Search

Here, doubly protonated Lindqvist‐type niobium oxide cluster [H2(Nb6O19)]6–, fabricated by microwave‐assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C−H bond with pKa >26 and proton abstraction from a base indicator with pKa=26.5. Surprisingly, [H2(Nb6O19)]6− exhibited water‐tolerant superbase properties for Knoevenagel and crossed aldol condensation reactions in the presence of water, although it is well known that the strong basicity of metal oxides and organic superbase is typically lost by the adsorption of water. Density functional theory calculation revealed that the basic surface oxygens that share the corner of NbO6 units in [H2(Nb6O19)]8− maintained the negative charges even after proton adsorption. This proton capacity and the presence of un‐protonated basic sites led to the water tolerance of the superbase catalysis. [ABSTRACT FROM AUTHOR]

The thermal behaviors of ligand-protected metal clusters, [Au9(PPh3)8]3+ and [MAu8(PPh3)8]2+ (M = Pd, Pt) with a crown-motif structure, were investigated to determine the effects of the gas composition, single-atom doping, and counter anions on the thermal stability of these clusters. We successfully synthesized crown-motif [PdAu8(PPh3)8][HPMo12O40] (PdAu8–PMo12) and [PtAu8(PPh3)8][HPMo12O40] (PtAu8–PMo12) salts with a cesium-chloride-type structure, which is the same as the [Au9(PPh3)8][PMo12O40] (Au9–PMo12) structure. Thermogravimetry-differential thermal analysis/mass spectrometry analysis revealed that the crown-motif structure of Au9–PMo12 was decomposed at ∼475 K without weight loss to form Au nanoparticles. After structural decomposition, the ligands were desorbed from the sample. The ligand desorption temperature of Au9–PMo12 increased under 20% O2 conditions because of the formation of Au nanoparticles and stronger interaction of the formed O=PPh3 than PPh3. The Pd and Pt single-atom doping improved the thermal stability of the clusters. This improvement was due to the formation of a large bonding index of M–Au and a change in Au–PPh3 bonding energy by heteroatom doping. Moreover, we found that the ligand desorption temperatures were also affected by the type of counter anions, whose charge and size influence the localized Coulomb interaction and cluster packing between the cationic ligand-protected metal clusters and counter anions. [ABSTRACT FROM AUTHOR]

Controlling the geometric structures of metal clusters through structural isomerization allows for tuning of their electronic state. In this study, we successfully synthesized butterfly-motif [PdAu8(PPh3)8]2+ (PdAu8-B, B means butterfly-motif) and [PtAu8(PPh3)8]2+ (PtAu8-B) by the structural isomerization from crown-motif [PdAu8(PPh3)8]2+ (PdAu8-C, C means crown-motif) and [PtAu8(PPh3)8]2+ (PtAu8-C), induced by association with anionic polyoxometalate, [Mo6O19]2– (Mo6) respectively, whereas their structural isomerization was suppressed by the use of [NO3]– and [PMo12O40]3– as counter anions. DR-UV-vis-NIR and XAFS analyses and density functional theory calculations revealed that the synthesized [PdAu8(PPh3)8][Mo6O19] (PdAu8-Mo6) and [PtAu8(PPh3)8][Mo6O19] (PtAu8-Mo6) had PdAu8-B and PtAu8-B respectively because PdAu8-Mo6 and PtAu8-Mo6 had bands in optical absorption at the longer wavelength region and different structural parameters characteristic of the butterfly-motif structure obtained by XAFS analysis. Single-crystal and powder X-ray diffraction analyses revealed that PdAu8-B and PtAu8-B were surrounded by six Mo6 with rock salt-type packing, which stabilizes the semi-stable butterfly-motif structure to overcome high activation energy for structural isomerization. Controlling the geometric structures of metal clusters through structural isomerization allows for tuning of their optical and catalytic properties. Here, structural isomerization of crown-motif clusters [PdAu8(PPh3)8]2+ and [PtAu8(PPh3)8]2+ to corresponding butterfly-motif clusters is induced using [Mo6O19]2- anions. [ABSTRACT FROM AUTHOR]

