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It is of considerable interest to prepare weakly ligated, labile ligand (WLLL) nanoparticles for applications in areas such as chemical catalysis. WLLL nanoparticles can be defined as nanoparticles with sufficient, albeit minimal, surface ligands of moderate binding strength to meta-stabilize nanoparticles, initial stabilizer ligands that can be readily replaced by other, desired, more strongly coordinating ligands and removed completely when desired. Herein, we describe WLLL nanoparticles prepared from [Ir(1,5-COD)Cl]2 reduction under H2, in acetone. The results suggest that H+Cl–-stabilized Ir(0)n nanoparticles, herein Ir(0)n·(H+Cl–)a, serve as a WLLL nanoparticle for the preparation of, as illustrative examples, five specific nanoparticle products: Ir(0)n·(Cl–Bu3NH+)a, Ir(0)n·(Cl–Dodec3NH+)a, Ir(0)n·(POct3)0.2n(Cl–H+)b, Ir(0)n·(POct3)0.2n, and the γ-Al2O3-supported heterogeneous catalyst, Ir(0)n·(γ-Al2O3)a(Cl–H+)b. (where a and b vary for the differently ligated nanoparticles; in addition, solvent can ...

Porphyrins are important molecules widely found in nature in the form of enzyme active sites and visible light absorption units. Recent interest in using these functional molecules as building blocks for the construction of metal-organic frameworks (MOFs) have rapidly increased due to the ease in which the locations of, and the distances between, the porphyrin units can be controlled in these porous crystalline materials. Porphyrin-based MOFs with atomically precise structures provide an ideal platform for the investigation of their structure-function relationships in the solid state without compromising accessibility to the inherent properties of the porphyrin building blocks. This review will provide a historical overview of the development and applications of porphyrin-based MOFs from early studies focused on design and structures, to recent efforts on their utilization in biomimetic catalysis, photocatalysis, electrocatalysis, sensing, and biomedical applications.

In 2010 we reported a two-step synthesis of a Ir0∼900/γ-Al2O3 supported-nanoparticle catalyst. In that study, a well-defined Ir(1,5-COD)Cl/γ-Al2O3 precatalyst was isolated and characterized before being reduced in contact with acetone solvent and cyclohexene and under H2 in a second step. Synthetically, one would like to remove the Ir(1,5-COD)Cl/γ-Al2O3 precatalyst isolation step, shortening the precatalyst synthesis and allowing the overall synthesis to be accomplished more efficiently in one pot. However, herein we report that the one-pot synthesis starting from commercially available [Ir(1,5-COD)Cl]2 and γ-Al2O3 yields an order of magnitude increase in the observed nucleation rate constant, k1,obs, as well as a decrease in the average particle size from Ir0∼900 to Ir0∼600. Mechanistic experiments reveal that the origin of this effect, amazingly, is the presence of residual ethyl acetate employed in the isolated precatalyst synthesis, which is not present in the one-pot synthesis. Additional mechanistic...

The rapid destruction of chemical threats, such as phosphate-based nerve agents, is of considerable current interest. The hydrolysis of the nerve-agent simulant methylparaoxon, as catalyzed by UiO-66 and UiO-67, was examined as a function of pH. Surprisingly, even though typical phosphate–ester hydrolysis mechanisms entail nucleophilic attack of the simulant by aqueous hydroxide, the rate of hydrolysis accelerates as the solution pH is lowered. The unexpected behavior is attributed to a pH-dependent composition change followed by ligand substitution at the Zr6-based node.

Chemical warfare agents containing phosphonate ester bonds are among the most toxic chemicals known to mankind. Recent global military events, such as the conflict and disarmament in Syria, have brought into focus the need to find effective strategies for the rapid destruction of these banned chemicals. Solutions are needed for immediate personal protection (for example, the filtration and catalytic destruction of airborne versions of agents), bulk destruction of chemical weapon stockpiles, protection (via coating) of clothing, equipment and buildings, and containment of agent spills. Solid heterogeneous materials such as modified activated carbon or metal oxides exhibit many desirable characteristics for the destruction of chemical warfare agents. However, low sorptive capacities, low effective active site loadings, deactivation of the active site, slow degradation kinetics, and/or a lack of tailorability offer significant room for improvement in these materials. Here, we report a carefully chosen metal-organic framework (MOF) material featuring high porosity and exceptional chemical stability that is extraordinarily effective for the degradation of nerve agents and their simulants. Experimental and computational evidence points to Lewis-acidic Zr(IV) ions as the active sites and to their superb accessibility as a defining element of their efficacy.

An isoreticular series of metal-organic frameworks (MOFs) with the ftw topology based on zirconium oxoclusters and tetracarboxylate linkers with a planar core (NU-1101 through NU-1104) has been synthesized employing a linker expansion approach. In this series, NU-1103 has a pore volume of 2.91 cc g(-1) and a geometrically calculated surface area of 5646 m(2) g(-1), which is the highest value reported to date for a zirconium-based MOF and among the largest that have been reported for any porous material. Successful activation of the MOFs was proven based on the agreement of pore volumes and BET areas obtained from simulated and experimental isotherms. Critical for practical applications, NU-1103 combines for the first time ultrahigh surface area and water stability, where this material retained complete structural integrity after soaking in water. Pressure range selection for the BET calculations on these materials was guided by the four so-called "consistency criteria". The experimental BET area of NU-1103 was 6550 m(2) g(-1). Insights obtained from molecular simulation suggest that, as a consequence of pore-filling contamination, the BET method overestimates the monolayer loading of NU-1103 by ∼16%.

