Two isostructural Zn/Co-MOFs with penetrating structures: multifunctional properties of both luminescence sensing and conversion of CO2 into cyclic carbonates.

Two new metal-organic frameworks (MOFs), namely, {[Zn(HL)(bpea)]·DMF}n (Zn-MOF-1) and {[Co(HL)(bpea)]·DMF}n (Co-MOF-2) (H3L = 3-(3,5-dicarboxybenzyloxy)benzoic acid, bpea = 1,2-di(pyridyl)ethane), were obtained by the reaction of H3L and N-containing ligand bpea with Zn(NO3)2·6H2O and Co(NO3)2·6H2O, respectively. The isomorphic Zn-MOF-1 and Co-MOF-2 featured a 3D penetrating framework with different stabilities, luminescence, and catalytic properties. Luminescence measurement indicated that Zn-MOF-1 could be used to detect Al3+ through a turn-on effect with a detection limit of 0.42 µM. The sensing mechanism experiments showed that the enhanced luminescence of Zn-MOF-1 toward Al3+ may be due to the weak interaction between Al3+ and Zn-MOF-1 and the absorbance-caused enhancement (ACE) mechanism. Meanwhile, both Zn-MOF-1 and Co-MOF-2 showed interesting CO2 adsorption properties and could catalyze the cycloaddition of CO2 to epoxides resulting in 96 and 92% ideal products within 12 hours, respectively. They can be cycled up to 5 times without significant loss of catalytic efficiency.

A novel (3,6)-connected CdII coordination polymer based on an ether-linked tricarboxylate ligand: synthesis, topology and luminescence sensing properties in aqueous solution.

A novel three-dimensional coordination polymer, namely, poly[[diaquabis(µ-4,4'-bipyridine)bis{µ3-5-[(2-carboxyphenoxy)methyl]isophthalato}tricadmium(III)] dimethylformamide monosolvate 2.5-hydrate], {[Cd3(C16H9O7)2(C10H8N2)2(H2O)2]·2C3H7NO·5H2O}n, was obtained by the reaction of ether-linked 5-[(2-carboxyphenoxy)methyl]isophthalic acid (H3L) with CdII salts in the presence of 4,4'-bipyridine (bpy) under solvothermal conditions. In this complex, the CdII centres are connected by the carboxylate ligands to form two-dimensional wave-like layers, which are pillared by bpy ligands and extended into a rare three-dimensional (3,6)-connected sqc27 framework. The complex demonstrated good water stability and strong luminescence emissions. It not only possesses excellent luminescence sensing activities toward Fe3+ and Cr2O72- in aqueous solution, but can also distinguish between Cr2O72- and CrO42- by luminescence. Furthermore, it could be simply and quickly regenerated at least five times. A study of the sensing mechanism indicated that luminescence quenching may be related to the energy competition between the complex and sensing analytes.

Killing two birds with one stone: 2D+2D→3D parallel stacking and 3D self-penetrating structures in one reaction and their crystal-to-crystal transformation.

