Showing papers in "Inorganic Chemistry in 2015"
TL;DR: A unique three-dimensional Tb-BTB framework with two types of one-dimensional channels was obtained and structurally characterized, exhibiting high thermal stability and Luminescent investigations reveal that 1 can detect Fe(3+) with relatively high sensitivity and selectivity.
Abstract: A unique three-dimensional Tb-BTB framework (1) with two types of one-dimensional channels was obtained and structurally characterized, exhibiting high thermal stability Luminescent investigations reveal that 1 can detect Fe3+ with relatively high sensitivity and selectivity Importantly, 1 as the luminescent probe of Fe3+ can be simply and quickly regenerated, which represents a rare example in reported luminescent sensors of Fe3+
290 citations
TL;DR: The MHT approach has clearly depicted a roadmap for the facile synthesis of zirconium-based water stable MOFs to facilitate their massive production and commercialization.
Abstract: Developing a general and economically viable approach for the large-scale synthesis of water-stable metal–organic frameworks (MOFs) with repeatable quality remains the key step for their massive production and commercialization. We herein report a green (aqueous solutions), mild (100 °C, 1 atm), and scalable (can be up to kilograms) modulated hydrothermal (MHT) synthesis of UiO-66, an iconic MOF that has been widely studied recently for its high water stability. More importantly, the MHT synthetic approach can be applied to synthesize other water-stable MOFs with structures identical to UiO-66, such as UiO-66-(F)4, UiO-66-(OCH2CH3)2, and UiO-66-(COOH)4, which cannot be obtained via the traditional solvothermal method. Their performance in postcombustion CO2 capture has also been evaluated. Our MHT approach has clearly depicted a roadmap for the facile synthesis of zirconium-based water stable MOFs to facilitate their massive production and commercialization.
277 citations
TL;DR: The Mn-incorporated MOF catalyst largely retained its crystallinity throughout prolonged catalysis and was successfully reused over several catalytic runs, exceeding that of the homogeneous reference systems.
Abstract: A manganese bipyridine complex, Mn(bpydc)(CO)3Br (bpydc = 5,5′-dicarboxylate-2,2′-bipyridine), has been incorporated into a highly robust Zr(IV)-based metal–organic framework (MOF) for use as a CO2 reduction photocatalyst. In conjunction with [Ru(dmb)3]2+ (dmb = 4,4′-dimethyl-2,2′-bipyridine) as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificial reductant, Mn-incorporated MOFs efficiently catalyze CO2 reduction to formate in DMF/triethanolamine under visible-light irradiation. The photochemical performance of the Mn-incorporated MOF reached a turnover number of approximately 110 in 18 h, exceeding that of the homogeneous reference systems. The increased activity of the MOF-incorporated Mn catalyst is ascribed to the struts of the framework providing isolated active sites, which stabilize the catalyst and inhibit dimerization of the singly reduced Mn complex. The MOF catalyst largely retained its crystallinity throughout prolonged catalysis and was successfully reused over sever...
270 citations
TL;DR: The pronounced two-dimensionality and the mixture of strong covalent and metallic interactions make MAB-phases to promising candidates for interesting material properties.
Abstract: Single crystals of the ternary borides Cr2AlB2, Cr3AlB4, Cr4AlB6, MoAlB, WAlB, Mn2AlB2, and Fe2AlB2 were grown from the elements with an excess of Al. Structures were refined by X-ray methods on the basis of single crystal data. All compounds crystallize in orthorhombic space groups. In each case boron atoms show the typical trigonal prisms BM6. The BM6-units are linked by common rectangular faces forming B–B-bonds. Thus, zigzag chains of boron atoms are obtained for MoAlB, WAlB, and M2AlB2 (M = Cr, Mn, Fe); chains of hexagons for Cr3AlB4; and double chains of hexagons for Cr4AlB6. The same subunits are known for the binary borides CrB, Cr3B4, Cr2B3, and β-WB, too. The boride partial structures are separated by single layers of Al-atoms in the case of the chromium compounds and double layers for WAlB, i.e., W2Al2B2. All crystal structures can be described using a unified building set principle with quadratic 44-nets of metal atoms. The different compositions and crystal structures are obtained by differen...