The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO2 and UiO-66-(OH)2 showed little to no change in hydrolysis rate. However, UiO-66-NH2 showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe2 and UiO-67-NH2. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH2 is a faster catalyst than UiO-67 and UiO-67-NMe2. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.

Metal-organic frameworks (MOFs) constructed from Zr6-based nodes have recently received considerable attention given their exceptional thermal, chemical, and mechanical stability. Because of this, the structural diversity of Zr6-based MOFs has expanded considerably and in turn given rise to difficulty in their precise characterization. In particular it has been difficult to assign where protons (needed for charge balance) reside on some Zr6-based nodes. Elucidating the precise proton topologies in Zr6-based MOFs will have wide ranging implications in defining their chemical reactivity, acid/base characteristics, conductivity, and chemical catalysis. Here we have used a combined quantum mechanical and experimental approach to elucidate the precise proton topology of the Zr6-based framework NU-1000. Our data indicate that a mixed node topology, [Zr6(μ3-O)4(μ3-OH)4(OH)4 (OH2)4](8+), is preferred and simultaneously rule out five alternative node topologies.

A metal–organic framework (MOF) with high volumetric deliverable capacity for methane was synthesized after being identified by computational screening of 204 hypothetical MOF structures featuring (Zr6O4)(OH)4(CO2)n inorganic building blocks. The predicted MOF (NU-800) has an fcu topology in which zirconium nodes are connected via ditopic 1,4-benzenedipropynoic acid linkers. Based on our computer simulations, alkyne groups adjacent to the inorganic zirconium nodes provide more efficient methane packing around the nodes at high pressures. The high predicted gas uptake properties of this new MOF were confirmed by high-pressure isotherm measurements over a large temperature and pressure range. The measured methane deliverable capacity of NU-800 between 65 and 5.8 bar is 167 cc(STP)/cc (0.215 g/g), the highest among zirconium-based MOFs. High-pressure uptake values of H2 and CO2 are also among the highest reported. These high gas uptake characteristics, along with the expected highly stable structure of NU-80...

Metal-organic frameworks (MOFs) are hybrid porous materials with many potential applications, which intimately depend on the presence of chemical functionality either at the organic linkers and/or at the metal nodes. Functionality that cannot be introduced into MOFs directly via de novo syntheses can be accessed through post-synthesis modification (PSM) on the reactive moieties of the linkers and/or nodes without disrupting the metal-linker bonds. Even more intriguing methods that go beyond PSM are herein termed building block replacement (BBR) which encompasses (i) solvent-assisted linker exchange (SALE), (ii) non-bridging ligand replacement, and (iii) transmetalation. These one-step or tandem BBR processes involve exchanging key structural components of the MOF, which in turn should allow for the evolution of protoMOF structures (i.e., the utilization of a parent MOF as a template) to design MOFs composed of completely new components, presumably via single crystal to single crystal transformations. The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided. Future perspectives providing a glimpse into how these techniques can lead to various unexplored areas of MOF chemistry are also presented.

Metall-organische Geruste (MOFs) sind Hybridmaterialien, die anhaltendes Interesse auf sich ziehen – nicht zuletzt wegen vielfaltiger moglicher Anwendungen, von der Gastrennung uber die Katalyse bis hin zum Sammeln von Licht. Allerdings ist die De-novo-Synthese von MOFs mit gewunschten Eigenschaften nicht immer einfach: unerwunschte Topologien konnen entstehen, die Loslichkeit von Vorstufen kann zu gering sein, und die Funktionalitat wichtiger Netzwerkkomponenten kann verlorengehen. Mit einem neuen Ansatz – dem losungsmittelunterstutzten Linker-Austausch (“solvent-assisted linker exchange”, SALE) – lassen sich diese Probleme umgehen, und tatsachlich wurden mit SALE bereits verschiedene MOF-Materialien erzeugt, die durch direkte Syntheseverfahren nicht erhaltlich waren. Unsere Ubersicht beschreibt Forschungsergebnisse uber MOFs, die erst durch SALE moglich gemacht wurden, und diskutiert Studien, die das Verstandnis dieses Verfahrens verbessert und sein Anwendungsgebiet erweitert haben.

Solvent-assisted linker exchange (SALE) has recently emerged as an attractive strategy for the synthesis of metal-organic frameworks (MOFs) that are unobtainable via traditional synthetic pathways. Herein we present the first example of selective SALE in which only the benzimiadazolate-containing linkers in a series of mixed-linker zeolitic imidazolate frameworks (ZIF-69, -78, and -76) are replaced. The resultant materials (SALEM-10, SALEM-10b, and SALEM-11, respectively) are isostructural to the parent framework and in each case contain trifluoromethyl moieties. We therefore evaluated each of these materials for their hydrophobicity in condensed and gas phases. We expect that selective SALE will significantly facilitate the design of improved, and potentially complex, MOF materials with new and unusual properties.