Keywords: catalysts; metal clusters; nanostructures; photocatalysts; water splitting EN catalysts metal clusters nanostructures photocatalysts water splitting 21074 21074 1 09/16/21 20210920 NES 210920 B A ligand-desorption process b during calcination was followed for metal-oxide-supported 2-phenylethanethiolate-protected gold 25-atom metal nanoclusters (NCs) using five experimental techniques by Yuichi Negishi and co-workers in their Research Article on page 21340. Inside Cover: Creation of High-Performance Heterogeneous Photocatalysts by Controlling Ligand Desorption and Particle Size of Gold Nanocluster (Angew. Based on the obtained knowledge, a method to form a metal-oxide layer on the surface of Au NCs while preventing their aggregation was established, and thereby a water-splitting photocatalyst with high activity and stability was created. [Extracted from the article]

Innentitelbild: Creation of High-Performance Heterogeneous Photocatalysts by Controlling Ligand Desorption and Particle Size of Gold Nanocluster (Angew. Keywords: catalysts; metal clusters; nanostructures; photocatalysts; water splitting EN catalysts metal clusters nanostructures photocatalysts water splitting 21242 21242 1 09/16/21 20210920 NES 210920 B Die Ligandendesorption b bei der Kalzinierung von Metalloxid-gestützten 2-Phenylethanthiolat-geschützten 25-atomigen Gold-Nanoclustern wurde von Yuichi Negishi und Mitarbeitern im Forschungsartikel auf S. 21510 mit fünf experimentellen Techniken untersucht. Catalysts, metal clusters, nanostructures, photocatalysts, water splitting. [Extracted from the article]

The solid base catalysis of sodium salts of Lindqvist-type metal oxide clusters was investigated using a Knoevenagel condensation reaction. We successfully synthesized the sodium salts of Ta and Nb mixed-oxide clusters Na8−nHn[(Ta6−xNbx)O19]·15H2O (Na-Ta6−xNbx, n = 0, 1, x = 0–6) and found them to exhibit activity for proton abstraction from nitrile substrates with a pKa value of 23.8, which is comparable to that of the conventional solid base MgO. The Ta-rich Na-Ta6 and Na-Ta4Nb2 exhibited high activity among Ta and Nb mixed-oxide clusters. Synchrotron X-ray diffraction (SXRD) measurements, Fourier-transform infrared (FT-IR) spectroscopy, and X-ray absorption spectroscopy (XAS) revealed the structure of Na-Ta6−xNbx: (1) The crystal structure changed from Na7H[M6O19]·15H2O to Na8[M6O19]·15H2O (M = Ta or Nb) by the anisotropic expansion of the unit cell with an increase in Ta content; (2) Highly symmetrical Lindqvist [Ta6−xNbxO19]8− was generated in Na-Ta4Nb2 and Na-Ta6 because of the symmetrical association of Na+ ions with [Ta6−xNbxO19]8− in the structure. DFT calculation revealed that the Lindqvist structures with high symmetry have large NBO charges on surface oxygen species, which are strongly related to base catalytic activity, whereas the composition hardly affects the NBO charges. The above results showed that the Brønsted base catalysis was sensitive to the symmetry of the Lindqvist [Ta6−xNbxO19]8− structure. These findings contribute to the design of solid base catalysts composed of anionic metal oxide clusters with alkaline-metal cations. [ABSTRACT FROM AUTHOR]

Here, doubly protonated Lindqvist-type niobium oxide cluster [H 2 (Nb 6 O 19 )] 6- , fabricated by microwave-assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C-H bond with pK a >26 and proton abstraction from a base indicator with pK a =26.5. Surprisingly, [H 2 (Nb 6 O 19 )] 6- exhibited water-tolerant superbase properties for Knoevenagel and crossed aldol condensation reactions in the presence of water, although it is well known that the strong basicity of metal oxides and organic superbase is typically lost by the adsorption of water. Density functional theory calculation revealed that the basic surface oxygens that share the corner of NbO 6 units in [H 2 (Nb 6 O 19 )] 8- maintained the negative charges even after proton adsorption. This proton capacity and the presence of un-protonated basic sites led to the water tolerance of the superbase catalysis., (© 2024 Wiley‐VCH GmbH.)

