New half-sandwich molybdenum complexes [Mo(CpBz)Cl 2 (O)] (1), [{Mo(CpBz)(O) 2 } 2 (µ−O)] (5) and [Mo(CpBz)Cl 2 ] 2 (6) (CpBz = C 5 (CH 2 Ph) 5 ), the tungsten derivative [W(CpBz)Cl(O) 2 ] (3) and a high yield synthesis of [Mo(CpBz)Cl(O) 2 ] (2), are described. The molecular structures and cyclic voltammetry measurements of 1 and 2 and a comparative study of various molybdenum dioxo complexes as olefin epoxidation catalyst precursors are also presented. The performance of [Mo(CpPr i 4 )Cl(O) 2 ] (9) as cyclooctene epoxidation catalyst using TBHP as oxidant was determined and compared with other [MoCp'Cl(O) 2 ] complexes (Cp' = C 5 H 5 (7), C 5 Me 5 (8), CpBz (2)) to assess the activity dependence on the ring-substituents. Under the same experimental conditions, bimetallic compounds [{MoCp'(O) 2 } 2 (µ−O)] (Cp' = CpBz (5), Cp* (10), CpBu t 3 (11), CpPr i 4 (12)) have been tested and [CpMoO 2 ] 2 O was checked in aqueous solution, with H 2 O 2 and TBHP as oxidant. Finally, [Mo(CpBz)(CO) 3 CH 3 ] ( 4) was used as a catalyst precursor for cyclooctene epoxidation in the presence of TBHP. The analogy between the behaviors displayed by this complex and complex 2 is discussed.

This is the first report of a multifunctional separator for potassium‐metal batteries (KMBs). Double‐coated tape‐cast microscale AlF3 on polypropylene (AlF3@PP) yields state‐of‐the‐art electrochemical performance: symmetric cells are stable after 1000 cycles (2000 h) at 0.5 mA cm−2 and 0.5 mAh cm−2, with 0.042 V overpotential. Stability is maintained at 5.0 mA cm−2 for 600 cycles (240 h), with 0.138 V overpotential. Postcycled plated surface is dendrite‐free, while stripped surface contains smooth solid electrolyte interphase (SEI). Conventional PP cells fail rapidly, with dendrites at plating, and “dead metal” and SEI clumps at stripping. Potassium hexacyanoferrate(III) cathode KMBs with AlF3@PP display enhanced capacity retention (91% at 100 cycles vs 58%). AlF3 partially reacts with K to form an artificial SEI containing KF, AlF3, and Al2O3 phases. The AlF3@PP promotes complete electrolyte wetting and enhances uptake, improves ion conductivity, and increases ion transference number. The higher of K+ transference number is ascribed to the strong interaction between AlF3 and FSI− anions, as revealed through 19F NMR. The enhancement in wetting and performance is general, being demonstrated with ester‐ and ether‐based solvents, with K‐, Na‐, or Li‐ salts, and with different commercial separators. In full batteries, AlF3 prevents Fe crossover and cycling‐induced cathode pulverization.

