Search

The hyperexpanded (CH 3NH 2)K 3C 60fulleride and its perdeuterated analogue were investigated by 1H and 2H NMR spectroscopy between room temperature and 4 K. Two phase transitions at TS= 220 K and TN= 11 K clearly were detected in the temperature dependence of the NMR line shapes, the spectral first ( M1) and second ( M2) moments, and the spin lattice relaxation times, T1. From 2H NMR line shape analysis, we found that the structural phase transition at TSwas driven by the freezing out of the discrete Markovian-type jump motion of the entire K +-ND 2CD 3unit that is characterized by an activation energy, Ea= 236(51) meV. Below TS, a sudden change in the temperature dependence of M1suggests the appearance of a small but nonzero spin density on the K +-NH 2CH 3unit. This could influence the electronic properties of the fulleride phase by modulating the strength of the exchange interactions between C 603−anions and controlling the width, W, of the t 1u-derived band. The 1H NMR spectra below TNshow significant line broadening consistent with the onset of long-range antiferromagnetic order. 1H NMR line shape calculations revealed the adoption of a type II magnetic structure with an ordering vector, q⃗II= (1/2, 1/2, 1/2) and individual C 603−magnetic moments of magnitude (∼0.7 µ B) aligned along the crystallographic a-axis. [ABSTRACT FROM AUTHOR]

Spherical magnetite nanoparticles (MNPs, ∼ 24 nm in diameter) were sequentially functionalized with trimethoxysilylpropyldiethylenetriamine (TMSPDT) and a synthetic DNA intercalator, namely, 9-chloro-4H-pyrido[4,3,2-kl]acridin-4-one (PyAcr), in order to promote DNA interaction. The designed synthetic pathway allowed control of the chemical grafting efficiency to access MNPs either partially or fully functionalized with the intercalator moiety. The newly prepared nanomaterials were characterized by a range of physicochemical techniques: FTIR, TEM, PXRD, and TGA. The data were consistent with a full surface coverage by immobilized silylpropyldiethylenetriamine (SPDT) molecules, which corresponds to ∼22 300 SPDT molecules per MNP and a subsequent (4740 − 2940) PyAcr after the chemical grafting step (i.e., ∼ 2.4 PyAcr/nm2). A greater amount of PyAcr (30 600) was immobilized by the alternative strategy of binding a fully prefunctionalized shell to the MNPs with up to 16.1 PyAcr/nm2. We found that the extent of PyAcr functionalization strongly affects the resulting properties and, particularly, the colloidal stability as well as the surface charge estimated by ζ-potential measurement. The intercalator grafting generates a negative charge contribution which counterbalances the positive charge of the single SPDT shell. The DNA binding capability was measured by titration assay and increases from 15 to 21.5 μg of DNA per mg of MNPs after PyAcr grafting (14−20% yield) but then drops to only ∼2 μg for the fully functionalized MNPs. This highlights that even if the size of the MNPs is obviously a determining factor to promote surface DNA interaction, it is not the only limiting parameter, as the mode of binding and the interfacial charge density are essential to improve loading capability. [ABSTRACT FROM AUTHOR]

In situ synchrotron X-ray powder diffraction is used to study the kinetics of cation ordering and ordered domain growth in the microwave dielectric electroceramic Ba3ZnTa2O9(BZT) with a time resolution of 15 s and processing temperatures of up to 1500 °C. This permits the measurement of the activation energy for cation ordering and the identification of different mechanisms for ordered domain growth, associated with the formation of the Ba8ZnTa6O24impurity phase due to zinc loss. [ABSTRACT FROM AUTHOR]

Two l-proline based homochiral frameworks synthesised via diffusion and solvothermal methods display distinct l-proline bonding modes, one N,O chelating and one O,O bridging with amine nitrogen not bound to the metal, with binding mode dependent upon the degree of protonation of the amino acid. [ABSTRACT FROM AUTHOR]

The zero-field muon-spin-relaxation (ZF-μ+SR) technique provides direct observation of the development of antiferromagnetic long range order in the hyperexpanded methylaminated fulleride salt, (CH3NH2)K3C60 below TN∼ 10 K—coherent ordering of the electronic magnetic moments leads to a local field of ∼25 G at the muon site at 1.2 K. [ABSTRACT FROM AUTHOR]

