Two luminescent Cd-MOFs were employed as dual-responsive luminescence sensors to detect acac and Cr2O72− through turn-on and turn-off mechanisms.

Three coordination complexes, {[Cd (HL) (bpea)center dot H2O]center dot H2O center dot DMF}(n) (1) ,{ [Cd (HL) (bpp)center dot H2O]center dot 2H(2)O center dot DMF}(n )(2) and {[Cd (Hl) (dmbpy)]center dot DMF}(n )(3) , were obtained from the reaction of 5-(3-carboxy-4-methoxybenzylamino) isophthalic acid (F1 3 L) with cadmium nitrate and different nitrogen-containing ligands under solvothermal conditions, and show interesting 2D -> 2D penetrating and 1D ribbon structures, respectively. The results reveal that these complexes all demonstrate luminescence quenching effect toward Cr2O72-, while only complex 1 shows a significant fluorescence enhancement in DMF solution of acetylacetone. The flexibility of carboxylate ligand and types and structures of nitrogen-containing ligands play an important role in regulating the structures and fluorescence properties of complexes.

By using the reduced Schiff base tricarboxylate ligand H(3)cip, one novel 3D Cd-based coordination polymer (Cd-CP) with the formula [Cd(Hcip)(bpea)(0.5)(H2O)](n) (H(3)cip = 5-(3-carboxybenzylamino)isophthalic acid, bpea = 1,2-bis(4-pyridyl)ethane) has been solvothermally synthesized. The prepared Cd-CP possesses a 4-connected CdSO4 net based on dinuclear {Cd-2} units. Luminescence measurements revealed that the complex exhibited ratiometric turn-on luminescence responses toward Al3+ and Cr3+ with a significant color change, which could be easily distinguished by the naked eye under ultraviolet light. Cd-CP can also respond to Fe3+ through a turn-off mechanism. Interestingly, the luminescence quenched by Fe3+@Cd-CP can be recovered and increased significantly by adding some competitive Al3+, while Cr3+ can only marginally increase the luminescence intensity of Fe3+@Cd-CP. Moreover, the detection of the three aforementioned metal ions can be realized by using Cd-CP-coated test papers, extending the potential application regions of the reported material to point-of-care tests and environmental field studies.

Based on a flexible ether-oxygen tricarboxylate ligand, H3L = 3,5-bis[(3-carboxylphenyl)oxy]benzoic acid, one novel 2-D La-CP with the formula of {[La(L)(H2O)(3)]center dot H2O}(n) has been solventhermally synthesized. The 2-D bilayer structure of La-CP is constructed by carboxylate-bridged La-n(CO2)(n) layers connected by M-shaped tricarboxylate ligands arranged below and above, respectively. The La-CP exhibits blue luminescence and demonstrates multi-responsive luminescence sensing activities toward Fe3+, Cr(VI) and benzothiazoles (BTs) through luminescence quenching. It could be repeated after at least five cycling runs. The fast response, high sensitivity and selectivity makes it a potential multi-functional chemosensor.

Two series of lanthanide metal organic frameworks (Ln-MOFs) from two structurally related flexible carboxylate-based ligands were solvothermally synthesized. H(3)L2 with additional -CH2- group provides more flexibility and different coordination modes and conformations compared with H(3)L1. 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 EuxTb1-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 H(3)L2 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 sensing properties.

Two 1-D lanthanide-based CPs (coordination polymers), Eu-CP and Tb-CP, have been solventhermally synthesized from a phenolic-linked tricarboxylate ligand 1,3,5-tri(2-carboxyphenoxy)benzene (H3L). Both complexes demonstrate stability and strong characteristic luminescence emissions in organic and water media. They also possess excellent luminescence sensing activities toward Fe3+ and Cr2O72−/CrO42− in DMF and aqueous solutions as well as simulated biological system. Notably, Tb-CP is one of the very few examples to effectively distinguish between CrO42− and Cr2O72− in aqueous and HEPES media. Both CPs could be simply and quickly regenerated at least five circles. The research on sensing mechanism indicated that the luminescence quenching may be related with the energy competition and weak interactions between CPs and sensing analytes.

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.