Reactions of titanium and yttrium trichlorides with 1 equiv of the sodium or potassium salts of the diamine bis(phenolate) H2 tBu2O2NN′ (Me2NCH2CH2-(CH2-2-HO-3,5-C6H2 tBu2)2) led to formation of [TiCl(tBu2O2NN′)(L)] (L = THF, 1; py, 2) and [YCl(tBu2O2NN′)(DME)], 3. Reactions of 1 or 3 with MCH2-(2-NMe2)C6H4 and with M[2-(CH2NMe2)C6H4] (M = Li, K) led to [Ti(tBu2O2NN′)(κ2-(CH2C6H4NMe2))], 5, [Y(tBu2O2NN′)(κ2-(CH2C6H4NMe2))], 6, and [Y(tBu2O2NN′)(κ2-(C6H4CH2NMe2))], 7. [Y(tBu2O2NN′)N(SiMe3)2], 4, was obtained from 3 and KN(SiMe3)2, whereas [(Y(tBu2O2NN′)(CH2SiMe3))2(μ4-O)(μ3-Li)2], 8, formed from reaction of 3 and LiCH2SiMe3. The reaction of 7 with 1 equiv of CH3CN gave [Y(tBu2O2NN′)(NC(CH3)C6H4CH2NMe2)], 10, which displays a chelating ketimide ligand formed by nitrile insertion in the Y−Ph bond. Further reaction with CH3CN led to [Y(tBu2O2NN′)(κ2-(N(H)C(CH3)C(H)C(C6H4CH2NMe2)N(H)], 9, the formation of which involves an imine−enamine tautomerism followed by a second nitrile insertion and 1,3-hydrogen shift. The reaction of 1 with CH3CN gave [TiCl(tBu2O2NN′)(NCCH3)], which upon heating converts to a new paramagnetic species that is likely a chloride-bridged Ti(III) dimer. The EPR study performed reveals that bis(phenolate) Ti(III) complexes do not promote nitrile coupling reactions by electron transfer. The solid state molecular structures of 1−9 revealed that in all the complexes the bis(phenolate) ligand is coordinated to the metal center by the two oxygen atoms and the two nitrogen atoms with trans phenolate arrangement.

Here, we employ a combination of 27 Al solidstate nuclear magnetic resonance (SSNMR) and conventional spectroscopic and microscopic techniques to investigate the structural evolution of aqueous aluminum precursors to a uniform and smooth aluminum oxide film. The route involves no organic ligands and relies on dehydration, dehydroxylation, and nitrate loss for condensation and formation of the threedimensional aluminum oxide structure. Local chemical environments are tracked as films evolve over the temperature range 200−1100 °C. 27 Al SSNMR reveals that Al centers are predominantly four-and five-coordinate in amorphous films annealed between 200 and 800 °C and four-and six-coordinate in crystalline phases that form above 800 °C. The Al coordination of the aqueous-deposited aluminum oxide films are compared to data from SSNMR studies on vapor-phasedeposited aluminum oxide thin films. Additionally, dielectric constants of aluminum oxide-based capacitors are measured and correlated with the SSNMR results. Aluminum oxide is an important material for protective coatings, catalysis, and microelectronic applications. For the latter application, amorphous materials are preferred, but a lack of long-range order complicates structural characterization and determination of structure−property relationships. Solution deposition approaches are attractive alternatives to traditional vapor-phase deposition methods because precursors are commonly stable in air, and they enable printing and direct lithographic patterning on common semiconductor wafers as well as large-area and flexible substratesuseful for scale-up to applications in windows and photovoltaic devices.

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Room-temperature ionic liquids (RTILs) hold promise for applications in electric double layer capacitors (EDLCs), owing to a much wider potential window, lower vapor pressure, and better thermal and chemical stabilities compared to conventional aqueous and organic electrolytes.However, because the low diffusivity of ions in neat RTILs negates the EDLCs' advantage of high power density, the ionic liquids are often used in mixture with organic solvents. In this study, we measured the diffusivity of cations and anions in RTIL, 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) ([BMIM + ][TFSI -]), mixed with 10 organic solvents, by using the pulsed-field gradient NMR method. The ion diffusivity was found to follow that of neat solvents, and in most studied solvents showed an excellent agreement with the predicted values reported in the recent molecular dynamics (MD) study [

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Potassium‐Metal Batteries In article number 2105855, Pengcheng Liu, David Mitlin, and co‐workers report a multifunctional separator for potassium‐metal batteries. The cover depicts two foxes playfully hopping across an ancient arctic river while carrying glowing ions in their mouths. The potassiphilic aluminum fluoride crystals, which are the key functional aspect of the separator, are the crystallographic ice sheets regularly arranged on the surface. The frigid water beneath represents the electrolyte. In the background are frozen mountains, which are the potassium‐metal dendrites that would form without the functional separator.