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Tris(pentafluorophenyl)borane catalyzed Si-H bond activation opens the door to numerous transition-metal-free reduction processes and is widely used in organic and polymer chemistry. However, chemical stability of B(C6F5)3 in the presence of silyl hydrides is limited, which can strongly affect its catalytic activity. Transformations of B(C6F5)3 in the presence of phenyldimethylsilane, triethylsilane and triethylgermane were studied by 19F NMR and UV spectroscopy, GC/MS and quantum-mechanical calculations. The observed exchange of pentafluorophenyl group attached to boron to hydrogen results in the formation of bis(pentafluorophenyl)borane, which has a strongly reduced ability to activate the Si-H bond. The substitution kinetics were studied by following the disappearance of absorption of the B(C6F5)3 charge transfer peak in the UV spectrum. Complementary quantum mechanical calculations allowed us to propose a mechanism of the ligand exchange reaction, which involves electrophilic substitution of the pentafluorophenyl group through a four-center transition state.

Knowledge and systematic research on the mechanical properties of amorphous materials in the transition temperature range from amorphous to crystalline is a fundamental scientific interest. Planning the use of these materials must be based on thermomechanical properties information. TiZrCuPd amorphous alloys belong to the potentially lead-free solders of relatively large glass forming ability. The paper presents results of the differential scanning calorimetry, thermomechanical, microstructural and phase analysis of the TiZrCuPd amorphous alloys containing 14 at% Pd and 2 and 3 at% Sn additions at the expenses of Cu content. The samples were investigated in the tensile-load modulated and dilatometric modes in the temperature range of the glass transition and crystallization. The relation between two steps of crystallization process, plastic flow and resulting ability for the deformation was analyzed and related to the microstructure and phase analysis. The determined temperature range of glass transition and primary crystallization show enhanced ductility in the dependence on the Sn additions and homogeneous deformation in this range. The engineering strain of alloys reveals its dependence on the temperature, especially visible in the sample for the 2 at% Sn additive.

The paper deals with TiO2-based thin films, doped with Cr and N, obtained by magnetron co-sputtering from titanium dioxide ceramic and chromium targets in Ar + N2 atmosphere. Co-doped samples of Ti(Cr)O2:N are investigated from the point of view of morphological, crystallographic, optical, and electrical properties. Characterization techniques such as: X-ray diffraction, XRD, scanning electron microscopy, SEM, atomic force microscopy, AFM, Energy Dispersive X-ray spectroscopy, EDX, X-ray photoelectron spectroscopy, XPS, optical spectrophotometry as well as impedance spectroscopy are applied. XRD reveals TiO2 and TiO2:N thin films are well crystallized as opposed to those of TiO2:Cr and Ti(Cr)O2:N. XPS spectra confirm that co-doping has been successfully performed with the biggest contribution from the lower binding energy component of N 1s peak at 396 eV. SEM analysis indicates uniform and dense morphology without columnar growth. Comparison between the band gaps indicates a significant shift of the absorption edge towards visible range from 3.69 eV in the case of non-stoichiometric Ti(Cr)O2−x:N to 2.78 eV in the case of stoichiometric Ti(Cr)O2:N which should be attributed to the incorporation of both dopants at substitutional positions in TiO2 lattice. Electrical conductivity of stoichiometric Ti(Cr)O2:N increases in comparison to co-doped nonstoichiometric TiO2−x thin film and reaches almost the same value as that of TiO2 stoichiometric film.