The phase separation between a liquid amine and the solid carbamic acid exhibited >99% CO 2 removal efficiency under a 400 ppm CO 2 flow system using diamines bearing an aminocyclohexyl group. Among them, isophorone diamine [IPDA; 3-(aminomethyl)-3,5,5-trimethylcyclohexylamine] exhibited the highest CO 2 removal efficiency. IPDA reacted with CO 2 in a CO 2 /IPDA molar ratio of ≥1 even in H 2 O as a solvent. The captured CO 2 was completely desorbed at 333 K because the dissolved carbamate ion releases CO 2 at low temperatures. The reusability of IPDA under CO 2 adsorption-and-desorption cycles without degradation, the >99% efficiency kept for 100 h under direct air capture conditions, and the high CO 2 capture rate (201 mmol/h for 1 mol of amine) suggest that the phase separation system using IPDA is robust and durable for practical use., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Recently, the creation of new heterogeneous catalysts using the unique electronic/geometric structures of small metal nanoclusters (NCs) has received considerable attention. However, to achieve this, it is extremely important to establish methods to remove the ligands from ligand-protected metal NCs while preventing the aggregation of metal NCs. In this study, the ligand-desorption process during calcination was followed for metal-oxide-supported 2-phenylethanethiolate-protected gold (Au) 25-atom metal NCs using five experimental techniques. The results clearly demonstrate that the ligand-desorption process consists of ligand dissociation on the surface of the metal NCs, adsorption of the generated compounds on the support and desorption of the compounds from the support, and the temperatures at which these processes occurred were elucidated. Based on the obtained knowledge, we established a method to form a metal-oxide layer on the surface of Au NCs while preventing their aggregation, thereby succeeding in creating a water-splitting photocatalyst with high activity and stability., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The thermal behaviors of ligand-protected metal clusters, [Au 9 (PPh 3 ) 8 ] 3+ and [MAu 8 (PPh 3 ) 8 ] 2+ (M = Pd, Pt) with a crown-motif structure, were investigated to determine the effects of the gas composition, single-atom doping, and counter anions on the thermal stability of these clusters. We successfully synthesized crown-motif [PdAu 8 (PPh 3 ) 8 ][HPMo 12 O 40 ] (PdAu8-PMo12) and [PtAu 8 (PPh 3 ) 8 ][HPMo 12 O 40 ] (PtAu8-PMo12) salts with a cesium-chloride-type structure, which is the same as the [Au 9 (PPh 3 ) 8 ][PMo 12 O 40 ] (Au9-PMo12) structure. Thermogravimetry-differential thermal analysis/mass spectrometry analysis revealed that the crown-motif structure of Au9-PMo12 was decomposed at ∼475 K without weight loss to form Au nanoparticles. After structural decomposition, the ligands were desorbed from the sample. The ligand desorption temperature of Au9-PMo12 increased under 20% O 2 conditions because of the formation of Au nanoparticles and stronger interaction of the formed O=PPh 3 than PPh 3 . The Pd and Pt single-atom doping improved the thermal stability of the clusters. This improvement was due to the formation of a large bonding index of M-Au and a change in Au-PPh 3 bonding energy by heteroatom doping. Moreover, we found that the ligand desorption temperatures were also affected by the type of counter anions, whose charge and size influence the localized Coulomb interaction and cluster packing between the cationic ligand-protected metal clusters and counter anions.

Background: Because of the aging of the Japanese population, traumatic brain injuries (TBI) have increased in elderly adults. However, the effectiveness and prognosis of intensive treatment for geriatric TBI have not yet been determined. Thus, we used nationwide data from the Japan Neurotrauma Data Bank (JNTDB) projects to analyze prognostic factors for intensive and aggressive treatments., Methods: We analyzed 1,879 geriatric TBI cases (age ≥65 years) registered in four JNTDB projects: Project 1998 (P1998) to Project 2015 (P2015). Clinical features, use of aggressive treatment, and 6-month outcomes on the Glasgow Outcome Scale (GOS) were compared among study projects. Logistic regression was used to identify prognostic factors in aggressively treated patients., Results: The percentage of geriatric TBI cases significantly increased with time-P1998: 30.1%; Project 2004 (P2004): 34.6%; Project 2009 (P2009): 43.9%; P2015: 53.6%, p<0.0001). Use of aggressive treatment also significantly increased, from 67.0% in P1998 to 69.3% in P2015 (p<0.0001). Less invasive methods, such as trepanation and normothermic targeted temperature management, were more often chosen for geriatric patients. These efforts resulted in a significant decrease in the 6-month mortality rate, from 76.2% in P1998 to 63.1% in P2015 (p=0.0003), although the percentage of severely disabled patients increased, from 8.9% in P1998 to 11.1% in P2015 (p=0.0003). Intraventricular hemorrhage was the factor most strongly associated with unfavorable 6-month outcomes (OR 3.79, 95% CI 1.78-8.06, p<0.0001)., Conclusions: Less invasive treatments reduced mortality in geriatric TBI but did not improve functional outcomes. Patient age was not the strongest prognostic factor; thus, physicians should consider characteristics other than age.