Product stoichiometry, particle-size defocusing, and kinetic evidence are reported consistent with and supportive of a four-step mechanism of supported transition-metal nanoparticle formation in contact with solution: slow continuous nucleation, A → B (rate constant k1), autocatalytic surface growth, A + B → 2B (rate constant k2), bimolecular agglomeration, B + B → C (rate constant k3), and secondary autocatalytic surface growth, A + C → 1.5C (rate constant k4), where A is nominally the Ir(1,5-COD)Cl/γ-Al2O3 precursor, B the growing Ir(0) particles, and C the larger, catalytically active nanoparticles. The significance of this work is at least 4-fold: first, this is the first documentation of a four-step mechanism for supported-nanoparticle formation in contact with solution. Second, the proposed four-step mechanism, which was obtained following the disproof of 18 alternative mechanisms, is a new four-step mechanism in which the new fourth step is A + C → 1.5C in the presence of the solid, γ-Al2O3 support. Third, the four-step mechanism provides rare, precise chemical and kinetic precedent for metal particle nucleation, growth, and now agglomeration (B + B → C) and secondary surface autocatalytic growth (A + C → 1.5C) involved in supported-nanoparticle heterogeneous catalyst formation in contact with solution. Fourth, one now has firm, disproof-based chemical-mechanism precedent for two specific, balanced pseudoelementary kinetic steps and their precise chemical descriptors of bimolecular particle agglomeration, B + B → C, and autocatalytic agglomeration, B + C → 1.5C, involved in, for example, nanoparticle catalyst sintering.

A uniform and crack-free metalorganic framework (MOF) thin film composed of free-standing acicular nanorods was grown on a transparent conducting glass substrate. The MOF thin film exhibits electrochromic switching between yellow and deep blue by means of a one-electron redox reaction at its pyrene-based linkers. The rigid MOF stabilizes the radical cations of the pyrene linkers at positive applied potential, resulting in the reversible color change of the MOF film. The regular and uniform channels of the MOF allow ions to migrate through the entire film. The MOF thin film thus exhibits a remarkable color change and rapid switching rate.

A new functionalization technique, solvent-assisted ligand incorporation (SALI), was developed to efficiently incorporate carboxylate-based functionalities in the Zr-based metal-organic framework, NU-1000. Unlike previous metal node functionalization strategies, which utilize dative bonding to coordinatively unsaturated metal sites, SALI introduces functional groups as charge compensating and strongly bound moieties to the Zr6 node. Utilizing SALI, we have efficiently attached perfluoroalkane carboxylates of various chain lengths (C1-C9) on the Zr6 nodes of NU-1000. These fluoroalkane-functionalized mesoporous MOFs, termed herein SALI-n, were studied experimentally and theoretically as potential CO2 capture materials.

A Cu–carborane-based metal–organic framework (MOF), NU-135, which contains a quasi-spherical para-carborane moiety, has been synthesized and characterized. NU-135 exhibits a pore volume of 1.02 cm3/g and a gravimetric BET surface area of ca. 2600 m2/g, and thus represents the first highly porous carborane-based MOF. As a consequence of the unique geometry of the carborane unit, NU-135 has a very high volumetric BET surface area of ca. 1900 m2/cm3. CH4, CO2, and H2 adsorption isotherms were measured over a broad range of pressures and temperatures and are in good agreement with computational predictions. The methane storage capacity of NU-135 at 35 bar and 298 K is ca. 187 vSTP/v. At 298 K, the pressure required to achieve a methane storage density comparable to that of a compressed natural gas (CNG) tank pressurized to 212 bar, which is a typical storage pressure, is only 65 bar. The methane working capacity (5–65 bar) is 170 vSTP/v. The volumetric hydrogen storage capacity at 55 bar and 77 K is 49 g/L. T...

Detachment (desorption) of molecular dyes from photoelectrodes is one of the major limitations for the long-term operation of dye-sensitized solar cells. Here we demonstrate a method to greatly inhibit this loss by growing a transparent metal oxide (TiO2) on the dye-coated photoelectrode via atomic layer deposition (ALD). TiO2-enshrouded sensitizers largely resist detachment, even in pH 10.7 ethanol, a standard solution for intentional removal of molecular dyes from photoelectrodes. Additionally, the ALD post-treatment renders the otherwise hydrophobic dye-coated surface hydrophilic, thereby enhancing photoelectrode pore-filling with aqueous solution.

Methyl-, hydroxymethyl-, and phthalimidomethyl-functionalized versions of the porous organic polymer PAF-1 have been obtained through de novo synthesis. The CO2 adsorption capacity of PAF-1–CH2NH2, obtained through the post-synthesis deprotection of PAF-1–CH2–phthalimide, has been shown to exceed that of PAF-1.

Hydrocarbon-solvent-soluble, isolable, Ziegler-type Ir(0)n nanoparticle hydrogenation catalysts made from the crystallographically characterized [(1,5-COD)Ir(μ-O2C8H15)]2 precatalyst and 2–5 equiv of AlEt3 (≥2 equiv of AlEt3 being required for the best catalysis and stability, vide infra) are scrutinized for their catalytic properties of (1) their isolability and then redispersibility without visible formation of bulk metal; (2) their initial catalytic activity of the isolated nanoparticle catalyst redispersed in cyclohexane; (3) their catalytic lifetime in terms of total turnovers (TTOs) of cyclohexene hydrogenation; and then also and unusually (4) their relative thermal stability in hydrocarbon solution at 200 °C for 30 min. These studies are of interest since Ir(0)n nanoparticles are the currently best-characterized example, and a model/analogue, of industrial Ziegler-type hydrogenation catalysts made, for example, from Co(O2CR)2 and ≥2 equiv of AlEt3. Eight important insights result from the present s...