An 8-layer B-site deficient twinned hexagonal perovskiteBa8Ga4–xTa4+0.6xO24has been synthesized and its structureand microwave dielectric properties characterized. This hexagonalperovskite consists of eight close-packed BaO3layers stackedby a sequence of (ccch)2, where c and h refer to cubicand hexagonalBaO3layers, respectively. The Ba8Ga4–xTa4+0.6xO24ceramic materials exhibit composition-independent dielectric permittivityεr≈ 29, improved Qfvalue with the B-site vacancy content increase, and tunabletemperature coefficient of resonant frequency τffromnegative to positive. An optimum microwave dielectric performancewas achieved for Ba8Ga0.8Ta5.92O24: Qf≈ 29 000GHz and τf≈ 11 ppm/°C. The factors controllingthe microwave dielectric properties are discussed in comparison with8-layer twinned analogues and related 10-layer twinned hexagonal perovskitesbased on their structural and property data. [ABSTRACT FROM AUTHOR]

A new mixed-ligand three-dimensional metal−organic framework is reported, where one component, meso-iminodisuccinic acid, is formed in-situby the dimerization of aspartic acid under solvothermal conditions. The presence of a rigid pillaring co-ligand renders the framework truly porous and robust to guest loss. [ABSTRACT FROM AUTHOR]

The carboxylate ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy)-based on the strongly fluorescent long-lifetime pyrene core-affords a permanently microporous fluorescent metal-organic framework, [In2(OH)2(TBAPy)]∙(guests) (1), displaying 54% total accessible volume and excellent thermal stability. Fluorescence studies reveal that both 1 and TBAPy display strong emission bands at 471 and 529 nm, respectively, upon excitation at 390 nm, with framework coordination of the TBAPy ligands significantly increasing the emission lifetime from 0.089 to 0.110 ms. Upon desolvation, the emission band for the framework is shifted to lower energy: however, upon re-exposure to DMF the as-made material is regenerated with reversible fluorescence behavior. Together with the lifetime, the emission intensity is strongly enhanced by spatial separation of the optically active ligand molecules within the MOF structure and is found to be dependent on the amount and chemical nature of the guest species in the pores. The quantum yield of the material is found to be 6.7% and coupled with the fluorescence lifetime on the millisecond time scale, begins to approach the values observed for Eu(IIl)-cryptate-derived commercial sensors. [ABSTRACT FROM AUTHOR]

The first examples of anionic-neutral mixed ligand frameworks prepared from 1,3,5-benzenetrisbenzoate (BTB) and 4,4′-bipyridyl (bipy) are reported. Framework 1, of composition [Ni(HBTB)(bipy)]·(guests), is a triply interpenetrated (3,5)-connected grabinodal network that has a 1-D channel structure exhibiting permanent porosity. Framework 2, which was prepared under identical conditions but in the presence of toluene, has the formula [Ni3(BTB)2(EG)3(bipy)3]·(toluene) (where EG = ethylene glycol). 2is a dense phase of triply interpenetrated rare (3,4)-connected tfzbinodal networks that contains intercalated toluene in isolated voids. The primary influence for the formation of 2are numerous hydrophobic interactions between the internal framework surface and the included toluene guest molecule. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) technique is used to study the temperature evolution of the electronic and magnetic properties of the hyperexpanded fulleride (CH3NH2)K3C60in the temperature range 4−294 K. Unambiguous signatures for the development of large internal magnetic fields and a transition to an antiferromagnetic ground state below TN11 K are provided by the temperature dependence of the spin susceptibility, the EPR line width, and the position of the EPR line. The EPR results in the paramagnetic regime are indicative of an insulating electronic state, with localized S1/2 moments on the C603-ions. The accompanying complex evolution of the spin susceptibility, EPR line width, and g-factor anisotropy furthermore reveals that effects of electronic origin (t1uorbital order−disorder transition, crossover from static to dynamic Jahn−Teller distortions) in the vicinity of the structural transformation are important for the understanding of the exchange interactions between the fulleride ions. [ABSTRACT FROM AUTHOR]

