Xing Rong

pH, solvent and metal ion induced octamolybdate-based metal–organic complexes decorated with a pyridyl-carboxylate ligand containing an amide group

Three octamolybdate-based metal–organic complexes constructed from a pyridyl-carboxylate ligand containing an amide group, 3-(2-pyridinecarboxylic acid)amido pyridine (HPCAP), namely, H2{[Cu3(PCAP)4(H2O)2](β-Mo8O26)}·10H2O (1), H{[Cu(PCAP)(H2O)](β-Mo8O26)0.5} (2) and H2[Co(H2O)6][Co2(PCAP)4(γ-Mo8O26)(H2O)2]·10H2O (3), have been successfully synthesized under hydrothermal or solvothermal (methanol–water mixed solvent) conditions. Single-crystal X-ray analyses reveal that compound 1 is a 2D layer based on infinite 1D [Cu3(PCAP)4]n2n+ chains and bidentate β-Mo8O264− anions. In compound 2, 1D “thin centipede” [Cu2(PCAP)2]n2n+ chains were connected by tetradentate β-Mo8O264− anions through the Cu–O bond to form a 2D network. In compound 3, γ-Mo8O264− anions were connected by adjacent [Co2(PCAP)4(H2O)2] moieties through Co–O and Mo–N bonds forming an uncommon 1D “fat centipede” chain. The adjacent chains were further extended to a 2D supramolecular network through hydrogen bonding interactions. The title compounds represent the first examples of introducing a pyridyl-carboxylate ligand containing an amide group into the POM system. The pH value, solvent and metal ions play key roles in the construction of the final architectures and show a great influence on the structural diversities of the title compounds. The electrochemical properties of compound 1 and the photocatalysis properties of the title compounds have been reported.

Diverse polyoxometalate-based metal–organic complexes constructed by a tetrazole- and pyridyl-containing asymmetric amide ligand or its in situ transformed ligand

By introducing a tetrazole- and pyridyl-containing asymmetric amide ligand into polyoxometalate (POM) systems, four POM-based complexes, namely, H4[Cu2(TAAP)4(H2O)](Mo8O26)2·20H2O (1), H2[Co(TAAP)2(H2O)2](Mo8O26)·11H2O (2), H2[Ag4(TAAP)4(H2O)2(PMo12O40)2]·4H2O (3), and H4[Ag2(AAP)4(PW12O40)2]·2AAP·12H2O (4) (TAAP = 3-(1H-tetrazole-1-acetic acid amido) pyridine; AAP = 3-(acetic acid amido) pyridine), have been prepared under solvothermal (methanol–water mixed solvent) or hydrothermal conditions and structurally characterized. Compounds 1 and 2 are isostructural 3D structures, which are based on 3D [M(TAAP)2]n2n+ metal–organic frameworks and noncoordinated [Mo8O26]4− polyanion templates. Compound 3 exhibits a dimeric structure constructed from two Keggin [PMo12O40]3− anions and a tetranuclear [Ag4(TAAP)4(H2O)2]4+ subunit. Compound 4 exhibits a 2D supramolecular network based on 1D infinite chains, which are constructed by [PW12O40]3− and Ag-AAP subunits. In compound 4, the AAP ligand was in situ transformed from TAAP. The structural diversities show that POMs play key roles in the construction of final architectures and the in situ transformation of TAAP. The title compounds represent the first examples of introducing tetrazole- and pyridyl-containing asymmetric amide ligand into the POM system. The electrochemistry, photocatalysis and photoluminescence properties of the title compounds have been reported.

Solvent-controlled synthesis of various Anderson-type polyoxometalate-based metal–organic complexes with excellent capacity for the chromatographic separation of dyes

By changing solvent systems, five new Anderson-type polyoxometalates (POMs)-based metal–organic complexes, namely, {(H2PCAP′)2[CrMo6(OH)5O19]}·H2O (1), {Cu3(PCAP)2[CrMo6(OH)5O19](H2O)3(DMF)2}·4H2O·2HCHO (2), {Cu3(PCAP)2[CrMo6(OH)6O18]Cl(H2O)5}·10H2O (3), {Co3(PCAP)2[CrMo6(OH)5O19](H2O)6}·9H2O·HCHO (4) and {Co3(HPCAP)2[CrMo6(OH)6O18]2(H2O)10}·7H2O·2CH3CH2OH (5) (HPCAP = 3-(2-pyridinecarboxylic acid amido)pyridine, PCAP′ = 3-(pyridinecarboxylic acid)amido pyridine), were successfully synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Complex 1 was obtained with H2O as the solvent and exhibited a 3D supramolecular network based on CrMo6 anions and protonated H2PCAP′ molecules via hydrogen bonds. It should be noted that the PCAP′ was in situ transformed from HPCAP. Complexes 2–5 were synthesized with different mixed solvents. In complex 2, the CrMo6 anions acted as an inorganic bridging ligand to link the 1D [Cu3(PCAP)2]n4n+ chains to construct a 2D layer. Complexes 3 and 4 showed similar 3D frameworks. Two orientations of metal–organic loops [M2(PCAP)2] (M = Cu for 3, Co for 4) could be observed, which directly extended the 1D M–CrMo6 chains into 3D networks with a 3,3,4,4-connected {42·123·14}{42·6}2 topology. In 5, the 1D Co–CrMo6 inorganic chain, [Co2(PCAP)2] binuclear loop unit and discrete CrMo6 polyanion were connected with each other by hydrogen-bonding interactions to form a 1D ladder-like supramolecular dual chain. The structural diversities showed that the solvents play key roles in the construction of various architectures and in the in situ transformation of HPCAP. The adsorption behaviours of the title complexes for organic dyes were investigated in detail. All of the title complexes showed an efficient adsorption capacity for the cationic dyes gentian violet (GV) and methylene blue (MB). In particular, complex 4 could selectively separate GV from the mixture of GV&RhB and GV&MO within 5–10 min, which can be used as a chromatography column for dye removal. In addition, the electrochemical properties of the title complexes were also studied.