New Type Of Precursor Research Articles

4-Vinylbenzodioxinones as a new type of precursor for palladium-catalyzed (4+3) cycloaddition of azomethine imines.

In this paper, benzo-fused cyclic carbonates were designed and synthesized as a new type of precursor of π-allylpalladium zwitterionic intermediates, and were applied in Pd-catalyzed diastereo- and enantioselective (4+3) cycloaddition with C,N-cyclic azomethine imines, leading to various biologically important 1,3,4-benzoxadiazepine derivatives in 43-99% yields with 6 : 1 to >20 : 1 dr and up to 95% ee.

Development of Ferromagnetic Materials Containing Co2P, Fe2P Phases from Organometallic Dendrimers Precursors.

The development of synthesis methods to access advanced materials, such as magnetic materials that combine multimetallic phosphide phases, remains a worthy research challenge. The most widely used strategies for the synthesis of magnetic transition metal phosphides (TMPs) are organometallic approaches. In this study, Fe-containing homometallic dendrimers and Fe/Co-containing heterometallic dendrimers were used to synthesize magnetic materials containing multimetallic phosphide phases. The crystalline nature of the nearly aggregated particles was indicated for both designed magnetic samples. In contrast to heterometallic samples, homometallic samples showed dendritic effects on their magnetic properties. Specifically, saturation magnetization (Ms) and coercivity (Hc) decrease as dendritic generation increases. Incorporating cobalt into the homometallic dendrimers to prepare the heterometallic dendrimers markedly increases the magnetic properties of the magnetic materials from 60 to 75 emu/g. Ferromagnetism in homometallic and heterometallic particles shows different responses to temperature changes. For example, heterometallic samples were less sensitive to temperature changes due to the presence of Co2P in contrast to the homometallic ones, which show an abrupt change in their slopes at a temperature close to 209 K, which appears to be related to the Fe2P ratios. This study presents dendrimers as a new type of precursor for the assembly of magnetic materials containing a mixture of iron- and cobalt-phosphides phases with tunable magnetism, and provides an opportunity to understand magnetism in such materials.

2D Nanoporous Fe-N/C Nanosheets as Highly Efficient Non-Platinum Electrocatalysts for Oxygen Reduction Reaction in Zn-Air Battery.

It is an ongoing challenge to fabricate nonprecious oxygen reduction reaction (ORR) catalysts that can be comparable to or exceed the efficiency of platinum. A highly active non-platinum self-supporting Fe-N/C catalyst has been developed through the pyrolysis of a new type of precursor of iron coordination complex, in which 1,4-bis(1H-1,3,7,8-tetraazacyclopenta(1)phenanthren-2-yl)benzene (btcpb) functions as a ligand complexing Fe(II) ions. The optimal catalyst pyrolyzed at 700 °C (Fe-N/C-700) shows the best ORR activity with a half-wave potential (E1/2 ) of 840 mV versus reversible hydrogen electrode (RHE) in 0.1 m KOH, which is more positive than that of commercial Pt/C (E1/2 : 835 mV vs RHE). Additionally, the Fe-N/C-700 catalyst also exhibits high ORR activity in 0.1 m HClO4 with the onset potential and E1/2 comparable to those of the Pt/C catalyst. Notably, the Fe-N/C-700 catalyst displays superior durability (9.8 mV loss in 0.1 m KOH and 23.6 mV loss in 0.1 m HClO4 for E1/2 after 8000 cycles) and better tolerance to methanol than Pt/C. Furthermore, the Fe-N/C-700 catalyst can be used for fabricating the air electrode in Zn-air battery with a specific capacity of 727 mA hg-1 at 5 mA cm-2 and a negligible voltage loss after continuous operation for 110 h.

