Honghan Fei

Enhanced Photochemical Hydrogen Production by a Molecular Diiron Catalyst Incorporated into a Metal–Organic Framework

A molecular proton reduction catalyst [FeFe](dcbdt)(CO)6 (1, dcbdt = 1,4-dicarboxylbenzene-2,3-dithiolate) with structural similarities to [FeFe]-hydrogenase active sites has been incorporated into a highly robust Zr(IV)-based metal–organic framework (MOF) by postsynthetic exchange (PSE). The PSE protocol is crucial as direct solvothermal synthesis fails to produce the functionalized MOF. The molecular integrity of the organometallic site within the MOF is demonstrated by a variety of techniques, including X-ray absorption spectroscopy. In conjunction with [Ru(bpy)3]2+ as a photosensitizer and ascorbate as an electron donor, MOF-[FeFe](dcbdt)(CO)6 catalyzes photochemical hydrogen evolution in water at pH 5. The immobilized catalyst shows substantially improved initial rates and overall hydrogen production when compared to a reference system of complex 1 in solution. Improved catalytic performance is ascribed to structural stabilization of the complex when incorporated in the MOF as well as the protection of reduced catalysts 1– and 12– from undesirable charge recombination with oxidized ascorbate.

Metalation of a Thiocatechol-Functionalized Zr(IV)-Based Metal–Organic Framework for Selective C–H Functionalization

The incorporation of 2,3-dimercaptoterephthalate (thiocatecholate, tcat) into a highly robust UiO-type metal-organic framework (MOF) has been achieved via postsynthetic exchange (PSE). The anionic, electron-donating thiocatecholato motif provides an excellent platform to obtain site-isolated and coordinatively unsaturated soft metal sites in a robust MOF architecture. Metalation of the thiocatechol group with palladium affords unprecedented Pd-mono(thiocatecholato) moieties within these MOFs. Importantly, Pd-metalated MOFs are efficient, heterogeneous, and recyclable catalysts for regioselective functionalization of sp(2) C-H bond. This material is a rare example of chelation-assisted C-H functionalization performed by a MOF catalyst.

A New Paradigm for Anion Trapping in High Capacity and Selectivity: Crystal-to-Crystal Transformation of Cationic Materials

We describe a new methodology to the selective trapping of priority pollutants that occur inherently as oxo-anions (e.g., perchlorate, chromate, arsenate, pertechnetate, etc.) or organic anions (e.g., salicylate, pharmaceuticals, and their metabolites, which are often chlorinated into potentially more harmful compounds). The typical approach to trapping anions is exchange into cationic hosts such as resins or layered double hydroxides. Both capacity and selectivity are limited by the equilibrium of the process and moreover are often subject to interference, e.g. by carbonate that is always present in water from atmospheric CO(2). Our approach takes advantage of the metastability of our cationically charged materials to instead trap by recrystallization to a new structure. Exceptionally high adsorption capacities for permanganate and perrhenate--studied as models for pertechnetate--were found for a Ag(I)-based cationic extended framework. The exchange capacity reached 292 and 602 mg/g, respectively, over five times the exchange capacity compared to conventional layered double hydroxides. Our cationic material can also selectively trap these and other toxic oxo-anions when nontoxic anions (e.g., nitrate, carbonate) were present in an over 100-fold excess concentration.

Copper Hydroxide Ethanedisulfonate: A Cationic Inorganic Layered Material for High‐Capacity Anion Exchange