258 citations
TL;DR: A promising candidate of a white light emitting X2-type Y2SiO5:Eu(3+),Bi(3+) phosphor, which can be excitable by UV light and address the problems of thermal instability, color aging or re- absorption by commixed phosphors in the coating of the devices.
Abstract: So far, more than 1000 UV converted phosphors have been reported for potential application in white light-emitting diodes (WLEDs), but most of them (e.g., Y2O2S:Eu, YAG:Ce or CaAlSiN3:Eu) suffer from intrinsic problems such as thermal instability, color aging or re-absorption by commixed phosphors in the coating of the devices. In this case, it becomes significant to search a single-phased phosphor, which can efficiently convert UV light to white lights. Herein, we report a promising candidate of a white light emitting X2-type Y2SiO5:Eu3+,Bi3+ phosphor, which can be excitable by UV light and address the problems mentioned above. Single Bi3+-doped X2-type Y2SiO5 exhibits three discernible emission peaks at ∼355, ∼408, and ∼504 nm, respectively, upon UV excitation due to three types of bismuth emission centers, and their relative intensity depends tightly on the incident excitation wavelength. In this regard, proper selection of excitation wavelength can lead to tunable emissions of Y2SiO5:Bi3+ between blue...
241 citations
TL;DR: The results strongly argued that 1 is a real molecular electrocatalyst for water oxidation via a formally Ni(IV) species was proposed and verified.
Abstract: The water-soluble cationic nickel(II) complex of meso-tetrakis(4-N-methylpyridyl)porphyrin (1) can electrocatalyze water oxidation to O2 in neutral aqueous solution (pH 7.0) with the onset of the catalytic wave appearing at ∼1.0 V (vs NHE). The homogeneous catalysis with 1 was verified. Catalyst 1 exhibited water oxidation activity in a pH range 2.0–8.0 and had a strict linear dependence of catalytic current on its concentration. After 10 h of constant potential electrolysis at 1.32 V (vs NHE), a negligible difference of the solution was observed by UV–vis. In addition, inspection of the working electrode by electrochemistry, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX) showed no sign of deposition of NiOx films. These results strongly argued that 1 is a real molecular electrocatalyst for water oxidation. The turnover frequency (TOF) for this process was 0.67 s–1 at 20 °C. On the basis of results from the kinetic isotope effect (KIE) and inhibition experiments, electr...
223 citations
TL;DR: The formation of the "missing linker" defects has been addressed in the model biphenyl-4,4'-dicarboxylate (bpdc)-based Zr MOF, UiO-67, and the dynamic nature of the Zr6 (node)-monocar boxylate bond showed promise in defect functionalization and "healing", including the formation of X-ray-quality "defect-free" Ui O-67 single crystals.
Abstract: For three-dimensional (3D) metal–organic frameworks (MOFs), the presence and nature of structural defects has been recognized as a key factor shaping the material’s physical and chemical behavior. In this work, the formation of the “missing linker” defects has been addressed in the model biphenyl-4,4′-dicarboxylate (bpdc)-based Zr MOF, UiO-67. The defect showed strong dependence on the nature of the modulator acid used in the MOF synthesis; the defects, in turn, were found to correlate with the MOF physical and chemical properties. The dynamic nature of the Zr6 (node)-monocarboxylate bond showed promise in defect functionalization and “healing”, including the formation of X-ray-quality “defect-free” UiO-67 single crystals. Chemical transformations at defect sites have also been explored. The study was also extended to the isoreticular UiO-66 and UiO-68′ systems.
215 citations
TL;DR: The experimental knowledge of the thermal expansion coefficients and precise determination of the cell parameters can potentially also be valuable while conducting density functional theory simulations on these systems in order to deliver more accurate band structure calculations.