Mechanical mixtures of metal oxides and phosphorus pentoxide as novel precursors for the synthesis of transition-metal phosphides

This study presents a new type of precursor, mechanical mixtures of metal oxides (MOs) and phosphorus pentoxide (P2O5) are used to synthesize Ni2P, Co2P and MoP phosphides by the H2 reduction method. In addition, this is first report of common solid-state P2O5 being used as a P source for the synthesis of metal phosphides. The traditional precursors are usually prepared via a complicated preparation procedure involving dissolution, drying and calcination steps. However, these novel MOs/P2O5 precursors can be obtained only by simple mechanical mixing of the starting materials. Furthermore, unlike the direct transformation from amorphous phases to phosphides, various specific intermediates were involved in the transformation from MOs/P2O5 to phosphides. It is worthy to note that the dispersions of Ni2P, Co2P and MoP obtained from MOs/P2O5 precursors were superior to those of the corresponding phosphides prepared from the abovementioned traditional precursors. It is suggested that the morphology of the as-prepared metal phosphides might be inherited from the corresponding MOs. Based on the results of XRD, XPS, SEM and TEM, the formation pathway of phosphides can be defined as MOs/P2O5 precursors → complex intermediates (metals, metal phosphates and metal oxide-phosphates) → metal phosphides.

Influence of cryogenic drying conditions on hierarchical porous structure of aluminum oxide systems

Highly porous alumina systems were aimed to produce by low energy-consuming sol–gel and freeze drying techniques. A 3D molecular gel structure derived by sol–gel method is provided as a precursor for vacuum freeze drying process. The typical inorganic precursor is an aqueous colloid solution such as sol or suspension. The new type of precursor results in a new columnar pore structure. The porous system keeps their high porosity even above 1500 °C in contrast with the reported heat resistance value (<800–1000 °C) of the porous alumina systems. The effects of the solvent content and other chemical additives as well as the drying conditions were studied on the porous structure. 3D SEM images represent the inner structure of porous materials.

Facile and green synthesis of (La0.95Eu0.05)2O2S red phosphors with sulfate-ion pillared layered hydroxides as a new type of precursor: controlled hydrothermal processing, phase evolution and photoluminescence

This study presents a facile and green route for the synthesis of (La0.95Eu0.05)2O2S red phosphors of controllable morphologies, with the sulfate-type layered hydroxides of Ln2(OH)4SO4·2H2O (Ln = La and Eu) as a new type of precursor. The technique takes advantage of the fact that the precursor has had the exact Ln:S molar ratio of the targeted phosphor, thus saving the hazardous sulfurization reagents indispensable to traditional synthesis. Controlled hydrothermal processing at 120 °C yielded phase-pure Ln2(OH)4SO4·2H2O crystallites in the form of either nanoplates or microprisms, which can both be converted into Ln2O2S phosphor via a Ln2O2SO4 intermediate upon annealing in flowing H2 at a minimum temperature of ∼ 700 °C. The nanoplates collapse into relatively rounded Ln2O2S particles while the microprisms retain well their initial morphologies at 1 200 °C, thus yielding two types of red phosphors. Photoluminescence excitation (PLE) studies found two distinct charge transfer (CT) excitation bands of O2− → Eu3+ at ∼ 270 nm and S2− → Eu3+ at ∼ 340 nm for the Ln2O2S phosphors, with the latter being stronger and both significantly stronger than the intrinsic intra-f transitions of Eu3+. The two types of phosphors share high similarities in the positions of PLE/PL (photoluminescence) bands and both show the strongest red emission at 627 nm (5D0 → 7F2 transition of Eu3+) under S2− → Eu3+ CT excitation at 340 nm. The PLE/PL intensities show clear dependence on particle morphology and calcination temperature, which were investigated in detail. Fluorescence decay analysis reveals that the 627 nm red emission has a lifetime of ∼ 0.5 ms for both types of the phosphors.

Micelle-Templated Oxides and Carbonates of Zinc, Cobalt, and Aluminum and a Generalized Strategy for Their Synthesis

Catalysis, energy storage, and light harvesting require functional materials with tailored porosity and nanostructure. However, common synthesis methods that employ polymer micelles as structure-directing agents fail for zinc oxide, for cobalt oxide, and for metal carbonates in general. We report the synthesis of the oxides and carbonates of zinc, cobalt, and aluminum with micelle-templated structure. The synthesis relies on poly(ethylene oxide)-block-poly(butadiene)-block-poly(ethylene oxide) triblock copolymers and a new type of precursor formed by chemical complexation of a metal nitrate with citric acid. A general synthesis mechanism is deduced. Mechanistic insights allow for the prediction of optimal processing conditions for different oxides and carbonates based on simple thermogravimetric analysis. Employing this synthesis, films of ZnO and Co3O4 with micelle-controlled mesoporosity become accessible for the first time. It is the only soft-templating method reported so far that also yields mesoporo...

