A tetragonal form of dysprosium orthomolybdate at room temperature

In the present tetragonal modification of dysprosium orthomolybdate, Dy₂(MoO₄)₃, the Dy, one Mo and one O atom are located on a mirror plane with Wyckoff symbol 4e, while another Mo atom is located on a fourfold inverse axis, Wyckoff symbol 2a. A single crystal was selected from a polycrystalline mixture of the Dy₂O₃–ZrO₂–MoO₃ system and was stable at room temperature for at least three months. The structure refinement does not indicate the presence of Zr on the Dy sites (to within 1% accuracy). Thus, the stabilization of the tetragonal form is due to disordered positions for a second O atom and split positions for a third O atom that also maintain the DyO₇ coordination, which is not expected for short Dy—O distances [2.243 (6)–2.393 (5) Å].     

Lasing mechanism of ZnO nanowires/nanobelts at room temperature

ZnO has become the focus of photonics and optoelectronic research. We prepared pure Mn(II) doped ZnO nanowires with a controlled reduction reaction by carbon in an asymmetrical tube. Careful time-resolved photoluminescence experimental study indicates three types of lasing mechanisms: exciton-exciton interaction, bipolaronic exciton condensation, and plasma; these exist in different ZnO nanowires, which can be changed by doping Mn in ZnO nanowire. The transformation between varied mechanisms is discussed in detail with their spectral behaviors. These results are important in the design of future violet-blue luminescence and display devices.     

Rational tuning of melting entropies for designing luminescent lanthanide-containing thermotropic liquid crystals at room temperature

The connection of twelve peripheral and divergent dodecyloxy chains to a central tridentate aromatic binding unit provides the dodecacatenar ligand L11, for which room-temperature mesomorphism is detected. An enthalpically unbalanced large melting entropy (DeltaSmL11=226 J mol(-1) K(-1)) results from the programmed microsegregation induced in the crystalline phase, a phenomenon which is maintained in the associated lanthanide complexes [Ln(L11)(NO3)3] and [Ln(L11)(CF3CO2)3]2. Low-temperature melting processes (-43相似文献   

Fabrication of upended taper-shaped cuprous thiocyanate arrays on a copper surface at room temperature

A new strategy has been well designed to form upended taper-shaped cuprous thiocyanate (hereafter abbreviated as CuCNS) arrays on a copper substrate with use of a simple solution-phase method at room temperature. This method consists of a liquid-solid reaction between a solution of thiocyanate ammonium and the copper substrate itself in the assistance of formamide. Novel CuCNS arrays are approximately perpendicular to copper substrate surfaces. Every single crystal shows an upended taper-like morphology (i.e., the tip end points into the surface of copper substrate and the other big end of the taper exposes out, like a dart thrusting into the copper substrate). On the basis of structure and chemical bond analysis, CuCNS crystals tend to grow along the c-axis, which is essential for the formation of CuCNS arrays on a copper substrate. This approach also provides a facile strategy to produce different patterns on different copper substrates, which may be applicable to the synthesis of other inorganic materials with various potential applications.     

Xenon porometry at room temperature

Xenon porometry is a method in which porous material is immersed in a medium and the properties of the material are studied by means of 129Xe nuclear magnetic resonance (NMR) of xenon gas dissolved in the medium. For instance, the chemical shift of a particular signal (referred to as signal D) arising from xenon inside small pockets formed in the pores during the freezing of the confined medium is highly sensitive to the pore size. In the present study, we show that when naphthalene is used as the medium the pore size distribution of the material can be determined by measuring a single one-dimensional spectrum near room temperature and converting the chemical shift scale of signal D to the pore radius scale by using an experimentally determined correlation. A model has been developed that explains the curious behavior of the chemical shift of signal D as a function of pore radius. The other signals of the spectra measured at different temperatures have also been identified, and the influence of xenon pressure on the spectra has been studied. For comparison, 129Xe NMR spectra of pure xenon gas adsorbed to porous materials have been measured and analyzed.     

Cationic polymerization of isobutylene at room temperature

This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile‐ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups—the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Crystallization-induced phosphorescence of benzils at room temperature

Efficient room temperature phosphorescence (RTP) is rarely observed in pure organic luminogens. However, we have newly observed that benzil and its derivatives are nonluminescent in solvents and thin layer chromatography (TLC) plates, but become highly phosphorescent in crystal state at room temperature, exhibiting typical crystallization-induced phosphorescence (CIP) characteristics. The CIP phenomenon is ascribed to the restriction of intramolecular rotations in crystals owing to effective intermolecular interactions. Such intermolecular interactions greatly rigidify the molecular conformation and significantly decrease the nonradiative deactivation channels of the triplet excitons, thus giving boosted phosphorescent emission at room temperature.     