Abstract: Lead halogen perovskites, and particularly methylammonium lead iodine, CH3NH3PbI3, have recently attracted considerable interest as alternative solar cell materials, and record solar cell efficiencies have now surpassed 20%. Concerns have, however, been raised about the thermal stability of methylammonium lead iodine, and a phase transformation from a tetragonal to a cubic phase has been reported at elevated temperature. Here, this phase transition has been investigated in detail using temperature-dependent X-ray diffraction measurements. The phase transformation is pinpointed to 54 °C, which is well within the normal operating range of a typical solar cell. The cell parameters were extracted as a function of the temperature, from which the thermal expansion coefficient was calculated. The latter was found to be rather high (αv = 1.57 × 10–4 K–1) for both the tetragonal and cubic phases. This is 6 times higher than the thermal expansion coefficient for soda lime glass and CIGS and 11 times larger than tha...
209 citations
TL;DR: Three types of photocatalytic systems for CO2 reduction, which were recently developed in this group, are reviewed and a novel type of artificial Z-Scheme photocatalyst forCO2 reduction is described, of which photocatalysis is revealed by stepwise excitation of both a semiconductor photoc atalyst unit and the supramolecular photocat catalyst unit.
Abstract: Three types of photocatalytic systems for CO2 reduction, which were recently developed in our group, are reviewed. First, two-component systems containing different rhenium(I) complexes having different roles; i.e., redox photosensitizer and catalyst in the reaction solution are described. The mixed system of a ring-shaped rhenium(I) trinuclear complex and fac-[Re(bpy)(CO)3(MeCN)]+ is currently the most efficient photocatalytic system for CO2 reduction (ΦCO = 0.82 at λex = 436 nm). The second is a series of supramolecular photocatalysts, which have units with different functions in one molecule, i.e., redox photosensitizer, catalyst, and bridging ligand. The highest durability and speed of photocatalysis were achieved by using this system (ΦCO = 0.45, TONCO = 3029, and TOFCO = 35.7 min–1). The third is a novel type of artificial Z-Scheme photocatalyst for CO2 reduction, of which photocatalysis is revealed by stepwise excitation of both a semiconductor photocatalyst unit and the supramolecular photocatalys...
194 citations
TL;DR: This paper describes the recent progress in catalytic nitrogen fixation by using transition-metal-dinitrogen complexes as catalysts and may provide new access to the development of economical nitrogen fixation in place of the Haber-Bosch process.
Abstract: This paper describes our recent progress in catalytic nitrogen fixation by using transition-metal–dinitrogen complexes as catalysts. Two reaction systems for the catalytic transformation of molecular dinitrogen into ammonia and its equivalent such as silylamine under ambient reaction conditions have been achieved by the molybdenum–, iron–, and cobalt–dinitrogen complexes as catalysts. Many new findings presented here may provide new access to the development of economical nitrogen fixation in place of the Haber–Bosch process.
192 citations
TL;DR: It is unambiguously demonstrated, solely on the basis of experimental data, that Orbach relaxation cannot a priori be considered as the main mechanism determining the spin dynamics of SMMs and consideration of additional design criteria that address the presence of alternative relaxation processes beyond the traditional double-well picture is required.
Abstract: Determination of the electronic energy spectrum of a trigonalsymmetry mononuclear Yb3+ single-molecule magnet (SMM) by highresolution
absorption and luminescence spectroscopies reveals that the first excited electronic doublet is placed nearly 500 cm−1 above the ground one.
Fitting of the paramagnetic relaxation times of this SMM to a thermally activated (Orbach) model {τ = τ0 × exp[ΔOrbach/(kBT)]} affords an activation
barrier, ΔOrbach, of only 38 cm−1. This result is incompatible with the spectroscopic observations. Thus, we unambiguously demonstrate, solely on
the basis of experimental data, that Orbach relaxation cannot a priori be considered as the main mechanism determining the spin dynamics of SMMs.