Nanoparticles supported on high surface area materials are commonly used in many industrially relevant catalytic reactions. This review examines the existing literature of the mechanisms of formation of practical, non-ultra high vacuum, supported-nanoparticle heterogeneous catalysts. Specifically, this review includes: (i) a brief overview of the synthesis of supported-nanoparticles, (ii) an overview of the physical methods for following the kinetics of formation of supported-nanoparticles, and then (iii) a summary of the kinetic and mechanistic studies of the formation of supported nanoparticle catalysts, performed under the traditional synthetic conditions of the gas–solid interface. This review then also discusses (iv) the synthesis, (v) physical methods, and (vi) the extant kinetic and mechanistic studies under the less traditional, less examined conditions of a liquid–solid system. A summary of the main insights from each section of the review is also given. Overall, surprisingly little is known about the mechanism(s) of formation of the desired size, shape and compositionally controlled supported-nanoparticle catalysts.

Reported herein is the synthesis of the previously unknown [Ir(1,5-COD)(μ-H)](4) (where 1,5-COD = 1,5-cyclooctadiene), from commercially available [Ir(1,5-COD)Cl](2) and LiBEt(3)H in the presence of excess 1,5-COD in 78% initial, and 55% recrystallized, yield plus its unequivocal characterization via single-crystal X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, electrospray/atmospheric pressure chemical ionization mass spectrometry (ESI-MS), and UV-vis, IR, and nuclear magnetic resonance (NMR) spectroscopies. The resultant product parallels--but the successful synthesis is different from, vide infra--that of the known and valuable Rh congener precatalyst and synthon, [Rh(1,5-COD)(μ-H)](4). Extensive characterization reveals that a black crystal of [Ir(1,5-COD)(μ-H)](4) is composed of a distorted tetrahedral, D(2d) symmetry Ir(4) core with two long [2.90728(17) and 2.91138(17) Å] and four short Ir-Ir [2.78680 (12)-2.78798(12) Å] bond distances. One 1,5-COD and two edge-bridging hydrides are bound to each Ir atom; the Ir-H-Ir span the shorter Ir-Ir bond distances. XAFS provides excellent agreement with the XRD-obtained Ir(4)-core structure, results which provide both considerable confidence in the XAFS methodology and set the stage for future XAFS in applications employing this Ir(4)H(4) and related tetranuclear clusters. The [Ir(1,5-COD)(μ-H)](4) complex is of interest for at least five reasons, as detailed in the Conclusions section.

Kinetic and mechanistic studies of the formation of supported-nanoparticle catalysts in contact with solution hold promise of driving the next generation syntheses of size, shape, and compositionally controlled catalysts. Recently, we studied the kinetics and mechanism of formation of a prototype Ir(0)∼900/γ-Al2O3 supported-nanoparticle catalyst from Ir(1,5-COD)Cl/γ-Al2O3 in contact with solution (Mondloch, J.E.; Finke, R.G. J. Am. Chem. Soc.2011, 133, 7744). Key kinetic evidence was extracted from γ-Al2O3- and acetone-dependent kinetic curves in the form of rate constants for nucleation (A → B, rate constant k1obs) and autocatalyic surface growth (A + B → 2B, rate constant k2obs), where A is nominally the Ir(1,5-COD)Cl/γ-Al2O3 and B the growing, supported Ir(0)n/γ-Al2O3 nanoparticle. The resultant data provided evidence for a mechanism consisting of four main steps: Ir(1,5-COD)Cl(solvent) dissociation from the γ-Al2O3 support, then Ir(1,5-COD)Cl(solvent) solution-based nucleation, fast nanoparticle captu...

