Eu) with 5-(pyridin-4-yl)isophthalic acid (H2PIA), three Ln-MOFs [Tb(HPIA)(PIA)(H2O)2]n·0.5nH2O (1), [Eu(HPIA)(PIA)(H2O)2]n·0.5nH2O (2), and [Tb2(PIA)3(H2O)4]n·3nH2O (3) were obtained using DMF/H2O volume ratios of 1 : 54, 1 : 54, and 1 : 7, respectively. Single-crystal X-ray diffraction analysis reveals that complexes 1 and 2 are isostructural and display a 2D uninodal 4-connected undulated sql topology with Ln3+ ions as nodes, while complex 3 exhibits a 3D uninodal 6-connected pcu topology with dinuclear octahedral [Tb2(CO2)6] secondary building units as nodes. Obviously, the DMF/H2O volume ratio plays an essential role in the crystallisation and construction of these coordination frameworks with distinct dimensionality and connectivity. The thermal and photoluminescence properties of complexes 1–3 in the solid state are also discussed.