Structural and magnetic characterization of the elusive Jahn-Teller active NaCrF3

We report the structural and magnetic characterization of the elusive Jahn- Teller active compound NaCrF3

Structure and magnetic property of potassium intercalated pentacene: observation of superconducting phase in KxC22H14

We report the results from systematic investigations on the structure and magnetic properties of potassium intercalated pentacene as a function of potassium content, K x C22H14 (1  ≤  x  ≤  3). Synchrotron radiation powder x-ray diffraction technique revealed that there are two different stable phases can be obtained via potassium intercalation, namely, K1C22H14 phase and K3C22H14 phase. Structural phase transition was induced when the potassium content was increased to the nominal value x  =  3. This phase transition is accompanied by drastic change in their magnetic property, where those samples with compositions K1C22H14 shows ferromagnetic behavior and those with near K3C22H14 lead to observation of superconductivity with transition temperature, T c, of 4.5 K. It is first time that superconductivity was observed in linear oligoacenes. Both magnetization study and synchrotron radiation powder x-ray diffraction clearly indicates that the superconducting phase belong to K3C22H14 as a result of phase transition from triclinic to monoclinic structure induced by chemical doping

Reversible adsorption and confinement of nitrogen dioxide within a robust porous metal-organic framework

Nitrogen dioxide (NO2) is a major air pollutant causing significant environmental and health problems. We report reversible adsorption of NO2 in a robust metal–organic framework. Under ambient conditions, MFM-300(Al) exhibits a reversible NO2 isotherm uptake of 14.1 mmol g−1, and, more importantly, exceptional selective removal of low-concentration NO2 (5,000 to <1 ppm) from gas mixtures. Complementary experiments reveal five types of supramolecular interaction that cooperatively bind both NO2 and N2O4 molecules within MFM-300(Al). We find that the in situ equilibrium 2NO2 ↔ N2O4 within the pores is pressure-independent, whereas ex situ this equilibrium is an exemplary pressure-dependent first-order process. The coexistence of helical monomer–dimer chains of NO2 in MFM-300(Al) could provide a foundation for the fundamental understanding of the chemical properties of guest molecules within porous hosts. This work may pave the way for the development of future capture and conversion technologies

Synthesis, crystallization, X-ray structural characterization and solid-state assembly of a cyclic hexapeptoid with propargyl and methoxyethyl side chains

The synthesis and the structural characterization of a cyclic hexapeptoid with four methoxyethyl and two propargyl side chains have disclosed the presence of a hydrate crystal form [form (I)] and an anhydrous crystal form [form (II)]. The relative amounts of form (I) and form (II) in the as-purified product were determined by Rietveld refinement and depend on the purification procedures. In crystal form (I), peptoid molecules assemble in a columnar arrangement by means of side-chain-to-backbone C CH OC hydrogen bonds. In the anhydrous crystal form (II), cyclopeptoid molecules form ribbons by means of backbone-to-backbone CH2 OC hydrogen bonds, thus mimicking -sheet secondary structures in proteins. In both crystal forms side chains act as joints among the columns or the ribbons and contribute to the stability of the whole solid-state assembly. Water molecules in the hydrate crystal form (I) bridge columns of cyclic peptoid molecules, providing a more efficient packing

O3–NaxMn1/3Fe2/3O2 as a positive electrode material for Na-ion batteries: structural evolutions and redox mechanisms upon Na+ (de)intercalation

The electrochemical properties of the O3-type NaxMn1/3Fe2/3O2 (x = 0.77) phase used as positive electrode material in Na batteries were investigated in the 1.5–3.8 V, 1.5–4.0 V and 1.5–4.3 V ranges. We show that cycling the Na cells in a wider voltage range do not induce a significant gain on long term cycling as the discharge capacities reached for the three experiments are identical after the 14th cycle. The structural changes the material undergoes from 1.5 V (fully intercalated state) to 4.3 V were investigated by operando in situ X-ray powder diffraction (XRPD) and were further characterized by ex situ synchrotron XRPD. We show that the low amount of Mn3+ ions (≈33% of total Mn+ ions) is enough to induce a cooperative Jahn–Teller effect for all MO6 octahedra in the fully intercalated state. Upon deintercalation the material exhibits several structural transitions: O′3 → O3 → P3. Furthermore, several residual phases are observed during the experiment. In particular, a small part of the O3 type is not transformed to P3 but is always involved in the electrochemical process. To explain this behaviour the hypothesis of an inhomogeneity, which is not detected by XRD, is suggested. All phases converge into a poorly crystallized phase for x ≈ 0.15. The short interslab distance of the resulting phase strongly suggests an octahedral environment for the Na+ ions. X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy were used to confirm the activity of the Mn4+/Mn3+ and Fe4+/Fe3+ redox couples in the low and high voltage regions, respectively. 57Fe Mössbauer spectroscopy also showed an increase of the disorder into the material upon deintercalation