A current goal in heterogeneous catalysis is to transfer the synthetic, as well as developing mechanistic, insights from the modern revolution in nanoparticle science to the synthesis of supported-nanoparticle heterogeneous catalysts. In a recent study (Mondloch, J. E.; Wang, Q.; Frenkel, A. I.; Finke, R. G. J. Am. Chem. Soc. 2010, 132, 9701-9714), we initialized tests of the global hypothesis that quantitative kinetic and mechanistic studies, of supported-nanoparticle heterogeneous catalyst formation in contact with solution, can provide synthetic and mechanistic insights that can eventually drive improved syntheses of composition-, size-, and possibly shape-controlled catalysts. That study relied on the development of a well-characterized Ir(1,5-COD)Cl/γ-Al(2)O(3) precatalyst, which, when in contact with solution and H(2), turns into a nonaggregated Ir(0)(~900)/γ-Al(2)O(3) supported-nanoparticle heterogeneous catalyst. The kinetics of the Ir(1,5-COD)Cl/γ-Al(2)O(3) to Ir(0)(~900)/γ-Al(2)O(3) conversion were followed and fit by a two-step mechanism consisting of nucleation (A → B, rate constant k(1)) followed by autocatalytic surface growth (A + B → 2B, rate constant k(2)). However, a crucial, but previously unanswered question is whether the nucleation and growth steps occur primarily in solution, on the support, or possibly in both phases for one or more of the catalyst-formation steps. The present work investigates this central question for the prototype Ir(1,5-COD)Cl/γ-Al(2)O(3) to Ir(0)(~900)/γ-Al(2)O(3) system. Solvent variation-, γ-Al(2)O(3)-, and acetone-dependent kinetic data, along with UV-vis spectroscopic and gas-liquid-chromatography (GLC) data, are consistent with and strongly supportive of a supported-nanoparticle formation mechanism consisting of Ir(1,5-COD)Cl(solvent) dissociation from the γ-Al(2)O(3) support (i.e., from Ir(1,5-COD)Cl/γ-Al(2)O(3)), solution-based nucleation from that dissociated Ir(1,5-COD)Cl(solvent) species, fast Ir(0)(n) nanoparticle capture by γ-Al(2)O(3), and then subsequent solid-oxide-based nanoparticle growth from Ir(0)(n)/γ-Al(2)O(3) and with Ir(1,5-COD)Cl(solvent), the first kinetically documented mechanism of this type. Those data disprove a solid-oxide-based nucleation and growth pathway involving only Ir(1,5-COD)Cl/γ-Al(2)O(3) and also disprove a solution-based nanoparticle growth pathway involving Ir(1,5-COD)Cl(solvent) and Ir(0)(n) in solution. The present mechanistic studies allow comparisons of the Ir(1,5-COD)Cl/γ-Al(2)O(3) to Ir(0)(~900)/γ-Al(2)O(3) supported-nanoparticle formation system to the kinetically and mechanistically well-studied, Ir(1,5-COD)·P(2)W(15)Nb(3)O(62)(8-) to Ir(0)(~300)·(P(2)W(15)Nb(3)O(62)(8-))(n)(-8n) solution-based, polyoxoanion-stabilized nanoparticle formation and stabilization system. That comparison reveals closely analogous, solution Ir(1,5-COD)(+) or Ir(1,5-COD)Cl-mediated, mechanisms of nanoparticle formation. Overall, the hypothesis supported by this work is that these and analogous studies hold promise of providing a way to transfer the synthetic and mechanistic insights, from the modern revolution in nanoparticle synthesis and characterization in solution, to the rational, mechanism-directed syntheses of solid oxide-supported nanoparticle heterogeneous catalysts, also in contact with solution.

An important question and hence goal in catalysis is how best to transfer the synthetic and mechanistic insights gained from the modern revolution in nanoparticle synthesis, characterization, and catalysis to prepare the next generation of improved, supported-nanoparticle heterogeneous catalysts. It is precisely this question and to-date somewhat elusive goal which are addressed by the present work. More specifically, the global hypothesis investigated herein is that the use of speciation-controlled, well-characterized, solid oxide supported-organometallic precatalysts in contact with solution will lead to the next generation of better composition, size- and shape-controlled, as well as highly active and reproducible, supported-nanoparticle heterogeneous catalysts—ones that can also be understood kinetically and mechanistically. Developed herein are eight criteria defining a prototype system for supported-nanoparticle heterogeneous catalyst formation in contact with solution. The initial prototype system ...

A pressing problem in supported-metal-nanoparticle heterogeneous catalysis—despite the long history and considerable fundamental as well as industrial importance of such heterogeneous catalysts—is how to monitor such catalysts’ formation more routinely, rapidly, and in real time. Such information is needed to better control the size, shape, composition, and thus resultant catalytic activity, selectivity, and lifetime of these important catalysts. To this end, a study is reported of the formation of supported Pt(0)n nanoparticles by H2 reduction of H2PtCl6 on Al2O3 (or TiO2) to give 6 equivalents of HCl plus supported Pt(0)n/Al2O3 (or Pt(0)n/TiO2), all while in contact with a solution of EtOH and cyclohexene. The HCl and Pt(0)n products were confirmed, respectively, by the stoichiometry of HCl formation using pHapparent measurements, appropriate standards, and by TEM and EDX measurements. The hypothesis of this research is that the kinetics of formation of this supported heterogeneous catalyst could be suc...

Thin films of the metal-organic framework (MOF) NU-1000 were grown on conducting glass substrates. The films uniformly cover the conducting glass substrates and are composed of free-standing sub-micrometer rods. Subsequently, atomic layer deposition (ALD) was utilized to deposit Co(2+) ions throughout the entire MOF film via self-limiting surface-mediated reaction chemistry. The Co ions bind at aqua and hydroxo sites lining the channels of NU-1000, resulting in three-dimensional arrays of separated Co ions in the MOF thin film. The Co-modified MOF thin films demonstrate promising electrocatalytic activity for water oxidation.

The nerve agent VX is among the most toxic chemicals known to mankind, and robust solutions are needed to rapidly and selectively deactivate it. Herein, we demonstrate that three Zr6-based metal-organic frameworks (MOFs), namely, UiO-67, UiO-67-NH2, and UiO-67-N(Me)2, are selective and highly active catalysts for the hydrolysis of VX. Utilizing UiO-67, UiO-67-NH2, and UiO-67-N(Me)2 in a pH 10 buffered solution of N-ethylmorpholine, selective hydrolysis of the P-S bond in VX was observed. In addition, UiO-67-N(Me)2 was found to catalyze VX hydrolysis with an initial half-life of 1.8 min. This half-life is nearly 3 orders of magnitude shorter than that of the only other MOF tested to date for hydrolysis of VX and rivals the activity of the best nonenzymatic materials. Hydrolysis utilizing Zr-based MOFs is also selective and facile in the absence of pH 10 buffer (just water) and for the destruction of the toxic byproduct EA-2192.