This study highlights the fact that the general synthetic approach of optimizing SMM behavior by maximization of the anisotropy barrier, intimately linked to
the ligand field, as the sole parameter to be tuned, is insufficient because of the complete neglect of the interaction of the magnetic moment of the molecule with its environment. The Orbach mechanism is expected dominant only in the cases in which the energy of the excited ligand
field state is below the Debye temperature, which is typically low for molecular crystals and, thus, prevents the use of the
anisotropy barrier as a design criterion for the realization of high-temperature SMMs. Therefore, consideration of additional
design criteria that address the presence of alternative relaxation processes beyond the traditional double-well picture is required.
TL;DR: It is shown that large energy barriers to magnetic relaxation, Ueff, can be achieved in the absence of near-linearity and generally that any two-coordinate complex of Dy(III) is an attractive synthetic target that may possess Ueff > 1000 cm(-1).
Abstract: Design criteria to obtain slow magnetic relaxation are theoretically investigated for two-coordinate complexes of DyIII. It is shown that large energy barriers to magnetic relaxation, Ueff, can be achieved in the absence of near-linearity and generally that any two-coordinate complex of DyIII is an attractive synthetic target that may possess Ueff > 1000 cm–1. These large Ueff values are immediately diminished if axial ligation is disrupted by solvent coordination.
TL;DR: TMU-6 had a lower adsorption efficiency for metal ions than the other two MOFs, and TMU-5 was chosen as an efficient sorbent for the extraction and preconcentration of trace amounts of some heavy-metal ions followed by their determination by flow injection inductively coupled plasma optical emission spectrometry.
Abstract: The three zinc(II) metal-organic frameworks [Zn2(oba)2(4-bpdb)]·(DMF)x (TMU-4), [Zn(oba)(4-bpdh)0.5]n·(DMF)y (TMU-5), and [Zn(oba)(4-bpmb)0.5]n·(DMF)z (TMU-6) [DMF = dimethylformamide, H2oba = 4,4'-oxybisbenzoic acid, 4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene, and 4-bpmb = N(1),N(4)-bis((pyridin-4-yl)methylene)benzene-1,4-diamine], which contain azine-functionalized pores, have been successfully synthesized by mechanosynthesis as a convenient, rapid, low-cost, solventless, and green process. These MOFs were studied for the removal and extraction of some heavy-metal ions from aqueous samples, and the effects of the basicity and void space of these MOFs on adsorption efficiency were evaluated. The results showed that, for trace amounts of metal ions, the basicity of the N-donor ligands in the MOFs determines the adsorption efficiency of the MOFs for the metal ions. In contrast, at high concentrations of metal ions, the void space of the MOFs plays a main role in the adsorption process. The studies conducted revealed that, among the three MOFs, TMU-6 had a lower adsorption efficiency for metal ions than the other two MOFs. This result can be attributed to the greater basicity of the azine groups on the TMU-4 and TMU-5 pore walls as compared to the imine groups on the N-donor ligands on the TMU-6 pore walls. Subsequently, TMU-5 was chosen as an efficient sorbent for the extraction and preconcentration of trace amounts of some heavy-metal ions including Cd(II), Co(II), Cr(III), Cu(II), and Pb(II), followed by their determination by flow injection inductively coupled plasma optical emission spectrometry. Several variables affecting the extraction efficiency of the analytes were investigated and optimized. The optimized methodology exhibits a good linearity between 0.05 and 100 μg L(-1) (R(2) > 0.9935) and detection limits in the range of 0.01-1.0 μg L(-1). The method has enhancement factors between 42 and 225 and relative standard deviations (RSDs) of 2.9-6.2%. Subsequently, the potential applicability of the proposed method was evaluated for the extraction and determination of target metal ions in some environmental water samples.
TL;DR: A stable porous carbazole-based luminescent metal-organic framework, NENU-522, was successfully constructed, which provides the strategy for luminecent material encapsulation of Ln(3+) ions with tunable luminescence for application in light emission.