Thermal properties at room temperature of polytetrafluoroethylene

Through Differential Scanning Calorimetry (DSC), at least three room temperature transitions are clearly observable for native polytetrafluoroethylene (PTFE). The influence of the thermal history on the room temperature transitions has been investigated. Possible interpretations for the lowest room temperature transition are suggested.

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Zusammenfassung Bei der Untersuchung von nativen Polytetrafluoroethylen (PTFE) lassen sich im Raumtemperaturbereich zumindest drei Umwandlungen eindeutig beobachten. Der Einfluss der termischen Vorgeschichte von PTFE Proben auf die Umwandlungen im Raumtemperaturbereich wurde untersucht.Mögliche ErklÄrungen für den tiefstliegenden übergang im genannten Temperaturbereich werden vorgeschlagen.

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Dr. G. Ajroldi and Prof. G. Guerra are gratefully acknowledged for useful advice and stimulating discussions.     

Synthesis of zeolite nanocrystals at room temperature

Zeolite A nanoparticles were synthesized under room-temperature conditions from a very reactive organic-template-free gel system. The optimization of the syntheses parameters, namely, the composition of the initial system and the careful choice of the reactants, allowed the crystallization to be accomplished within 3 days. At this stage the individual zeolite crystals were in the range of 100-300 nm without well-developed crystal faces. The prolongation of the synthesis time up to 10 days led to formation of larger well-faceted cubic crystals averaging about 400-500 nm in size. The high-resolution transmission electron microscopy (HRTEM) study revealed that a thin layer of amorphous material covers the zeolite particles acting as a binder between individual zeolite crystals. The postsynthesis treatment of the product in NH(3) media under ultrasonic radiation disintegrated the loosely attached zeolite particles and decreased the fraction of zeolite A particles with low colloidal stability. The employed approach, however, did not result in complete disintegration of aggregated crystals. The zeolite crystals obtained under ambient conditions were characterized by XRD, SEM, dynamic light scattering, and N(2) adsorption measurements.     

A 2-D dysprosium glutarate exhibiting slow magnetic relaxation and luminescent properties

Abstract

A 2-D dysprosium glutarate [Dy₂(glu)₃(phen)₂]_n (1, glu?=?glutarate, phen =1,10-phenanthroline) has been synthesized from the hydrothermal reaction of DyCl₃, glutaric acid, and phen ligand. Compound 1 displays a classical 2-D (4,4) grid structure constructed by the linkages of Dy³⁺ ions and three types of glutarate ligands. Compound 1 shows slow magnetic relaxation and luminescent properties. Although some lanthanide glutarates have been reported, they do not exhibit slow magnetic relaxation properties. Compound 1 offers the only example of a dysprosium coordination polymer with field-induced single-molecule magnets (SMMs) based on aliphatic dicarboxylic acids in the absence of ancillary aromatic carboxylic acids.     

Hydroboration with pyridine borane at room temperature

Treatment of pyridine borane (Py.BH3) with iodine, bromine, or strong acids affords activated Py.BH2X complexes that are capable of hydroborating alkenes at room temperature. Evidence is presented for an unusual hydroboration mechanism involving leaving group displacement. In contrast to THF.BH3, hydroboration with Py.BH2I selectively affords the monoadducts. The crude hydroboration products are converted into synthetically useful potassium alkyltrifluoroborate salts upon treatment with methanolic KHF2.     

Transition-metal-free C-arylation at room temperature by arynes

A facile, fluoride-induced transition-metal-free chemoselective α-arylation of β-dicarbonyl compounds (malonamide esters) at room temperature using aryne intermediates has been demonstrated. Selective mono- or diarylation and generation of a quaternary benzylic stereocenter have also been achieved. The methodology will be highly useful for the synthesis of a library of CNS depressant barbiturate drugs like Phenobarbital.     

Polyurethane adhesive composition cured at room temperature

The influence of polyfunctional hydroxyl-containing oligomer on the rheological, physicomechanical, and adhesive properties of polyurethane composite based on multicomponent oligomer blend and polyisocyanate is investigated. The kinetics of curing is investigated by the viscometric method, and the composition lifetime is determined. It is shown that the polyurethanes under investigation can be used as fast-curing adhesive composites of cold curing operating in a temperature interval of up to +90°C.