A novel precursor system and its application to produce tin doped indium oxide

A new type of precursor has been developed by molecular design and synthesised to produce tin doped indium oxide (ITO). The precursor consists of a newly developed bimetallic indium tin alkoxide, Me(2)In(O(t)Bu)(3)Sn (Me = CH(3), O(t)Bu = OC(CH(3))(3)), which is in equilibrium with an excess of Me(2)In(O(t)Bu). This quasi single-source precursor is applied in a sol-gel process to produce powders and coatings of ITO using a one-step heat treatment process under an inert atmosphere. The main advantage of this system is the simple heat treatment that leads to the disproportionation of the bivalent Sn(II) precursor into Sn(IV) and metallic tin, resulting in an overall reduced state of the metal in the final tin doped indium oxide (ITO) material, hence avoiding the usually necessary reduction step. Solid state (119)Sn-NMR measurements of powder samples confirm the appearance of Sn(II) in an amorphous gel state and of metallic tin after annealing under nitrogen. The corresponding preparation of ITO coatings by spin coating on glass leads to transparent conductive layers with a high transmittance of visible light and a low electrical resistivity without the necessity of a reduction step.

A detailed view on the polycondensation of ionic liquid monomers towards nitrogen doped carbon materials

Recent works have shown the potential of special ionic liquids as a new type of precursor for nitrogen doped carbon materials. The combination of liquid state and negligible vapour pressure represents almost ideal precursor properties, simplifying the processing drastically as compared to solid and especially gas phase educts. Here, we delineate that the ionic liquids need to fulfil certain structural requirements for this purpose: while the cation must be nitrogen containing, e.g. pyridinium or imidazolium, reactive cyano functionalities in the anion are highly beneficial, such as in dicyanamide or tricyanomethide anions. Thermolysis of these precursors in an inert gas atmosphere leads to the formation of nitrogen doped carbon materials with a nitrogen content of about 10 m%, a turbostratic structure and very favourable electric and electrochemical properties. This paper will give an insight into the formation mechanism, structure determination and perspectives on applications of the final material.

Relationship of BRAF mutation, morphology, and apoptosis in early colorectal cancer

Many investigators have reported flat and depressed lesions as a new type of precursor of colorectal cancer. In our previous study, we determined that mutations in the BRAF gene may contribute to colorectal carcinogenesis by inhibiting apoptosis. However, the relationship among BRAF mutations, morphology and apoptosis in early colorectal cancer has not been clear. Therefore, gene alternation, morphology, and apoptosis in early colorectal cancer were investigated. Forty-five flat and depressed early colorectal cancer samples and 43 polypoid early colorectal cancer samples were analyzed. Mutations in the BRAF gene and the K-ras gene were examined by direct sequence analysis, and proliferative activity and induction of apoptosis were evaluated using immunohistochemical examination. RESULTS FINDINGS: BRAF mutations were found in 5 (11.1%) of 45 flat and depressed early colorectal cancer samples. No BRAF alteration was found in polypoid early colorectal cancer samples. Mutations in the K-ras gene were detected in 13 (30.2%) of 43 polypoid early colorectal cancer samples. The rate of submucosal invasion of the samples with BRAF mutations was significantly higher than that of the samples with K-ras mutations (p<0.05). BRAF and K-ras mutations were independent factors that influenced morphology in early colorectal cancer. In this study, the relationship between BRAF mutation and apoptosis is not so clear, but BRAF mutations and inhibition in apoptosis may play an important role in the developmental process of flat and depressed early colorectal cancer.

