Three highly crystalline and porous COFs with promising photoredox properties have been prepared. Via a post-sulfurization process, the imine-linked COFs were converted into thiazole-linked COFs, generating a highly conjugated and ultrastable photocatalyst for H ₂ O ₂ production.

Synthesis of 2D MOFs is often sensitive to the reaction conditions like temperature and solvent etc. Cu(II)-5-azidoisophthalate MOF (Cu(II)–5N₃IP) has been synthesized at room temperature as well as under solvothermal conditions. The azide functional group remained stable during solvothermal synthesis at 85 °C. Cu(II)–5N₃IP crystallized in a Kagomé-type structure. Typical Cu₂ paddle-wheels are connected to each other by 5N₃IP ligands in infinite 2D sheets in the (001) plane, featuring 1D infinite channels within each layer. This MOF is used for the adsorption of methylene blue (MB), rhodamine B (RhB), methyl orange (MO), and Congo red (CR). The adsorption is selective to the dimensions, shapes and ionic strengths of the dyes. Cu(II)–5N₃IP exhibited adsorption rates in the order MB > CR > RhB > MO. Cu(II)–5N₃IP is used as a catalyst for aerobic oxidation and Knoevenagel condensation. 3–10 mol% of Cu–5N₃IP selectively catalyzes the oxidation of benzyl alcohol to benzaldehyde in 9–20 h at 60 °C. In Knoevenagel condensation, the reaction of both unsubstituted and substituted benzaldehydes at room temperature was observed at a very low catalyst loading of 3 mol% of MOF within a short time of 3–60 min. This 2D MOF has proved to be more efficient for dye adsorption and the catalytic applications under investigation (such as alcohol oxidation and Knoevenagel condensation) than its analogous 3D or 0D materials.

The hydrothermal reactions of 1,2,4,5-cyclohexanetetracarboxylic acid (H₄L) with CoCl₂·2H₂O and rigid or semi-rigid bis(imidazole) ligands were able to generate two Co(II) coordination polymers (CPs), {[Co₅(L)₂(1,4-bimb)(μ₃-OH)₂(H₂O)₈]·2H₂O}_n (1), {[Co(L)_0.5(1,4-bib)]·H₂O}_n (2) (1,4-bimb = 1,4-bis(imidazol-1-ylmethyl)benzene, 1,4-bib = 1,4-bis(1H-imidazol-1-yl)benzene). CPs 1 and 2 were structurally characterized by elemental analysis, IR spectroscopy, X-ray powder diffraction and single crystal X-ray diffraction. CP 1 features a 3D 3,3,4,4,5-connected framework with an unprecedented {4²·8·10²·12}{4³·6·8⁶}₂{4³}₂{4⁶}₂{6²·8}₂ topology, which represents the first example of CPs with such a topology. CP 2 possesses a three-fold interpenetration 3D framework with mog topology. The distinct structures of the two CPs may result from diverse coordination modes of the (L)⁴⁻ ligands and different structural characteristics of rigid or semi-rigid N-donor ligands. The thermal stabilities, photoluminescence properties and electrochemical behavior in the solid state for CPs 1 and 2 have been investigated. The photophysical studies indicated that CPs 1 and 2 are potential semiconductive materials. Moreover, both CPs 1 and 2 show high photocatalytic efficiency for the degradation of methylene blue (MB) under UV light irradiation and exhibit good stability and recyclability. A possible photocatalytic mechanism is speculated by introducing t-butyl alcohol (TBA) as a widely used ˙OH scavenger.

In this review, the challenges of COF synthesis are tackled. Discussion of mechanistic studies and improved synthetic methods pave the way for high quality materials and an increased understanding of the underlying chemistry.

Six Co(II)-based coordination polymers (CPs) with characteristic frameworks and topologies—namely, [Co(L1)(DCTP)]_n (1), [Co(L2)(DCTP)]_n (2), [Co(L3)(DCTP)]_n (3), {[Co₃(L4)₃(DCTP)₃·H₂O]·H₂O}_n (4), [Co(L5)_1.5(DCTP)]_n (5) and [Co(L6)(DCTP)]_n (6)—were successfully hydrothermally synthesized by employing the halogenated linear ligand 2,5-dichloroterephthalic acid (H₂DCTP). The interpenetrated structures could be rationally modulated by auxiliary N-donor co-ligands containing 1,1′-(1,4-butanediyl)bis-1H-benzimidazole (L1), 1,4-bis(5,6-dimethylbenzimidazol-1-yl)-2-butylene (L2), 1,2-bis(2-methylbenzimidazol-1-ylmethyl)benzene (L3), 1,4-bis(2-methylbenzimidazol-1-ylmethyl)benzene (L4), 1,2-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (L5) and 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (L6). These diaphanous crystals were clearly characterized by elemental analysis, infrared (IR) spectra and X-ray powder diffraction (XRPD) as well as single-crystal X-ray diffraction analysis. With the aid of the flexible N-donor co-ligands, CP 1 occupies a non-interpenetrated 2D sheet with the point symbol {4⁴·6²} sql net topology, CP 2 possesses a 3D hexagon-shaped network with the point symbol {6⁶} three-fold interpenetrated sqc6 topology, CP 3 exhibits a 2D layer with the point symbol {4⁴·6²} sql net topology, CP 4 reveals an unusual 3D framework with the point symbol {4²·6³·8} three-fold interpenetrated sra topology, CP 5 has a 3D hexagon-shaped network with the point symbol {6⁶} two-fold interpenetrated sqc6 topology, while CP 6 displays a 3D hexagon-shaped network with the point symbol {6⁶} three-fold interpenetrated sqc6 topology. The diverse structures of CPs 1–6 illustrate that the substitute group and position of the methyl group of the bis(benzimidazole) derivatives play a significant role in the assembly of such interpenetrated frameworks. Moreover, luminescence properties and thermal behavior, as well as the electrochemical and photocatalytic properties of CPs 1–6 on the degradation of methylene blue, are also presented.