Electrocatalytic properties, X-ray crystallographic studies, and infrared spectroelectrochemistry (IR-SEC) of Mn(bpy-tBu)(CO)3Br and Mn(bpy-tBu)(CO)3(MeCN)(OTf) are reported. Addition of Brönsted ...acids to CO2-saturated solutions of these Mn complexes and subsequent reduction of the complexes lead to the stable and efficient production of CO from CO2. Unlike the analogous Re catalysts, these Mn catalysts require the addition of Brönsted acids for catalytic turnover. Current densities up to 30 mA/cm2 were observed during bulk electrolysis using 5 mM Mn(bpy-tBu)(CO)3Br, 1 M 2,2,2-trifluoroethanol, and a glassy carbon working electrode. During bulk electrolysis at −2.2 V vs SCE, a TOF of 340 s–1 was calculated for Mn(bpy-tBu)(CO)3Br with 1.4 M trifluoroethanol, corresponding to a Faradaic efficiency of 100 ± 15% for the formation of CO from CO2, with no observable production of H2. When compared to the analogous Re catalysts, the Mn catalysts operate at a lower overpotential and exhibit similar catalytic activities. X-ray crystallography of the reduced species, Mn(bpy-tBu)(CO)3−, shows a five-coordinate Mn center, similar to its rhenium analogue. Three distinct species were observed in the IR-SEC of Mn(bpy-tBu)(CO)3Br. These were of the parent Mn(bpy-tBu)(CO)3Br complex, the dimer Mn(bpy-tBu)(CO)32, and the Mn(bpy-tBu)(CO)3− anion.
There is intense interest in sodium-ion batteries as an alternative to lithium-ion batteries for electric storage applications because of the low-cost and abundant sodium resources. Na0.67Ni0.33–x Mg ...x Mn0.67O2 compounds (x = 0, 0.02, 0.05, 0.1, or 0.15) were prepared by a sol–gel method and used as a cathode for sodium-ion batteries. The X-ray powder diffraction measurements demonstrated that the obtained samples have a pure P2 phase. Na0.67Ni0.23Mg0.1Mn0.67O2 delivers an initial reversible capacity of 105 mAh g–1 in the potential region from 2.0 to 4.5 V at a charge/discharge current density of 48 mA g–1. Moreover, the cyclability is improved by doping Mg. The capacity of Na0.67Ni0.23Mg0.1Mn0.67O2 can remain at approximately 84.9 mAh g–1 at a current density of 48 mA g–1 after 100 cycles. The improved high rate performance of Na0.67Ni0.23Mg0.1Mn0.67O2 was attributed to the increased lattice parameters and d spacing of the Na+ layer. Therefore, Mg-doped Na0.67Ni0.23Mg0.1Mn0.67O2 is a promising cathode for sodium-ion batteries with excellent rate and cyclic performance.
A high-nuclearity 3d–4f cluster of Gd30CoII 6CoIII 6(OH)56(NO3)12(CH3COO)30(H2O)30·(NO3)22·(en)3·(H2O)3 (1) was synthesized through the reaction of Gd(NO3)3·6H2O, Co(NO3)2·6H2O, and sodium acetate ...in a mixture of ethanediamine (en), ethanol, and deionized water. The cluster core in 1 features a double-shell structure with a Co12 icosahedron encapsulating a Gd30 icosidodecahedron. A magnetic study reveals that separating Co2+ ions with Gd3+ ions can effectively reduce the magnetic interaction of 3d–4f clusters. Significantly, the magnetocaloric effect (MCE) of 1 at 2 K and 7 T is up to 44.7 J kg–1 K–1, the largest MCE reported to date in the 3d–4f metal clusters.
The new 3D Hofmann-type coordination polymer Fe(dpyu){Pt(CN)4}·9H2O dpyu = 1,3-di(pyridin-4-yl)urea exhibits reversible interchange between two- and one-step spin-crossover behavior, associated ...with desorption/resorption of lattice water molecules. Solvent water removal also induces an increase of the spin-transition temperature, indicating strong lattice cooperativity, observed for the first time in a 3D Hofmann-type coordination polymer.
The double perovskite CaMnTi2O6, is a rare A-site ordered perovskite oxide that exhibits a sizable ferroelectric polarization and relatively high Curie temperature. Using first-principles ...calculations combined with detailed symmetry analyses, we identify the origin of the ferroelectricity in CaMnTi2O6. We further explore the material properties of CaMnTi2O6, including its ferroelectric polarization, dielectric and piezoelectric responses, magnetic order, electronic structure, and optical absorption coefficient. It is found that CaMnTi2O6 exhibits room-temperature-stable ferroelectricity and moderate piezoelectric responses. Moreover, CaMnTi2O6 is predicted to have a semiconducting energy band gap similar to that of BiFeO3, and its band gap can further be tuned via distortions of the planar Mn–O bond lengths. CaMnTi2O6 exemplifies a new class of single-phase semiconducting ferroelectric perovskites for potential applications in ferroelectric photovoltaic solar cells.