This work deals with TiO 2 nanopowders, the grain size of which was intentionally changed from about 10 nm to 30 nm by controlling the flow rate of the titanium organic precursor of C 16 H 28 O 6 Ti in flame spray synthesis (FSS). The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) compared with the results of Brunauer–Emmett–Teller (BET) nitrogen adsorption isotherms and X-ray diffraction (XRD) revealed non-agglomerated, spherical grains composed mostly of anatase. Annealing at 700 °C resulted in a partial phase transformation from anatase to rutile, with rutile crystallites as large as 57 nm. The formation of stoichiometric TiO 2 was confirmed by means of X-ray photoelectron spectroscopy. Electrical conductivity determined from dc and ac measurements increased upon reduction in grain size. The dynamic changes in the electrical resistance observed upon interaction with hydrogen over the range of 50–3000 ppm at a constant temperature chosen within the interval of 200 °C–400 °C, were reproducible. Theoretical model, based on the Schottky barriers formation at grain contacts, was applied to the sensor responses obtained in this work. Experimental data of the electrical conductivity in dry air were used to derive the temperature dependence of the band bending energy ( E O = 0.22–0.38 eV over the temperature range of 200–400 °C). The difference between the activation energy of water desorption and hydrogen atom adsorption (Δ E ) – the only fitting parameter of the adopted model – was found to decrease linearly with the specific surface area (SSA) of the TiO 2 nanomaterials.

Highlights: • Nanopowders of TiO{sub 2}:Cr with different amount of Cr dopant were obtained by flame spray synthesis, FSS. • Increase in the optical absorption and a shift of the absorption edge were observed upon Cr doping. • HERFD-XANES measurements indicated that the average valence state of titanium ions was preserved. • Increasing magnetic susceptibility of a paramagnetic character was observed upon Cr doping. - Abstract: The paper reports on the results of a study of optical, electronic and magnetic properties of TiO{sub 2} nanopowders doped with Cr ions. Diffused reflectance spectra reveal an increase in the optical absorption and a shift of the absorption edge towards lower energies upon Cr doping. Direct information on the Ti electronic state and the symmetry of its nearest environment is obtained from XANES Ti K-edge spectra. Magnetic behaviour is probed by means of the temperature dependence of DC magnetic susceptibility. Increasing magnetic susceptibility of a paramagnetic character is observed upon increasing chromium doping. The Curie constant of TiO{sub 2}:10 at.% Cr sample (0.12 emu K/mol Oe) is lower than that expected for Cr{sup 3+} (0.1875 emu K/mol Oe) possibly due to the appearance of Cr{sup 4+} or the presence of the orbital contributionmore » to the magnetic moment.« less

The aim of this work is to demonstrate that thermal modulation improves the selectivity of TiO2 –based resistive-type gas sensors. Sensor array, operating upon sinusoidal temperature profile over a temperature range of 240 – 300 °C, is comprised of nanocrystalline TiO 2 :Cr (0.1–10 at.% Cr) semiconductors switching from n-type to p-type at about 1 at.% Cr. Electrical resistance responses to reducing and oxidizing gases such as NO, NO 2 , H 2 , CH 4 , C 3 H 8 (0 – 3000 ppm) are dynamically recorded and compared in order to assess cross-sensitivity as well as humidity interference. Theoretical model developed for simple gas-solid interactions is extended to hydrogen.

Nanocomposites of TiO 2 /SnO 2 for hydrogen detection have been prepared by mechanical mixing of TiO 2 and SnO 2 nanopowders with different specific surface area SSA = 150.9 m 2 /g (TiO 2 ) and SSA = 18.3 m 2 /g (SnO 2 ). Nanocomposites consist of two distinct components: larger – grain (21–28 nm) cassiterite SnO 2 and smaller – grain (8–11 nm) rutile TiO 2 as indicated by X-ray diffraction measurements and transmission electron microscope, TEM, images. Nanopowders of 50 mol% TiO 2 /50 mol% SnO 2 are composed of small, elongated TiO 2 forms mixed with larger SnO 2 grains of regular shape as demonstrated by TEM. Scanning electron microscopy, SEM of gas sensing tablets, prepared by pressing nanopowders under 25 MPa at 400 °C reveal a high degree of agglomeration. Sensor responses in the electrical resistivity over a wide range of concentrations from 50 to 3000 ppm H 2 at a constant temperature chosen within the interval 250–400 °C have been measured and analyzed before and after sample conditioning at 500 °C in Ar + 7% H 2 atmosphere. Sensing tablets of 50 mol% TiO 2 /50 mol% SnO 2 display the highest sensitivity to hydrogen at moderate temperatures of 250–300 °C. Kinetics of the sensor responses are improved and the recovery time is significantly reduced as a result of annealing in the reducing atmosphere.