Abstract: A stable porous carbazole-based luminescent metal-organic framework, NENU-522, was successfully constructed. It is extremely stable in air and acidic/basic aqueous solutions, which provides the strategy for luminescent material encapsulation of Ln(3+) ions with tunable luminescence for application in light emission. More importantly, Ln(3+)@NENU-522 can emit white light by encapsulating different molar ratios of Eu(3+) and Tb(3+) ions. Additionally, Tb(3+)@NENU-522 is found to be useful as a fluorescent indicator for the qualitative and quantitative detection of nitroaromatic explosives with different numbers of -NO2 groups, and the concentrations of complete quenching are about 2000, 1000, and 80 ppm for nitrobenzene, 1,3-dinitrobenzene, and 2,4,6-trinitrophenol, respectively. Meanwhile, Tb(3+)@NENU-522 displays high selectivity and recyclability in the detection of nitroaromatic explosives.
TL;DR: Two amino-decorated metal-organic frameworks have been constructed, which are the rare examples of MOF-based fluorescent probes targeting environmentally relevant guest species in aqueous solution, with high selectivity and sensitivity.
Abstract: Two amino-decorated metal–organic frameworks have been constructed, which are the rare examples of MOF-based fluorescent probes targeting environmentally relevant guest species, such as Hg (II) and Cr (VI) ions in aqueous solution, with high selectivity and sensitivity. The possible sensing mechanism is also discussed.
TL;DR: It is proved that the β-diketonate coligands can play an important role in modulating magnetic dynamics of the lanthanide 8-hydroxyquinoline Schiff base derivative system.
Abstract: New dinuclear lanthanide(III) complexes based on an 8-hydroxyquinoline Schiff base derivative and β-diketonate ligands, [Ln2(hfac)4(L)2] (Ln(III) = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)), [Ln2(tfac)4(L)2] (Ln(III) = Gd (6), Tb (7), Dy (8), Ho (9)), and [Dy(bfac)4(L)2·C7H16] (10) (L = 2-[[(4-fluorophenyl)imino] methyl]-8-hydroxyquinoline, hfac = hexafluoroacetylacetonate, tfac = trifluoroacetylacetonate, and bfac = benzoyltrifluoroacetone), have been synthesized. The single-crystal X-ray diffraction data show that complexes 1-10 are phenoxo-O-bridged dinuclear complexes; each eight-coordinated center Ln(III) ion is in a slightly distorted dodecahedral geometry with two bidentate β-diketonate coligands and two μ2-O bridging 8-hydroxyquinoline Schiff base derivative ligands. The magnetic study reveals that 1 and 6 display cryogenic magnetic refrigeration properties, whereas complexes 3, 8, and 10 show different SMM behaviors with energy barriers of 6.77 K for 3, 19.83 K for 8, and 25.65 K for 10. Meanwhile, slow magnetic relaxation was observed in 7, while no out-of-phase alternating-current signals were found for 2. The different dynamic magnetic behaviors of two Tb2 complexes and the three Dy2 complexes mainly derive from the tiny crystal structure changes around the Ln(III) ions. It is also proved that the β-diketonate coligands can play an important role in modulating magnetic dynamics of the lanthanide 8-hydroxyquinoline Schiff base derivative system.
TL;DR: This study provides a facile method to develop solid-solution-like MOFs for heterogeneous catalysis and highlights the great potential of this mixed-metal strategy in the development of MOFs with specific endowed functionalities.
Abstract: Different amounts of Co-substituted Ni-MOF-74 have been prepared via a post-synthetic metal exchange Inductively coupled plasma mass spectrometry, powder X-ray diffraction (XRD), N2 adsorption/desorption, and extended X-ray absorption fine structure (EXAFS) analyses indicated the successful metathesis between Co and Ni in Ni-MOF-74 to form the solid-solution-like mixed-metal Co/Ni-MOF-74 It was found that introduction of active Co into the Ni-MOF-74 framework enabled the inert Ni-MOF-74 to show activity for cyclohexene oxidation Since Co was favorably substituted at positions more accessible to the substrate, the mixed-metal Co/Ni-MOF-74 showed superior catalytic performance, compared with pure Co-MOF-74 containing a similar amount of Co This study provides a facile method to develop solid-solution-like MOFs for heterogeneous catalysis and highlights the great potential of this mixed-metal strategy in the development of MOFs with specific endowed functionalities
TL;DR: The first estimates of the standard reduction potential of the O2 + 4e(-) + 4H(+) ⇋ 2H2O couple in organic solvents are reported, and extensions to other reduction potentials are discussed.