A new Mn(II) metal–organic framework (MOF) 1 was synthesized by the combination of 4,4,4-trifluoro-1-(4-(pyridin-4-yl)phenyl)butane-1,3-dione (L) and Mn(OAc)2 in solution. 1 features a ...threefold-interpenetrating NbO net containing honeycomb-like channels, in which the opposite Mn(II)···Mn(II) distance is 23.5075(10) Å. Furthermore, 1 can be an ideal platform to support Pd–Au bimetallic alloy nanoparticles to generate a composite catalytic system of Pd–Au@Mn(II)-MOF (2). 2 can be a highly active bifunctional heterogeneous catalyst for the one-pot tandem synthesis of imines from benzyl alcohols and anilines and from benzyl alcohols and benzylamines.
A new composite photocatalyst Ag/AgBr/WO3·H2O was synthesized by reacting Ag8W4O16 with HBr and then reducing some Ag+ ions in the surface region of AgBr particles to Ag nanoparticles via the ...light-induced chemical reduction. Ag nanoparticles are formed from AgBr by the light-induced chemical reduction reaction. The Ag/AgBr particles are on the surface of WO3·H2O and have irregular shapes with sizes varying between 63 and 442 nm. WO3·H2O appears as flakes about 31 nm thick and 157−474 nm wide. The as-grown Ag/AgBr/WO3·H2O sample shows strong absorption in the visible region because of the plasmon resonance of Ag nanoparticles in Ag/AgBr/WO3·H2O. The ability of this compound to destroy E. coli and oxidize methylic orange under visible light was compared with those of other reference photocatalysts. Ag/AgBr/WO3·H2O is a highly efficient photocatalyst under visible light. The Ag/AgBr/WO3·H2O samples recovered from repeated photooxidation experiments are almost identical to the as-prepared samples, proving the stability of Ag/AgBr/WO3·H2O sample.
A photoisomerizable diarylethene-derived ligand, phen*, has been successfully introduced into a spin-crossover iron(II) complex, Fe(H2B(pz)2)2phen* (1; pz =1-pyrazolyl). A ligand-based ...photocyclization (photocycloreversion) in 1 modifies the ligand field, which, in turn, results in a highly efficient paramagnetic high-spin → diamagnetic low-spin (low-spin → high-spin) transition at the coordinated FeII ion. The reversible photoswitching of the spin states, and thus the associated magnetic properties, has been performed in solution at room temperature and has been directly monitored by measuring the magnetic susceptibility via the Evans method. The observed spin-state photoconversion in 1 exceeds 40%, which is the highest value for spin-crossover molecular switches in solution at room temperature reported to date. The photoexcited state is extraordinarily thermally stable, showing a half-time of about 18 days in solution at room temperature. Because of the outstanding photophysical properties of diarylethenes, including single-crystalline photochromism, molecular switch 1 may offer a promising platform for controlling the magnetic properties in the solid state and ultimately at the single-molecule level with light at room temperature.
New sets of Lennard-Jones and Buckingham potentials have been developed to be used in classical molecular dynamics simulations of Ln3+-containing systems for the whole lanthanoid series. The ...force-field parameters have been refined by directly comparing the hydration structure obtained from the simulations with the extended X-ray absorption fine structure (EXAFS) experimental data, in order to reproduce Ln3+-water EXAFS experimentally inferred mean distances. Analysis of the simulation results has shown that both Lennard-Jones and Buckingham potentials are able to properly describe the radial distribution of water molecules around the Ln3+ ions, the smooth decrease of the hydration number along the lanthanoid series, as well as the geometry of the first-shell hydration complex formed by Ln3+ ions in water. The newly optimized interaction potential parameters can be used in conjunction with force fields available in the literature to investigate the solvation properties of Ln3+ ions in different disordered systems.
Materials that demonstrate a multichannel controllable color change in response to external stimuli are fascinating for their potential applications in sensoring and displaying devices. Herein we ...report a FeII spin-crossover (SCO) compound that exhibits both solvatochromism and thermochromism under an ambient environment. This Hofmann-type compound possesses two different pores where the solvent guests can be removed in a two-step process. Because the loss of solvent guests modifies the spin state of magnetic centers, an unusual yellow–red–yellow two-step color change of crystals was detected. Moreover, because of the strong cooperativity of the spin centers, a dramatic red-to-yellow color change of crystals in response to a minute thermal perturbation around 303 K is triggered by an abrupt spin transition of the metal centers. The multichannel controllable dramatic color change demonstrated in the present compound highlights the sensoring and displaying roles of SCO materials.
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