Reaction of the flexible phenolic carboxylate ligand 2-(3,5-dicarboxylbenzyloxy)benzoic acid (H3L) with nickel salts in the presence of 1,2-bis(pyridin-4-yl)ethylene (bpe) leads to the generation of a mixture of the two complexes under solvolthermal conditions, namely poly[[aqua[µ-1,2-bis(pyridin-4-yl)ethylene-κ2N:N']{µ-5-[(2-carboxyphenoxy)methyl]benzene-1,3-dicarboxylato-κ3O1,O1':O3}nickel(II)] dimethylformamide hemisolvate monohydrate], {[Ni(C16H10O7)(C12H10N2)(H2O)]·0.5C3H7NO·H2O}n or {[Ni(HL)(bpe)(H2O)]·0.5DMF·H2O}n, 1, and poly[[diaquatris[µ-1,2-bis(pyridin-4-yl)ethylene-κ2N:N']bis{µ-5-[(2-carboxyphenoxy)methyl]benzene-1,3-dicarboxylato-κ2O1:O5}nickel(II)] dimethylformamide disolvate hexahydrate], {[Ni2(C16H10O7)2(C12H10N2)3(H2O)2]·2C3H7NO·6H2O}n or {[Ni2(HL)2(bpe)3(H2O)2]·2DMF·6H2O}n, 2. In complex 1, the NiII centres are connected by the carboxylate and bpe ligands to form two-dimensional (2D) 4-connected (4,4) layers, which are extended into a 2D+2D→3D (3D is three-dimensional) supramolecular framework. In complex 2, bpe ligands connect to NiII centres to form 2D layers with Ni6(bpe)6 metallmacrocycles. Interestingly, 2D+2D→3D inclined polycatenation was observed between these layers. The final 5-connected 3D self-penetrating structure was generated through further connection of Ni-carboxylate chains with these inclined motifs. Both complexes were fully characterized by single-crystal analysis, powder X-ray diffraction analysis, FT-IR spectra, elemental analyses, thermal analysis and UV-Vis spectra. Notably, an interesting metal/ligand-induced crystal-to-crystal transformation was observed between the two complexes.

Tunable Light Emission and Multiresponsive Luminescent Sensitivities in Aqueous Solutions of Two Series of Lanthanide Metal-Organic Frameworks Based on Structurally Related Ligands.

Two series of lanthanide metal-organic frameworks (Ln-MOFs) from two structurally related flexible carboxylate-based ligands were solvothermally synthesized. H3L2 with additional -CH2- group provides more flexibility and different coordination modes and conformations compared with H3L1. As a result, 2-Ln MOFs are modulated from two-dimensional kgd of 1-Ln to three-dimensional rtl topological frameworks and further achieve enhanced chemical stability. The Eu- and Tb-MOFs exhibit strong fluorescent emission at the solid state because of the antenna effect of the ligands. Interestingly, the emissions can be tuned by simply doping Eu3+ and Tb3+ of different concentrations within the Eu xTb1- x MOFs. Notably, 2-Ln MOFs realize nearly white light emission by means of a trichromatic approach (red of Eu(III), green of Tb(III), and blue of the H3L2 ligand). Furthermore, 2-Ln MOFs also exhibit water stability and demonstrate high selective and sensitive sensing activities toward Fe(III) and Cr(VI) in aqueous solutions. The results further highlight the importance of the ligand flexibility on tuning MOF structures with improved structural stability and ion-sensing properties.

From 2D → 3D interpenetration to packing: N coligand-driven structural assembly and tuning of luminescent sensing activities towards Fe3+ and Cr2O72- ions.

Three new luminescent transition coordination polymers, namely, {[Cd(L)(4,4-bpy)]·DMF·H2O}n (1), {[Cd2(L)2(bpe)2]·3DMF·2.5H2O}n (2), and {[Cd(L)(bibp)]·2DMF}n (3), (H2L = 4,4'-[benzene-1,3-diylbis(methanediylsulfanediyl)]dibenzoic acid, 4,4-bpy = 4,4-bipyridine, bpe = 1,2-bis(4-pyridyl)ethylene, and bibp = 4,4'-bis(benzoimidazo-1-ly)biphenyl), were solvothermally synthesized using Cd2+ ions and S-containing dicarboxylate acid in the presence of different N coligands. These complexes were fully characterized via elemental analysis, infrared spectroscopy (IR), single crystal X-ray diffraction analysis, and thermal gravimetric analysis (TGA). Complexes 1-3 consist of 2-D structures through the connectivity of similar 1-D Cd-L chains by different N coligands. With an increase in the size of the N coligands, these complexes show structural changes from 2D → 3D with 3-fold interpenetration of complexes 1 and 2 to the 2-D packing modes of complex 3. The luminescence properties of these three complexes were studied in detail. The results reveal that each complex exhibits selectivity and sensitivity towards Fe3+ and Cr2O72- ions, and complex 2 demonstrates the lowest detection limit towards both ions.