Impurity doping has been widely used to endow semiconductor nanocrystals with novel optical, electronic, and magnetic functionalities. Here, we introduce a new family of doped NCs offering unique ...insights into the chemical mechanism of doping, as well as into the fundamental interactions between the dopant and the semiconductor host. Specifically, by elucidating the role of relative bond strengths within the precursor and the host lattice, we develop an effective approach for incorporating manganese (Mn) ions into nanocrystals of lead-halide perovskites (CsPbX3, where X = Cl, Br, or I). In a key enabling step not possible in, for example, II–VI nanocrystals, we use gentle chemical means to finely and reversibly tune the nanocrystal band gap over a wide range of energies (1.8–3.1 eV) via postsynthetic anion exchange. We observe a dramatic effect of halide identity on relative intensities of intrinsic band-edge and Mn emission bands, which we ascribe to the influence of the energy difference between the corresponding transitions on the characteristics of energy transfer between the Mn ion and the semiconductor host.
We found that metal−organic framework (MOF) compounds M2(dhtp) (open metal M = Mg, Mn, Co, Ni, Zn; dhtp = 2,5-dihydroxyterephthalate) possess exceptionally large densities of open metal sites. By ...adsorbing one CH4 molecule per open metal, these sites alone can generate very large methane storage capacities, 160−174 cm3(STP)/cm3, approaching the DOE target of 180 cm3(STP)/cm3 for material-based methane storage at room temperature. Our adsorption isotherm measurements at 298 K and 35 bar for the five M2(dhtp) compounds yield excess methane adsorption capacities ranging from 149 to 190 cm3(STP)/cm3 (derived using their crystal densities), indeed roughly equal to the predicted, maximal adsorption capacities of the open metals (within ±10%) in these MOFs. Among the five isostructural MOFs studied, Ni2(dhtp) exhibits the highest methane storage capacity, ∼200 cm3(STP)/cm3 in terms of absolute adsorption, potentially surpassing the DOE target by ∼10%. Our neutron diffraction experiments clearly reveal that the primary CH4 adsorption occurs directly on the open metal sites. Initial first-principles calculations show that the binding energies of CH4 on the open metal sites are significantly higher than those on typical adsorption sites in classical MOFs, consistent with the measured large heats of methane adsorption for these materials. We attribute the enhancement of the binding strength to the unscreened electrostatic interaction between CH4 and the coordinatively unsaturated metal ions.
The development of efficient water oxidation catalysts based on inexpensive and Earth-abundant materials is a prerequisite to enabling water splitting as a feasible source of alternative energy. In ...this work, we report the synthesis of ternary cobalt manganese phosphide nanoparticles from the solution-phase reaction of manganese and cobalt carbonyl complexes with trioctylphosphine. The CoMnP nanoparticles (ca. 5 nm in diameter) are nearly monodisperse and homogeneous in nature. These CoMnP nanoparticles are capable of catalyzing water oxidation at an overpotential of 0.33 V with a 96% Faradaic efficiency when deposited as an ink with carbon black and Nafion. A slight decrease in activity is observed after 500 cycles, which is ascribed to the etching of P into solution, as well as the oxidation of the surface of the nanoparticles. Manganese-based ternary phosphides represent a promising new system to explore for water oxidation catalysis.
The first example of a base metal (manganese) catalyzed acceptorless dehydrogenative coupling of methanol and amines to form formamides is reported herein. The novel pincer complex ...(iPr‐PNHP)Mn(H)(CO)2 catalyzes the reaction under mild conditions in the absence of any additives, bases, or hydrogen acceptors. Mechanistic insight based on the observation of an intermediate and DFT calculations is also provided.
Back to basics: An acceptorless dehydrogenative coupling of methanol and amines to form formamides that is catalyzed by a well‐defined manganese pincer complex (see scheme) is reported. Mechanistic insight based on the observation of an intermediate and density functional calculations is also provided.
In this work, manganese well-dispersed on Fe3O4 microsphere (Mn–Fe3O4) catalyst was synthesized. It exhibited excellent catalytic performance for the direct conversion of carbon dioxide (CO2) into ...light olefins. A CO2 conversion of 44.7% with high selectivity of light olefin (46.2%, yield of 18.7%), high O/P ratio (6.5), and low selectivity of CO (9.4%) was obtained over the 10Mn–Fe3O4 catalyst. The Mn–Fe3O4 catalyst was studied by XRD, SEM, (HR)TEM, STEM–EDS, H2-TPR, and CO2-TPD. The result indicated that the manganese promoter could facilitate the adsorption of CO2 and the activation of CO bonds as well as inhibit the secondary hydrogenation. This work offered a novel Fe-based catalyst system to the utilization of CO2 and an understanding in promoting CO bond activation in the first step of CO2 hydrogenation to hydrocarbon reaction.