Many inorganic pollutants in the form of metal oxo-hydroxo anions are listed as EPA (U.S. Environmental Protection Agency) priority pollutants. Recently, EPA set a national limit for perchlorate (ClO4 , a widespread anion occurring from rocket fuel, fireworks and other sources) in drinking water. Chromate (CrO4 2 ) and pertechnetate (TcO4 ) are also problematic monomeric oxo anions, in this case upon the vitrification of radioactive waste. 4] Meanwhile, pharmaceuticals and their metabolites have gained increasing attention as pollutants, many existing as organic anions at neutral pH. Current treatment processes are insufficient to adsorb them in high capacity and at reasonable cost. Chlorination can lead to even more toxic compounds, such as monohalogenated or oxidized by-products. The typical approach to trap these intrinsically anionic pollutants remains ion exchange resins, though these organic polymers possess limited thermal and chemical stability and thus longevity. Cationic inorganic layered materials are 2-D extended architectures where the positively charged layers are held together electrostatically by charge-balancing anions. One typical and widely studied example is the layered double hydroxides (LDHs) with general formula [M1 xM 3+ x(OH)2] [A x/n·mH2O], where M 2+ and M are a range of metals (e.g. Mg and Al), x is the ratio of M/(M+M), and A are n-valent interlamellar anions (e.g. CO3 2 ). 9] Copper-containing LDHs with a second transition or main-group metal are difficult to synthesize but have been shown to catalyze benzene oxidation. Also known as hydrotalcites, LDHs are considered plausible alternatives to resins and can exchange many inorganic and organic anions reversibly. Their selectivity towards toxic anions over carbonate and other interfering anions, however, limits adsorption capacities and thus potential application in water purification. Indeed, this class of materials often requires calcination pre-treatment before ion exchange and displays difficulty in recovery and reuse. Our group has reported a series of cationic layered inorganic materials consisting of lower p-block metal fluoride and oxide-hydroxide layers charge-balanced by nitrate, perchlorate or alkanedisulfonate. Attempts to anion exchange the interlamellar anions for toxic pollutants, however, were either unsuccessful or led to decomposition of the host layers. Meanwhile, layered rare earth hydroxides are an emerging class of inorganic materials with halide, nitrate or other anions in the interlayer region. In addition, two three-dimensional cationic inorganic extended frameworks were also reported last year. The structures are based on thorium and ytterbium, charge-balanced by borate and chloride, respectively. 22] The structures exchange for several smaller anions to 72 %, though excess solid was required. Unlike metal-organic frameworks, no investigation has been made on synthesis of cationic inorganic extended materials based on the less toxic, lower cost and more chemically understood first row transition metals. Herein, we report the successful synthesis and crystallographic characterization of the first example beyond LDHs of a copper based cationic inorganic material. [Cu4(OH)6] [O3SCH2CH2SO3]·2H2O (which we denote SLUG-26, University of California, Santa Cruz, Structure No. 26) possesses high thermal and chemical stability. Infinite M–O–M 2-D inorganic connectivity results in a rare cationic copper hydroxide layer. This first non-LDH copper hydroxide cationic inorganic extended structure displays rich anion intercalation chemistry, with exchange for variable-length a,w-alkanedicarboxylates and anion pollutant trapping properties. SLUG-26 was synthesized under hydrothermal conditions with pure phase at optimized conditions (see Experimental Section). Synthesis temperature higher than the ideal 150 8C (160 8C to 180 8C) resulted in CuO (PDF-ICDD #98-0000429) as the majority phase. Lower temperature (< 125 8C) produced either clear solution or lower yield of the product. Excess 1,2-ethanedisulfonate (EDS) with a molar ratio of 1:4 for copper nitrate to disodium ethanedisulfonate was necessary, since lower molar ratios (1:1 to 1:2) gave no solid product. Presence of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was also necessary for crystal formation, which is known to facilitate rod-like crystal growth. The high yield and phase purity was supported by experimental powder X-ray diffraction (PXRD) matching well with the theoretical pattern simulated from single-crystal data (Supporting Information, Figure S1). [*] H. Fei, Prof. S. R. J. Oliver Department of Chemistry and Biochemistry University of California, Santa Cruz 1156 High Street, Santa Cruz, CA 95064 (USA) E-mail: soliver@ucsc.edu Homepage: http://chemistry.ucsc.edu/faculty/oliver.html

Anion exchange of the cationic layered material [Pb2F2]2+.

We demonstrate the complete exchange of the interlamellar anions of a 2-D cationic inorganic material. The α,ω-alkanedisulfonates were exchanged for α,ω-alkanedicarboxylates, leading to two new cationic materials with the same [Pb(2)F(2)](2+) layered architecture. Both were solved by single crystal X-ray diffraction and the transformation also followed by in situ optical microscopy and ex situ powder X-ray diffraction. This report represents a rare example of metal-organic framework displaying highly efficient and complete replacement of its anionic organic linker while retaining the original extended inorganic layer. It also opens up further possibilities for introducing other anions or abatement of problematic anions such as pharmaceuticals and their metabolites.