The availability of efficient hydrogen evolution reaction (HER) catalysts is of high importance for solar fuel technologies aimed at reducing future carbon emissions. Even though Pt electrodes are excellent HER electrocatalysts, commercialization of large-scale hydrogen production technology requires finding an equally efficient, low-cost, earth-abundant alternative. Here, high porosity, metal-organic framework (MOF) films have been used as scaffolds for the deposition of a Ni-S electrocatalyst. Compared with an MOF-free Ni-S, the resulting hybrid materials exhibit significantly enhanced performance for HER from aqueous acid, decreasing the kinetic overpotential by more than 200 mV at a benchmark current density of 10 mA cm−2. Although the initial aim was to improve electrocatalytic activity by greatly boosting the active area of the Ni-S catalyst, the performance enhancements instead were found to arise primarily from the ability of the proton-conductive MOF to favourably modify the immediate chemical environment of the sulfide-based catalyst., Hydrogen evolution technologies for a future carbon-free energy economy require efficient catalysts which can be implemented on a large scale. Here, the authors prepare a composite electrode from readily available elements, whereby a metal-organic framework boosts catalytic performance by enabling rapid proton transport.

A critical review of the emerging field of MOFs for photon collection and subsequent energy transfer is presented. Discussed are examples involving MOFs for (a) light harvesting, using (i) MOF-quantum dots and molecular chromophores, (ii) chromophoric MOFs, and (iii) MOFs with light-harvesting properties, and (b) energy transfer, specifically via the (i) Forster energy transfer and (ii) Dexter exchange mechanism.

The first tritopic carborane-based linker, H3BCA (C15B24O6H30), based on closo-1,10-C2B8H10, has been synthesized and incorporated into a metal–organic framework (MOF), NU-700 (Cu3(BCA)2).

Herein, we describe a strategy for converting catalytically inactive, highly crystalline nanoparticle superlattices embedded in silica into catalytically active, porous structures through superlattice assembly and calcination. First, a body-centered cubic (bcc) superlattice is synthesized through the assembly of two sets of 5 nm gold nanoparticles chemically modified with DNA bearing complementary sticky end sequences. These superlattices are embedded in silica and calcined at 350 °C to provide access to the catalytic nanoparticle surface sites. The calcined superlattice maintains its bcc ordering and has a surface area of 210 m(2)/g. The loading of catalytically active nanoparticles within the superlattice was determined by inductively coupled plasma mass spectrometry, which revealed that the calcined superlattice contained approximately 10% Au by weight. We subsequently investigate the ability of supported Au nanoparticle superlattices to catalyze alcohol oxidation. In addition to demonstrating that calcined superlattices are effective catalysts for alcohol oxidation, electron microscopy reveals preservation of the crystalline structure of the bcc superlattice following calcination and catalysis. Unlike many bulk nanoparticle catalysts, which are difficult to characterize and susceptible to aggregation, nanoparticle superlattices synthesized using DNA interactions offer an attractive bottom-up route to structurally defined heterogeneous catalysts, where one has the potential to independently control nanoparticle size, nanoparticle compositions, and interparticle spacings.

A critical review of the emerging field of MOFs for photon collection and subsequent energy transfer is presented. Discussed are examples involving MOFs for (a) light harvesting, using (i) MOF-quantum dots and molecular chromophores, (ii) chromophoric MOFs, and (iii) MOFs with light-harvesting properties, and (b) energy transfer, specifically via the (i) Forster energy transfer and (ii) Dexter exchange mechanism.

Using the enzymatic mechanism of phosphoesterase as a template, we were able to modify a metal–organic framework such that the hydrolysis rates were 50 times faster than previously demonstrated with UiO-66., The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO2 and UiO-66-(OH)2 showed little to no change in hydrolysis rate. However, UiO-66-NH2 showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe2 and UiO-67-NH2. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH2 is a faster catalyst than UiO-67 and UiO-67-NMe2. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.

Metal–organic frameworks (MOFs) are hybrid porous materials with many potential applications, which intimately depend on the presence of chemical functionality either at the organic linkers and/or at the metal nodes. Functionality that cannot be introduced into MOFs directly via de novo syntheses can be accessed through post-synthesis modification (PSM) on the reactive moieties of the linkers and/or nodes without disrupting the metal–linker bonds. Even more intriguing methods that go beyond PSM are herein termed building block replacement (BBR) which encompasses (i) solvent-assisted linker exchange (SALE), (ii) non-bridging ligand replacement, and (iii) transmetalation. These one-step or tandem BBR processes involve exchanging key structural components of the MOF, which in turn should allow for the evolution of protoMOF structures (i.e., the utilization of a parent MOF as a template) to design MOFs composed of completely new components, presumably via single crystal to single crystal transformations. The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided. Future perspectives providing a glimpse into how these techniques can lead to various unexplored areas of MOF chemistry are also presented.

Metal-organic frameworks (MOFs) built up from Zr6-based nodes and multi-topic carboxylate linkers have attracted attention due to their favourable thermal and chemical stability. However, the hydrolytic stability of some of these Zr6-based MOFs has recently been questioned. Herein we demonstrate that two Zr6-based frameworks, namely UiO-67 and NU-1000, are stable towards linker hydrolysis in H2O, but collapse during activation from H2O. Importantly, this framework collapse can be overcome by utilizing solvent-exchange to solvents exhibiting lower capillary forces such as acetone.

