Anion-Directed Assemblies of Cationic Metal–Organic Frameworks Based on 4,4′-Bis(1,2,4-triazole): Syntheses, Structures, Luminescent and Anion Exchange Properties

Three cationic metal–organic frameworks (MOFs), Ag­(btr)·​PF₆·​0.5CH₃CN (<b>1</b>), Ag₂(btr)₂­(H₂O)·​2CF₃SO₃·​H₂O (<b>2</b>), and Ag₂(btr)₂­(NO₃)·​NO₃ (<b>3</b>), were prepared from reaction of 4,4′-bis­(1,2,4-triazole) (btr) with silver salts containing different anions. Complex <b>1</b> is a three-dimensional (3-D) framework constructed from tetrahedral-shaped nanoscale coordination cages with PF₆^– as counteranions. <b>2</b> and <b>3</b> are 3-D architectures containing 1-D channels, in which charge-balancing CF₃SO₃^– and NO₃^– are located in their respective channels. Luminescent emission of <b>1</b>–<b>3</b> shows an obvious red shift compared with the btr ligand. Anion exchange studies show that <b>1</b> is able to selectively exchange MnO₄^– in aqueous solution with a modest capacity of 0.56 mol mol^–1; the luminescent emission of <b>1</b> is quickly quenched upon MnO₄^– exchange

Imidazolium-Based Porous Organic Polymers: Anion Exchange-Driven Capture and Luminescent Probe of Cr₂O₇^2–

A series of imidazolium-based porous organic polymers (POP-Ims) was synthesized through Yamamoto reaction of 1,3-bis­(4-bromophenyl)­imidazolium bromide and tetrakis­(4-bromophenyl)­ethylene. Porosities and hydrophilicity of such polymers may be well tuned by varying the ratios of two monomers. POP-Im with the highest density of imidazolium moiety (POP-Im1) exhibits the best dispersity in water and the highest efficiency in removing Cr₂O₇^2–. The capture capacity of 171.99 mg g^–1 and the removal efficiency of 87.9% were achieved using an equivalent amount of POP-Im1 within 5 min. However, no Cr₂O₇^2– capture was observed using nonionic analogue despite its large surface area and abundant pores, suggesting that anion exchange is the driving force for the removal of Cr₂O₇^2–. POP-Im1 also displays excellent enrichment ability and remarkable selectivity in capturing Cr₂O₇^2–. Cr­(VI) in acid electroplating wastewater can be removed completely using excess POP-Im1. In addition, POP-Im1 can serve as a luminescent probe for Cr₂O₇^2– due to the incorporation of luminescent tetraphenylethene moiety

Substituent Effects of Isophthalate Derivatives on the Construction of Zinc(II) Coordination Polymers Incorporating Flexible Bis(imidazolyl) Ligands

Eight Zn­(II) coordination polymers, [Zn­(EtO-ip)­(bimb)]_<i>n</i>­(DMF)_<i>n</i> (<b>1</b>), [Zn­(PrO-ip)­(bimb)_0.5]_<i>n</i> (<b>2</b>), [Zn₂(NO₂-ip)₂<b>­(</b>bimb)₂]_<i>n</i>­(H₂O)_<i>n</i> (<b>3</b>), [Zn₂(NO₂-ip)₂­(bimb)_1.5]_<i>n</i>­(H₂O)_<i>n</i> (<b>4</b>), [Zn­(MeO-ip)­(bmib)_0.5]_<i>n</i>­(H₂O)_0.5<i>n</i> (<b>5</b>), [Zn­(EtO-ip)­(bmib)_0.5]_<i>n</i> (<b>6</b>), [Zn­(PrO-ip)­(bmib)]<i>_n</i> (<b>7</b>), and [Zn (NO₂-ip)­(bmib)]<i>_n</i> (<b>8</b>) (EtO-ip = 5-ethoxyisophthalate, PrO-ip = 5-propoxyisophthalate, NO₂-ip = 5-nitroisophthalate, MeO-ip = 5-methoxy­isophthalate, bimb = 1,4-bis­(imidazol-1′-yl)­butane, bmib = 1,4-bis­(2-methyl­imidazol-1′-yl)­butane), have been prepared and characterized by single-crystal X-ray diffraction analyses. In <b>1</b>, bis-monodentate EtO-ip and <i>exo</i>-bidentate bimb connect four-coordinated Zn­(II) into a corrugated 2-D layer. In <b>2</b>, μ₂,η²-carboxylate and monodentate carboxylate in PrO-ip bridge dinuclear Zn­(II) units to generate a [Zn₂(PrO-ip)₄]_<i>n</i> layer, which is further extended by bimb into a 3-D network. Interestingly, bis-monodentate NO₂-ip and bimb in <b>3</b> connect four-coordinated Zn­(II) into two independent 2-D layers, which are stabilized by π···π stacking interactions from phenyl rings of NO₂-ip in different layers. In <b>4</b>, μ₃-bridged NO₂-ip alternately links single Zn­(II) ions and dinuclear Zn­(II) units into a 1-D chain containing square-shaped cavities, which is further extended by bimb into a 2-fold interpenetrating 3-D framework. However, μ₃-bridged MeO-ip and EtO-ip together with bmib in <b>5</b> and <b>6</b> link dinuclear Zn­(II) units into a 2-D layer. In <b>7</b>, bis-monodentate PrO-ip and bmib connect four-coordinated Zn­(II) ions into a 2-D corrugated layer, while four-coordinated Zn­(II) ions in <b>8</b> are linked by bis-monodentate NO₂-ip and bmib into a 3-fold interpenetrating framework consisting of left- and right-handed helical chains. The thermal stability and luminescent properties of <b>1</b>–<b>8</b> in the solid state were investigated in detail

Porous Cadmium(II) Anionic Metal–Organic Frameworks Based on Aromatic Tricarboxylate Ligands: Encapsulation of Protonated Flexible Bis(2-methylimidazolyl) Ligands and Proton Conductivity

Two porous 3-D anionic metal–organic frameworks (MOFs) containing protonated bmib, [Cd₂(btc)₂(H₂O)₂]_<i>n</i>·<i>n</i>(H₂bmib)·6<i>n</i>(H₂O) (<b>1</b>) and [Cd₄(cpip)₂(Hcpip)₂]_<i>n</i>·<i>n</i>(H₂bmib)·<i>n</i>(H₂O) (<b>2</b>), have been prepared by hydrothermal reactions of Cd­(NO₃)₂·4H₂O, 1,4-bis­(2-methylimidazol-1′-yl)­butane (bmib) with 1,3,5-benzenetricarboxylic acid (H₃btc) and 5-(4-carboxyphenoxy)­isophthalic acid (H₃cpip), respectively. Complexes <b>1</b> and <b>2</b> are 3-D anionic frameworks containing 1-D channels and consisting of tetranuclear Cd­(II)-carboxylate units, respectively. H₂bmib and lattice water molecules are located in their void spaces and form extensive hydrogen bonds and C–H···π interaction with the anionic frameworks. TGA studies and XRD patterns show the anionic frameworks of <b>1</b> and <b>2</b> are intact after the removal of lattice water molecules. The luminescent emission of <b>1</b> and <b>2</b> shows an obvious red shift in comparison with free H₃btc and H₃cpip, respectively. Complexes <b>1</b> and <b>2</b> possess proton conduction owing to the presence of the extensive hydrogen bonds and protonation of bmib; their proton conductivity at 333 K and 95% relative humidity are 5.4 × 10^–5 and 2.2 × 10^–5 S cm^–1, respectively