Hydrothermal Synthesis of Two Cationic Bismuthate Clusters: An Alkylenedisulfonate Bridged Hexamer, [Bi6O4(OH)4(H2O)2][(CH2)2(SO3)2]3 and a Rare Nonamer Templated by Triflate, [Bi9O8(OH)6][CF3SO3]5

This paper reports the synthesis, characterization, and application of two cationic bismuthate clusters by anion templating. The compounds were synthesized under mild hydrothermal treatment and characterized by powder and single-crystal X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The first material consists of a cationic hexanuclear bismuthate cluster octahedral in geometry and linked by 1,2-ethanedisulfonate molecules. This structure is thermally stable to about 235 degrees C. In the second compound, discrete cationic nonanuclear bismuthate clusters interact electrostatically with trifluoromethanesulfonate anions to pack into a nearly layered assembly. The material undergoes a transformation to Bi(2)O(3) upon loss of the triflate groups at about 385 degrees C. Both materials demonstrate the use of sulfonate groups for the anion-directed assembly of these rare cationic inorganic structures. The application of the 3D octahedral bismuth cluster material toward acidic heterogeneous catalysis is also reported.

Polymer Gel Templating of Free-Standing Inorganic Monoliths for Photocatalysis

We have developed a simple, low-cost process to fabricate free-standing porous metal oxide monoliths. Various swollen polymers and hydrogels possessing an open network structure are infiltrated with pure liquid metal alkoxide. Hydrolysis followed by chemical or thermal degradation of the polymer leads to bulk porous monoliths, TiO2 and SiO2 as initial examples. The titania solids were subsequently employed as photocatalysts under UV light and monitored for adsorption. The materials show efficient reusable photocatalytic ability as compared to pure-phase nanoparticle titanium oxide.

Erbium hydroxide ethanedisulfonate: a cationic layered material with organic anion exchange capability.

We describe a cationic erbium-based material [Er12(OH)29(H2O)5][O3SCH2CH2SO3]3.5·5H2O. As synthesized, the material is water stable and capable of complete organic anion exchange for a variety of α,ω-alkanedicarboxylates. We chose these anions as initial examples of exchange and as an analog for pharmaceutical waste, some of which have a carboxylate functionality at neutral pH range. Free-floating and partially anchored organosulfonate anions reside between the cationic corrugated layers and allow for exchange. The structure also displays a reversible hydration event above 100 °C. Both the as-synthesized and the exchanged materials are characterized by a variety of analytical techniques.

A Cationic Antimonite Chain Templated by Sulfate: [Sb6O74+][(SO42–)2]

An extended metal oxide possessing a cationic charge on the host has been synthesized by hydrothermal methods. The structure consists of 1D antimony oxide [Sb(6)O(7)](4+) chains with a new structural motif of four Sb atoms wide and unprotonated sulfate anions between the chains. The material was characterized by powder and single-crystal X-ray diffraction. Thermal behavior and chemical resistance in aqueous acidic conditions (pH ~2) indicate a highly stable cationic material. The stability is attributed to the entirely inorganic composition of the structure, where 1D covalently extended chains are electrostatically bound to divalent anions.

Synthesis and magnetic properties of a 3-D nickel hydroxide capped by succinate

We have successfully synthesized a rare example of an open framework nickel oxide with succinate capping the channels. A honeycomb-like layer of 14-membered rings centered in the (11) plane are connected by vertex-sharing NiO6 octahedra and water resides in the channels. The structure is only the second example of an extended inorganic–organic hybrid material containing 3-D Ni–O–Ni connectivity and was structurally characterized by single-crystal and powder X-ray diffraction. The material displays excellent chemical stability in aqueous solution from pH ∼ 1 to 13 and thermal stability to ∼375 °C as evidenced by thermogravimetric analysis coupled mass spectroscopy. The Ni2+ ions order ferromagnetically below Tc = 5.1 K and anisotropic exchange interactions lead to a field-induced metamagnetic transition and spin-glass-like dependence on cooling conditions in magnetic field.