Abstract: A variety of next-generation energy processes utilize the electrochemical interconversions of dioxygen and water as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Reported here are the first estimates of the standard reduction potential of the O2 + 4e– + 4H+ ⇋ 2H2O couple in organic solvents. The values are +1.21 V in acetonitrile (MeCN) and +0.60 V in N,N-dimethylformamide (DMF), each versus the ferrocenium/ferrocene couple (Fc+/0) in the respective solvent (as are all of the potentials reported here). The potentials have been determined using a thermochemical cycle that combines the free energy for transferring water from aqueous solution to organic solvent, −0.43 kcal mol–1 for MeCN and −1.47 kcal mol–1 for DMF, and the potential of the H+/H2 couple, – 0.028 V in MeCN and −0.662 V in DMF. The H+/H2 couple in DMF has been directly measured electrochemically using the previously reported procedure for the MeCN value. The thermochemical approach used for the O2/H2O couple has...
TL;DR: If focused on the requirements of a short TadF decay time for reduction of the saturation effects in OLEDs, copper(I) complexes are well comparable or even slightly better than the best purely organic TADF emitters.
Abstract: A comparison of three copper(I) compounds [1, Cu(dppb)(pz2Bph2); 2, Cu(pop)(pz2Bph2); 3, Cu(dmp)(phanephos)+] that show pronounced thermally activated delayed fluorescence (TADF) at ambient temperature demonstrates a wide diversity of emission behavior. In this study, we focus on compound 1. A computational density functional theory (DFT)/time-dependent DFT approach allows us to predict detailed photophysical properties, while experimental emission studies over a wide temperature range down to T = 1.5 K lead to better insight into the electronic structures even with respect to spin–orbit coupling efficiencies, radiative rates, and zero-field splitting of the triplet state. All three compounds, with emission quantum yields higher than ϕPL = 70%, are potentially well suited as emitters for organic light-emitting diodes (OLEDs) based on the singlet-harvesting mechanism. Interestingly, compound 1 is by far the most attractive one because of a very small energy separation between the lowest excited singlet S1 ...
TL;DR: A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature.
Abstract: A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature. The sensing mechanism in the europium-doped compound Tb0.95Eu0.05HL (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) is based not only on phonon-assisted energy transfer from Tb(III) to Eu(III) centers, but also on phonon-assisted energy migration between neighboring Tb(III) ions. It shows good performance in a wide temperature range, especially in the range 4-50 K, reaching a sensitivity up to 31% K(-1) at 4 K.
TL;DR: Interestingly, the luminescence turn-on-based selectivity of Al(3+) ions in aqueous medium was achieved even in the presence of the highest quenchable metal ion, Fe(3+).
Abstract: A new metal–organic framework [Co(OBA)(DATZ)0.5(H2O)] {OBA = 4,4′-oxybis(benzoic acid) and DATZ = 3,5-diamino-1,2,4-triazole}, 1, was synthesized by hydrothermal reaction. Single-crystal X-ray data of 1 confirmed two-dimensional rhombus grid network topology with a free nitrogen site of triazole ring and two amine groups of each DATZ. Photoluminescence study of 1 in aqueous medium shows blue emission at 407 nm upon excitation at 283 nm. This emissive property was used for the sensing of Al3+ ions in aqueous medium through very high luminescence turn-on (6.3-fold) along with the blue shifting (∼24 nm) of the emission peak. However, luminescence studies in the presence of other common metal ions such as Mg2+, Zn2+, Ni2+, Co2+, Mn2+, K+, Na+, Ca2+, Cd2+, Hg2+, Cu2+, Fe2+, Fe3+, and Cr3+ in aqueous medium shows luminescence quenching in varying extent. Interestingly, the luminescence turn-on-based selectivity of Al3+ ions in aqueous medium was achieved even in the presence of the highest quenchable metal ion,...
