A Bioinspired Copper-Pair Catalyst in Metal-Organic Frameworks for Molecular Dioxygen Activation and Aerobic Oxidative C-N Coupling.

Open Cu sites were loaded to the UiO-67 metal-organic framework (MOF) skeleton by introduction of flexible Cu-binding pyridylmethylamine (pyma) side chains to the biphenyldicarboxylate linkers. Distance between Cu centers in the MOF pores was tuned by controlling the density of metal-binding side chains. "Interacted" Cu-pair or "isolated" monomeric Cu sites were achieved with high and low (pyma)Cu side chain loading, respectively. Spectroscopic and theoretical studies indicate that "interacted" Cu pairs can effectively bind and activate molecular dioxygen to form Cu2O2 clusters, which showed high catalytic activity for aerobic oxidative C-N coupling. On the contrary, MOF catalyst bearing isolated monomeric Cu sites only showed modest catalytic activity. Enhancement in catalytic performance for the Cu-pair catalyst is attributed to the remote synergistic effect of the paired Cu site, which binds molecular dioxygen and cleaves the O═O bond in a collaborative manner. This work demonstrates that noncovalently interacted metal-pair sites can effectively activate inert small molecules and promote heterogeneous catalytic processes.

A proton-conductive metal-organic framework based on imidazole and sulphate ligands.

A metal-organic framework (MOF) built from a combination of metal cations, neutral azole ligands and sulphate anions, [Cu2(DHBDI)3(SO4)2]n (1, DHBDI = 1H,5H-benzo[1,2-d:4,5-d']diimidazole), was synthesized. MOF 1 exhibits good chemical stability in acids, bases and boiling water while showing high hydrophilicity. Meanwhile, MOF 1 exhibits a proton conductivity of 1.14 × 10-3 S cm-1 at 90 °C and 98% RH, among the best for MOF materials with uncoordinated N sites. Temperature-dependent conductivity measurements suggest a vehicle mechanism (Ea = 0.64 eV) for proton transport.

Novel 3D Semiconducting Open-Frameworks based on Cuprous Bromides with Visible Light Driven Photocatalytic Properties.

Visible light driven photocatalysts based on crystalline microporous metal halogenides received much less attention compared with dense or composite oxide semiconductors. Using the well-known photosensitive transition metal-complexes [TM(2,2-bipy)3 ]2+ (TM=Fe, Co, Ni, Ru) as templates, a special three-dimensional (3D) metal halogenide framework of [TM(2,2-bipy)3 ]Cu4 Br6 was designed with [Cu4 Br4 ] cluster as 4-connected node. These microporous materials feature narrow band gaps and stable visible light driven photocatalytic properties including water reduction to provide H2 and photodegradation of organic pollutants. The study of electronic band structure shows that the TM complexes effectively prevent the recombination of photo-induced electron/hole pairs leading to excellent photocatalytic activity and photochemical stability. This work represents the first 3D microporous metal halogenides used as visible light driven photocatalyst to provide hydrogen energy.

Novel Three-Dimensional Semiconducting Materials Based on Hybrid d10 Transition Metal Halogenides as Visible Light-Driven Photocatalysts.

The development of new visible light-driven photocatalysts based on semiconducting materials remains a greatly interesting and challenging task for the purpose of solving the energy crisis and environmental issues. By using photosensitive [(Me)2-2,2'-bipy]2+ (1,1'-dimethyl-2,2'-bipyridinium) cation as template, we synthesized one new type of inorganic-organic hybrid cuprous and silver halogenides of [(Me)2-2,2'-bipy]M8X10 (M = Cu, Ag, X = Br, I). The compounds feature a three-dimensional anionic [M8X10]2- network composed of a one-dimensional [M8X12] chain based on MX4 tetrahedral units. The photosensitization of organic cationic templates results in narrow band gaps of hybrid compounds (1.66-2.06 eV), which feature stable visible light-driven photodegradation activities for organic pollutants. A detailed study of the photocatalytic mechanism, including the photoelectric response, photoluminescence spectra, and theoretical calculations, shows that the organic cationic template effectively inhibits the recombination of photoinduced electron-hole pairs leading to excellent photocatalytic activities and photochemical stabilities.

Transition metal complex directed lead bromides with tunable structures and visible light driven photocatalytic properties.

With similar transition metal (TM) complex cations as structural directing agents (SDAs), six new hybrid lead bromides were synthesized and structurally characterized as [Co(2,2-bipy)3]2{[Co(2,2-bipy)]3Pb7Br24} (1), [Co(2,2-bipy)2Br]PbBr3 (2), [TM(phen)3]Pb2Br6 (TM = Co (3) and Ni (4)), [Co(2,2-bipy)3]Pb3Br9 (5) and [Co(2,2-bipy)3]Pb5Br13·CH3CN (6) with distinct structural types from zero-dimensional (0D) unit, one-dimensional (1D) chain to two-dimensional (2D) layer. Compound 1 contains the 0D {[Co(bipy)]3Pb7Br24}4- units built from the [Pb7Br24] ring attached by three unsaturated [Co(2,2-bipy)]2+ complexes via Co-Br bonds. Under the direction actions of different SDAs, compounds 2 and 3-4 contain two different types of [Pb2Br6]4- chains based on the same octahedral [PbBr6] units but with distinct connecting manners, respectively. Using the same [Co(2,2-bipy)3]3+ as SDA, compound 5 reveals a 1D [Pb3Br9]3- double chain, whereas compound 6 features a 2D complex [Pb5Br13]3- layer. The UV/vis diffuse-reflectance measurements reveal that the title compounds feature tunable band gaps of 1.70-2.29 eV. Under the visible light irradiation, sample 6 exhibits efficient and stable photocatalytic degradation activities over organic pollutants, which mainly originates from the multi-electronic effects of the TM complex cations. A possible photocatalytic mechanism is also proposed based on the radical trapping experiments and electronic band structural calculations.