A manganese‐catalyzed regio‐ and stereoselective hydroarylation of allenes is reported. The C−H functionalization method provides access to various alkenylated indoles in excellent yields. Moreover, ...a hydroarylation/cyclization cascade involving an unexpected C−N bond cleavage and aryl shift has been developed, which provides a new synthetic approach to substituted pyrroloindolones.
Which way to go: An efficient, scalable, regio‐, and stereoselective manganese‐catalyzed C−H arylation of allenes is reported. When trisubstituted allenes are used, a C−H functionalization/C−N bond cleavage/cyclization cascade affords pyrroloindolones. Mechanistic studies suggest that a manganacycle is formed during the catalytic cycle.
The use of low-cost manganese(II) bromide (MnBr2) and tetramethylethylenediamine (TMEDA) catalyzes the cross coupling of (bis)pinacolatodiboron with a wide range of alkyl halides, demonstrating ...the first manganese-catalyzed coupling with alkyl electrophiles. This method allows access to primary, secondary, and tertiary boronic esters from the parent chlorides, which were previously inaccessible as coupling partners. The reaction proceeds in high yield with as little as 1000 ppm catalyst loading, while 5 mol % can provide high yields in as little as 30 min. Finally, radical-clock experiments revealed that at 0 °C direct borylation outcompetes alternative radical processes, thereby providing synthetically useful, temperature-controlled reaction outcomes.
Cost-effective production of solar fuels requires robust and earth-abundant oxygen evolution reaction (OER) catalysts. Herein, we report that ultrathin nanoplates of cobalt–manganese layered double ...hydroxide (CoMn LDH) are a highly active and stable oxygen evolution catalyst. The catalyst was fabricated by a one-pot coprecipitation method at room temperature, and its turnover frequency (TOF) is more than 20 times higher than the TOFs of Co and Mn oxides and hydroxides, and 9 times higher than the TOF of a precious IrO2 catalyst. The activity of the catalyst was promoted by anodic conditioning, which was proposed to form amorphous regions and reactive Co(IV) species on the surface. The stability of the catalyst was demonstrated by continued electrolysis.
Sodium is globally available, which makes a sodium-ion rechargeable battery preferable to a lithium-ion battery for large-scale storage of electrical energy, provided a host cathode for Na can be ...found that provides the necessary capacity, voltage, and cycle life at the prescribed charge/discharge rate. Low-cost hexacyanometallates are promising cathodes because of their ease of synthesis and rigid open framework that enables fast Na+ insertion and extraction. Here we report an intriguing effect of interstitial H2O on the structure and electrochemical properties of sodium manganese(II) hexacyanoferrates(II) with the nominal composition Na2MnFe(CN)6·zH2O (Na2−δMnHFC). The newly discovered dehydrated Na2−δMnHFC phase exhibits superior electrochemical performance compared to other reported Na-ion cathode materials; it delivers at 3.5 V a reversible capacity of 150 mAh g–1 in a sodium half cell and 140 mAh g–1 in a full cell with a hard-carbon anode. At a charge/discharge rate of 20 C, the half-cell capacity is 120 mAh g–1, and at 0.7 C, the cell exhibits 75% capacity retention after 500 cycles.
Biomass-derived ethanol is an important renewable feedstock. Its conversion into high-quality biofuels is a promising route to replace fossil resources. Herein, an efficient manganese-catalyzed ...Guerbet-type condensation reaction of ethanol to form 1-butanol was explored. This is the first example of upgrading ethanol into higher alcohols using a homogeneous non-noble-metal catalyst. This process proceeded selectively in the presence of a well-defined manganese pincer complex at the parts per million (ppm) level. The developed reaction represents a sustainable synthesis of 1-butanol with excellent turnover number (>110 000) and turnover frequency (>3000 h–1). Moreover, mechanistic studies including control experiments, NMR spectroscopy, and X-ray crystallography identified the essential role of the “N–H moiety” of the manganese catalysts and the major reaction intermediates related to the catalytic cycle.
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