Metal-organic frameworks (MOFs) have gained considerable attention as hybrid materials-in part because of a multitude of potential useful applications, ranging from gas separation to catalysis and light harvesting. Unfortunately, de novo synthesis of MOFs with desirable function-property combinations is not always reliable and may suffer from vagaries such as formation of undesirable topologies, low solubility of precursors, and loss of functionality of the sensitive network components. The recently discovered synthetic approach coined solvent-assisted linker exchange (SALE) constitutes a simple to implement strategy for circumventing these setbacks; its use has already led to the generation of a variety of MOF materials previously unobtainable by direct synthesis methods. This Review provides a perspective of the achievements in MOF research that have been made possible with SALE and examines the studies that have facilitated the understanding and broadened the scope of use of this invaluable synthetic tool.

We designed, synthesized, and characterized a new Zr-based metal-organic framework material, NU-1100, with a pore volume of 1.53 ccg(-1) and Brunauer-Emmett-Teller (BET) surface area of 4020 m(2) g(-1) ; to our knowledge, currently the highest published for Zr-based MOFs. CH4 /CO2 /H2 adsorption isotherms were obtained over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g g(-1) , which corresponds to 43 g L(-1) . The volumetric and gravimetric methane-storage capacities at 65 bar and 298 K are approximately 180 vSTP /v and 0.27 g g(-1) , respectively.

Inspired by biology, in which a bimetallic hydroxide-bridged zinc(II)-containing enzyme is utilized to catalytically hydrolyze phosphate ester bonds, the utility of a zirconium(IV)-cluster-containing metal-organic framework as a catalyst for the methanolysis and hydrolysis of phosphate-based nerve agent simulants was examined. The combination of the strong Lewis-acidic Zr(IV) and bridging hydroxide anions led to ultrafast half-lives for these solvolysis reactions. This is especially remarkable considering that the actual catalyst loading was a mere 0.045 % as a result of the surface-only catalysis observed.

Metal-organic frameworks (MOFs) have gained considerable attention as hybrid materials-in part because of a multitude of potential useful applications, ranging from gas separation to catalysis and light harvesting. Unfortunately, de novo synthesis of MOFs with desirable function-property combinations is not always reliable and may suffer from vagaries such as formation of undesirable topologies, low solubility of precursors, and loss of functionality of the sensitive network components. The recently discovered synthetic approach coined solvent-assisted linker exchange (SALE) constitutes a simple to implement strategy for circumventing these setbacks; its use has already led to the generation of a variety of MOF materials previously unobtainable by direct synthesis methods. This Review provides a perspective of the achievements in MOF research that have been made possible with SALE and examines the studies that have facilitated the understanding and broadened the scope of use of this invaluable synthetic tool.

A boron-rich supramolecular cuboctahedron containing an impressive 240 boron atoms has been synthesized via coordination-driven assembly. The cuboctahedron, which is composed of Cu(2+) paddle-wheel nodes and carborane-isophthalic acids, was obtained simply and in high purity. The ability to precisely characterize the nanostructure via X-ray diffraction makes it unique among boron-rich nanostructures.

Nanoparticles supported on high surface area materials are commonly used in many industrially relevant catalytic reactions. This review examines the existing literature of the mechanisms of formation of practical, non-ultra high vacuum, supported-nanoparticle heterogeneous catalysts. Specifically, this review includes: (i) a brief overview of the synthesis of supported-nanoparticles, (ii) an overview of the physical methods for following the kinetics of formation of supported-nanoparticles, and then (iii) a summary of the kinetic and mechanistic studies of the formation of supported nanoparticle catalysts, performed under the traditional synthetic conditions of the gas–solid interface. This review then also discusses (iv) the synthesis, (v) physical methods, and (vi) the extant kinetic and mechanistic studies under the less traditional, less examined conditions of a liquid–solid system. A summary of the main insights from each section of the review is also given. Overall, surprisingly little is known about the mechanism(s) of formation of the desired size, shape and compositionally controlled supported-nanoparticle catalysts.