TL;DR: It is shown that, with appropriate attention to ligand/node stoichiometry, SALI can also be achieved with phosphonate-terminated ligands, and this change extends the pH range for retention of incorporated ligands.
Abstract: Solvent-assisted ligand incorporation (SALI) is useful for functionalizing the channels of metal–organic framework (MOF) materials such as NU-1000 that offer substitutionally labile zirconium(IV) coordination sites for nonbridging ligands. Each of the 30 or so previous examples relied upon coordination of a carboxylate ligand to achieve incorporation. Here we show that, with appropriate attention to ligand/node stoichiometry, SALI can also be achieved with phosphonate-terminated ligands. Consistent with stronger M(IV) coordination of phosphonates versus carboxylates, this change extends the pH range for retention of incorporated ligands. The difference in coordination strength can be exploited to achieve stepwise incorporation of pairs of ligands—specifically, phosphonates species followed by carboxylate species—without danger of displacement of the first ligand type by the second. Diffuse reflectance infrared Fourier-transform spectroscopy suggests that the phosphonate ligands are connected to the MOF no...
TL;DR: Experimental work, including voltammetry and product quantification from controlled potential electrolysis, suggests a key mechanistic role for the phenolic proton in the conversion of CO2 to CO.
Abstract: The design, synthesis, and assessment of a new manganese-centered catalyst for the electrochemical reduction of CO2 is described. The reported species, MnBr(6-(2-hydroxyphenol)-2,2′-bipyridine)(CO)3, includes a ligand framework with a phenolic proton in close proximity to the CO2 binding site, which allows for facile proton-assisted C–O bond cleavage. As a result of this modification, seven times the electrocatalytic current enhancement is observed compared to MnBr(2,2′-bipyridine)(CO)3. Moreover, reduction is possible at only 440 mV of overpotential. Theoretical computations suggest that the entropic contribution to the activation free energy is partially responsible for the increased catalytic activity. Experimental work, including voltammetry and product quantification from controlled potential electrolysis, suggests a key mechanistic role for the phenolic proton in the conversion of CO2 to CO.
TL;DR: Evaluation of UiO-66 and UIO-67 metal-organic framework derivatives as catalysts for the degradation of soman showed the importance of both the linker size and functionality.
Abstract: Evaluation of UiO-66 and UiO-67 metal–organic framework derivatives as catalysts for the degradation of soman, a chemical warfare agent, showed the importance of both the linker size and functionality. The best catalysts yielded half-lives of less than 1 min. Further testing with a nerve agent simulant established that different rate-assessment techniques yield similar values for degradation half-lives.
TL;DR: The X-ray diffraction and structure refinement, diffuse reflection, photoluminescence (PL), and fluorescent decay curves were used to characterize the as-prepared samples and indicate the promising application in UV-pumped white-emitting lighting diodes field.
Abstract: A series of Ln(3+) (Ln(3+) = Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+)) ion doped CaNb2O6 (CNO) phosphors have been prepared via the conventional high-temperature solid-state reaction route. The X-ray diffraction (XRD) and structure refinement, diffuse reflection, photoluminescence (PL), and fluorescent decay curves were used to characterize the as-prepared samples. Under UV radiation, the CNO host present a broad emission band from about 355 to 605 nm centered around 460 nm originating from the NbO6 octahedral groups, which has spectral overlaps with the excitation of f-f transitions of Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) in CNO:Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) samples. They show both host emission and respective emission lines derived from the characteristic f-f transitions of activators, which present different emission colors owing to the energy transfer from the NbO6 group in the host to Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) with increasing activator concentrations. The decreases of decay lifetimes of host emissions in CNO:Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) demonstrate the energy transfer from the hosts to Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+). The energy transfer mechanisms in CNO:Eu(3+)/Tb(3+)/Dy(3+) phosphors have been determined to be a resonant type via dipole-dipole mechanisms. For CNO:Sm(3+), the metal-metal charge transfer transition (MMCT) might contribute to the different variations of decay lifetimes and emission intensity from CNO:Eu(3+)/Tb(3+)/Dy(3+) samples. The best quantum efficiency is 71.2% for CNO:0.01/0.02Dy(3+). The PL properties of as-prepared materials indicate the promising application in UV-pumped white-emitting lighting diodes field.