A 21R-type mixed conducting oxygen-deficient hexagonal perovskite Ba7Y2Mn3Ti2O20was synthesized and its structure characterized by variable temperature neutron powder diffraction. The structure is characterized by the presence of both BaO2and BaO3layers. In the oxygen-stoichiometric material, the vacancies are ordered in c‘-BaO2layers. Extra oxygen is accommodated by intergrowth of the vacancy-ordered c‘-BaO2layers with cubic c-BaO3-xlayers (x≅ 1), which have disordered 2/3 oxygen occupancy. This material displays mixed electronic and oxide ionic conduction at high temperature, and the role of the two distinct and partially occupied anion sites within the BaO2layers in permitting the oxygen mobility is discussed. [ABSTRACT FROM AUTHOR]

A series of hypercrosslinked polymer networks has been synthesized by the self-condensation of bischloromethyl monomers such as dichloroxylene (DCX), 4,4‘-bis(chloromethyl)-1,1‘-biphenyl (BCMBP), and 9,10-bis(chloromethyl)anthracene (BCMA). These materials are predominantly microporous and exhibit Brunauer−Emmett−Teller (BET) surface areas of up to 1904 m2/g as measured by N2adsorption at 77.3 K (Langmuir surface area 2992 m2/g). Networks based on BCMBP exhibit a gravimetric storage capacity of 3.68 wt % at 15 bar and 77.3 K, the highest yet reported for an organic polymer. The micro- and mesostructure of the networks is explained by a combination of solid-state NMR, gas sorption measurements, pycnometry, and molecular simulations. The isosteric heat of sorption for H2on these materials is found to be in the range 6−7.5 kJ/mol. A molecular model is presented for a p-DCX network that simulates well certain key physical properties such as pore volume, pore width, absolute density, and bulk density. This model also predicts the isotherm shape and isosteric heat for H2sorption at 77.3 and 87.2 K but overestimates the absolute degree of H2uptake, most likely because of a degree of occluded, inaccessible porosity in the real physical samples. [ABSTRACT FROM AUTHOR]

The potential solid oxide fuel cell anode material Sr2MgMoO6adopts a √2 × √2 × 2 I superstructure of the simple perovskite cell, derived from an a0a0c-tilt system via distortion of the Mg- and Mo-centered octahedra. Reduction of Sr2MgMoO6appears to be correlated with antisite disorder at either point or extended antiphase defects. The degree of reduction is small at temperatures below 900 °C. Upon further reduction above 900 °C, Sr2MgMoO6begins to decompose into a reduced material modeled as an n 2 Ruddlesden−Popper phase with a significantly higher Mo:Mg ratio, MgO, and Mo. Diffraction data are consistent with the reduced material being significantly intergrown with the perovskite matrix. [ABSTRACT FROM AUTHOR]

The layered semiconductor Pt–HCa2Nb3O10can catalyze room temperature air oxidation of methyl orange. It is also more effective than Pt–WO3in catalyzing reaction of methanol with air. Pt–HCa2Nb3O10could find wide application as a mild oxidizing catalyst. [ABSTRACT FROM AUTHOR]

The synthesis of fluorescent water-soluble gold nanoparticles by the reduction of a gold salt in the presence of a designed polymer ligand is described, the size and fluorescence of the particles being controlled by the polymer to gold ratio; the most fluorescent nanomaterial has a 3% quantum yield, a 1.1 nm gold core and a 6.9 nm hydrodynamic radius. [ABSTRACT FROM AUTHOR]

Post-synthetic derivatisation of a porous material produces a functionalized material that binds the metal complex V(O)acac2, in contrast to the unfunctionalized precursor, which is inactive for complex binding. [ABSTRACT FROM AUTHOR]

Protonation of chiral porous materials introduces a Brønsted acid centre, the structure of which is unique to the heterogeneous phase requiring pore wall confinement for stable isolation. [ABSTRACT FROM AUTHOR]

Ligand flexibility permits framework rearrangement upon evacuation and gas uptake in a new family of porous MOFs. [ABSTRACT FROM AUTHOR]