An important question and hence goal in catalysis is how best to transfer the synthetic and mechanistic insights gained from the modern revolution in nanoparticle synthesis, characterization, and catalysis to prepare the next generation of improved, supported-nanoparticle heterogeneous catalysts. It is precisely this question and to-date somewhat elusive goal which are addressed by the present work. More specifically, the global hypothesis investigated herein is that the use of speciation-controlled, well-characterized, solid oxide supported-organometallic precatalysts in contact with solution will lead to the next generation of better composition, size- and shape-controlled, as well as highly active and reproducible, supported-nanoparticle heterogeneous catalysts-ones that can also be understood kinetically and mechanistically. Developed herein are eight criteria defining a prototype system for supported-nanoparticle heterogeneous catalyst formation in contact with solution. The initial prototype system explored is the precatalyst, Ir(1,5-COD)Cl/gamma-Al(2)O(3) (characterized via ICP, CO adsorption, IR, and XAFS spectroscopies), and the well-defined product, Ir(0)(n)/gamma-Al(2)O(3) (characterized by reaction stoichiometry, TEM, and XAFS). The Ir(0)(n)/gamma-Al(2)O(3) system proved to be a highly active and long-lived catalyst in the simple test reaction of cyclohexene hydrogenation and in comparison to two literature Ir(0)(n)/Al(2)O(3) heterogeneous catalysts examined under identical conditions. High activity (2.2-4.8-fold higher than that of the literature Ir(0)(n)/Al(2)O(3) catalysts tested under the same conditions) and good lifetime (or = 220,000 total turnovers of cyclohexene hydrogenation) are observed, in part by design since only acetone solvent, cyclohexene, and H(2) are possible ligands in the resultant "weakly ligated/labile-ligand" supported nanoclusters. Significantly, the Ir(1,5-COD)Cl/gamma-Al(2)O(3) + H(2) --Ir(0)(n)/gamma-Al(2)O(3) heterogeneous catalyst formation kinetics were also successfully monitored using the cyclohexene hydrogenation reporter reaction method previously developed and applied to solution-nanoparticle formation. The observed sigmoidal supported-nanoparticle heterogeneous catalyst formation kinetics, starting from the Ir(1,5-COD)Cl/gamma-Al(2)O(3) precatalyst, are closely fit by the two-step mechanism of slow continuous nucleation (A --B, rate constant k(1) = 1.5(1.1) x 10(-3) h(-1)) followed by fast autocatalytic surface growth (A + B --2B, rate constant k(2) = 1.6(2) x 10(4) h(-1) M(-1)), where A is the Ir(1,5-COD)Cl/gamma-Al(2)O(3) precatalyst and B is the resultant Ir(0)(n)/gamma-Al(2)O(3) catalyst. The kinetics are significant in establishing the ability to monitor the formation of supported-nanoparticle heterogeneous catalysts in contact with solution. They also suggest that the nine synthetic and mechanistic insights from the two-step mechanism of nanoparticle formation in solution should now apply also to the formation of supported-nanoparticle heterogeneous catalysts in contact with solution. The results open the door for new syntheses of supported-nanoparticle heterogeneous catalysts under nontraditional, mild, and flexible conditions where supported organometallics and other precursors are in contact with solution, so that additional variables such as the solvent choice, added ligands, solution temperature, and so on can be used to control the catalyst formation steps and, ideally, the resultant supported-nanoparticle heterogeneous catalyst composition, size, and shape.

A pressing problem in supported-metal-nanoparticle heterogeneous catalysis--despite the long history and considerable fundamental as well as industrial importance of such heterogeneous catalysts--is how to monitor such catalysts' formation more routinely, rapidly, and in real time. Such information is needed to better control the size, shape, composition, and thus resultant catalytic activity, selectivity, and lifetime of these important catalysts. To this end, a study is reported of the formation of supported Pt(0)(n) nanoparticles by H(2) reduction of H(2)PtCl(6) on Al(2)O(3) (or TiO(2)) to give 6 equivalents of HCl plus supported Pt(0)(n)/Al(2)O(3) (or Pt(0)(n)/TiO(2)), all while in contact with a solution of EtOH and cyclohexene. The HCl and Pt(0)(n) products were confirmed, respectively, by the stoichiometry of HCl formation using pH(apparent) measurements, appropriate standards, and by TEM and EDX measurements. The hypothesis of this research is that the kinetics of formation of this supported heterogeneous catalyst could be successfully monitored by a fast cyclohexene hydrogenation catalytic reporter reaction method first worked out for monitoring transition-metal nanoparticle formation in solution (Watzky, M. A. and Finke, R. G. J. Am. Chem. Soc. 1997, 119, 10382-10400). Significantly, sigmoidal kinetics of Pt(0)(n)/Al(2)O(3) catalyst formation were in fact successfully monitored by the catalytic hydrogenation reporter reaction method and then found to be well fit to the Finke-Watzky (hereafter F-W) 2-step, slow continuous nucleation and then autocatalytic surface growth mechanism, A --B (rate constant k(1)) and A + B --2B (rate constant k(2)), respectively, in which A is the H(2)PtCl(6) and B is the growing, catalytically active Pt(0) nanoparticle surface. The finding that the F-W mechanism is applicable is significant in that it, in turn, suggests that theor = 8 insights from studies of the mechanisms of soluble nanocluster formation can likely also be applied to supported heterogeneous catalyst synthesis, including a recent equation that gives nanocluster size vs time in terms of k(1), k(2), [A](o) and other parameters (Watzky, M. A., Finney, E. E. and Finke, R. G. J. Am. Chem. Soc. 2008, 130, 11959-11969 ). Also presented are the use of the catalytic reporter reaction to reveal H(2) gas to-solution mass-transfer-limitations (MTL) in the system of H(2)PtCl(6) on TiO(2), results relevant to a recent communication in this journal. The use of the F-W 2-step nucleation and autocatalytic growth kinetic model to fit 3 literature examples of heterogeneous catalyst formation, involving H(2) reduction of both supported or bulk M(x)O(y) (i.e., and in gas-solid reactions), are also presented as part of the Supporting Information. A conclusion section is then provided summarizing the insights and caveats from the present work, as well as some needed future studies.

Platinum complexes have been found to catalyze the transfer of σ-bound ligands to the Ir center in Cp*(PMe3)IrCl2 (Cp* = η5-C5Me5) from Bu3SnPh and PhxSnMe4-x (x = 0−3) complexes. Despite the presence of Sn−Ph bonds in the PhxSnMe4-x complexes, exclusive transfer of the Sn−Me group occurs, an unusual chemoselective process. Examination of the reaction mechanism supports an autocatalytic process.