TL;DR: The results highlight the unique potential of metal-organic frameworks as a class of heterogeneous catalysts that allow unparalleled structural characterization and control over their active sites.
Abstract: Metal–organic frameworks featuring ligands with open chelating groups are versatile platforms for the preparation of a diverse set of heterogeneous catalysts through postsynthetic metalation. The crystalline nature of these materials allows them to be characterized via X-ray diffraction, which provides valuable insight into the structure of the metal sites that facilitate catalysis. A highly porous and thermally robust zirconium-based metal–organic framework, Zr6O4(OH)4(bpydc)6 (bpydc2– = 2,2′-bipyridne-5,5′-dicarboxylate), bears open bipyridine sites that readily react with a variety of solution- and gas-phase metal sources to form the corresponding metalated frameworks. Remarkably, Zr6O4(OH)4(bpydc)6 undergoes a single-crystal-to-single-crystal transformation upon metalation that involves a change in space group from Fm3m to Pa3. This structural transformation leads to an ordering of the metalated linkers within the framework, allowing structural characterization of the resulting metal complexes. Furt...
TL;DR: A novel cadmium-based metal-organic framework (MOF) material with dual-emission signals has been constructed that can act as the first example of MOF-implicated ratiometric sensor for mercury(II) in pure water with a fast response, high selectivity, and sensitivity.
Abstract: A novel cadmium-based metal–organic framework (MOF) material with dual-emission signals has been constructed that can act as the first example of MOF-implicated ratiometric sensor for mercury(II) in pure water with a fast response, high selectivity, and sensitivity. The sensing mechanism is also discussed.
TL;DR: A facile and general approach for the fabrication of highly dispersed Au, Pd, and Pt nanoparticles (NPs) on MIL-125(Ti) without using extra reducing and capping agents is demonstrated.
Abstract: We demonstrate a facile and general approach for the fabrication of highly dispersed Au, Pd, and Pt nanoparticles (NPs) on MIL-125(Ti) without using extra reducing and capping agents. Noble-metal NP formation is directed by an in situ redox reaction between the reductive MIL-125(Ti) with Ti3+ and oxidative metal salt precursors. The resulting composites function as efficient photocatalysts.
TL;DR: In this paper, a combined theoretical and experimental study is performed in order to elucidate the effects of linker functional groups on the photoabsorption properties of UiO-66-X materials.
Abstract: A combined theoretical and experimental study is performed in order to elucidate the effects of linker functional groups on the photoabsorption properties of UiO-66-X materials. This study, in which both mono- and difunctionalized linkers (with X = OH, NH2, or SH) are investigated, aims to obtain a more complete picture of the choice of functionalization. Static time-dependent density functional theory calculations combined with molecular dynamics simulations are performed on the linkers, and the results are compared to experimental UV/vis spectra in order to understand the electronic effects governing the absorption spectra. The disubstituted linkers show larger shifts than the monosubstituted variants, making them promising candidates for further study as photocatalysts. Next, the interaction between the linker and the inorganic part of the framework is theoretically investigated using a cluster model. The proposed ligand-to-metal-charge transfer is theoretically observed and is influenced by the differ...
TL;DR: Porous Co3O4 hollow tetrahedra were prepared through the thermolysis of metal-organic frameworks and presented reversible capacities of 1196 and 1052 mAh g(-1) at 50 and 200 mA g (-1) after 60 charge/discharge cycles, respectively.
Abstract: Porous Co3O4 hollow tetrahedra were prepared through the thermolysis of metal-organic frameworks and presented reversible capacities of 1196 and 1052 mAh g(-1) at 50 and 200 mA g(-1) after 60 charge/discharge cycles, respectively. Such excellent performances stem from the well-defined hollow structure of Co3O4 tetrahedra.