A new type of precursor for fibers in the system Si–C

Ceramic fibers with compositions in the system Si–C have a great potential for high-temperature applications. In recent years, our efforts have been dedicated to the development of polymers consisting of polysilanes suitable to spin fibers and build up matrices for CMC as well. The polysilanes are synthesized via disproportionation of the so-called disilane fraction [Richter, R., Roewer, G., Böhme, U., Busch, K., Babonneau, F., Martin, H.-P. et al., Appl. Organomet. Chem., 1997, 11, 71 (and references cited therein)]. A further thermal treatment yields materials which are soluble in organic solvents, and these solutions can be dry-spun to give fibers which are subsequently pyrolyzed. Solubility and high ceramic yield make this precursor a promising candidate for matrix infiltrations, too. The chemistry and the adjustment of viscosity and solubility to the requirements of the fiber processing as well as the conversion of the dried fibers to pure SiC fibers by thermal treatment will be reported.

MOCVD of Aluminum Nitride Thin Films with a New Type of Single‐Source Precursor: AlCl3:tBuNH2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

MOCVD of Aluminum Nitride Thin Films with a New Type of Single-Source Precursor: AlCl3:tBuNH2

A new type of precursor, AlCl 3 : t BuNH 2 adduct, has been designed. The synthesis, preparation, and characterization of AlN thin films have been carried out. The AlCl 3 : t BuNH 2 adduct was a stable solid material with high vapor pressure (2.5 torr at 65 °C) which was purified by sublimation. The structure of the precursor was fully identified by an X-ray single crystal analysis, elemental analysis, and nuclear magnetic resonance (NMR). The CVD process was performed using hydrogen under atmospheric pressure as the carrier gas. The film was characterized by Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The quality of the film prepared from the precursor was excellent, with a preferential c-axis orientation, exceptionally low carbon contamination, and an ideal N/Al atomic ratio.

Characterization of Cu2ZnSnS4 Thin Films Prepared by Vapor Phase Sulfurization

Cu2ZnSnS4 (CZTS) thin films could be successfully formed by vapor phase sulfurization of electron-beam-evaporated precursors on a soda-lime glass substrate. This film is an interesting material for absorber layer in a solar cell because all the constituents are readily available in the earth's crust. In this study, using a new type of precursors containing ZnS, we could achieve the strong adhesion of CZTS films to a glass substrate. From the result of scanning electron microscope (SEM) observation, it was confirmed that the surface morphology of CZTS films is much improved by using this new type of precursor. The X-ray diffraction pattern revealed that CZTS thin films have kesterite structures. From the measurement of transmittance and reflectance, the optical band-gap energy was estimated as 1.40–1.45 eV, which is very close to the optimum value for a solar-cell absorber. The highest open-circuit voltage of our cells based on CZTS films is 735 mV, which is a higher value than that reported in numerous other studies on CZTS.

New molecular compound precursor for aluminum chemical vapor deposition

A new type of precursor for aluminum chemical vapor deposition (Al-CVD) has been developed by mixing dimethylaluminum hydride (DMAH) and trimethylaluminum (TMA). The new precursor has proven itself to be effective for Al-CVD, where a good selectivity between the Si and the SiO 2 mask, a 3.0 μΩ cm resistivity and a pure Al film with low C and O contamination levels (under 100 ppm) were achieved. Quadrupole mass and infrared absorption analysis have shown that the precursor contains a new molecular compound, consisting of a DMAH monomer and a TMA monomer. The mixture has lower viscosity than DMAH and can be easily bubbled for a stable precursor vapor supply.

Monochromatic precursor starts

Whistler precursors are discrete emissions that precede two‐hop whistlers, starting shortly after the one‐hop delay. More evidence is presented that the precursor and associated whistler propagate through the same duct, and observations of a new type of precursor are presented. This new precursor has a monochromatic precursor start (MPS) which may or may not trigger a riser. Although MPS's may be emissions entrained by power line radiation (PLR), phase analysis of the starting frequencies shows that they are not simply related to harmonics of the power line frequencies in the two conjugate regions (50 Hz in New Zealand, 60 Hz in Alaska). If the MPS is due to entrainment by PLR, then previous theories of precursor generation need not be discarded. Forward triggering of a precursor at a power line harmonic by a hybrid whistler may occur.