The synthesis and X-ray structure determination of an uncommon ionic aluminum bisphenoxide [Al(THF)4(Cl)2]+[Al(mcmip)2]−·1.1 THF (1) and its neutral analogue (mcmip)Al(CH2CH3)(THF) (2) are reported (mcmipH2: 2,2′-methylenebis(4-chloro-3-methyl-6-(isopropyl)phenol). The ligand was reacted in THF with diethyl aluminum chloride, respectively triethyl aluminum, under liberation of ethane to yield crystalline aluminum bisphenoxides. Compound 2 exhibits the usual structural features found in neutral THF-aluminum bisphenoxides adducts whereas the ionic compound 1 consists of a cationic octahedral aluminum dichloride moiety, [Al(THF)4(Cl)2], and an anionic di-bisphenoxide aluminate fragment [Al(mcmip)2] containing two 2,2′-methylenebis(4-chloro-3-methyl-6-(isopropyl)phenol) ligands. Both aluminum bisphenoxides were tested as catalysts in the copolymerization of cyclohexene oxide with CO2 and displayed similar good catalytic activities although the carbonate amounts present in the copolymer remain low.

Nanocrystalline powders of TiO2 and TiO2:Cr (0.1–10 at.% Cr) obtained by flame spray synthesis (FSS), are used as starting materials for preparation of gas sensors. Characterization of nanopowders is carried out by thermogravimetry (TG), Brunauer–Emmett–Teller (BET), adsorption isotherms, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Gas sensing materials are calcined at 400 °C in a form of tablets, the morphology of which is similar to that of starting materials. The mass loss of nanopowders upon heating, as determined from its temperature profile in TG, is correlated with the specific surface area (SSA) obtained from BET measurements. High SSA exceeding 100 m2/g is inherently related to the enhanced decomposition of organic residua below 400 °C. XRD diffraction patterns indicate small crystallite sizes (6–27 nm) and the presence of both polymorphic forms: anatase and rutile, independently of the form of nanomaterials. SEM images demonstrate agglomeration of crystallites into spherical grains. Gas sensing characteristics of TiO2:Cr nanosensors upon interaction with H2 are recorded in a self-assembled experimental system. Detection of hydrogen is carried out over the concentration range of 50–3000 ppm at the temperatures extending from 200 to 400 °C. It is demonstrated that nanomaterials based on TiO2:Cr are attractive for ultimate sensor applications due to a substantial decrease in the operating temperature down to 210–250 °C. At a certain level of doping (of about 5 at.%) a reversal of the sensor response from that of n-type to that of p-type semiconductor is seen. This effect can be accounted for by the acceptor-type substitutional defects C r ′ Ti built into TiO2 lattice.

The synthesis, spectroscopic characterisation and X-ray structure determination of the first aluminium para -chloro-bisphenoxides [Al 2 (mbpcp) 2 (C 2 H 5 ) 2 (THF) 2 ] and [Al 3 (mbpcp) 2 (C 2 H 5 ) 5 ] (mbpcp = 2,2′-methylenebis(4-chlorophenol) are reported. 2,2′-Methylenebis(4-chlorophenol) was reacted with triethyl aluminium to yield under liberation of ethane, aluminium para -chloro-2,2′-methylene-bisphenoxides with different molecular complexities: a dinuclear and a trinuclear specie, both displaying two bridging bisphenoxide ligands. The nature of the solvent (coordinating or not) influences the aggregation degree of the final product. The use of a coordinating solvent like THF yields a dimeric structure with a bisphenol:metal ratio of 1 to 1 which displays a trigonal-bipyramidal coordination geometry around the aluminium atoms whereas using an apolar, weak-coordinating solvent like diethyl ether yields a trinuclear species with a bisphenol:metal ratio of 2 to 3, displaying aluminium atoms with both tetrahedral and trigonal-bipyramidal coordination geometries. These compounds were tested in preliminary screening tests as catalysts of the homopolymerisation of cyclohexene oxide (CHO) and copolymerisation of CHO with carbon dioxide. Both aluminium bisphenoxides are highly active in the ring opening polymerisation of CHO (RT, reaction time M n ranging from 31 000 to 40 700 g/mol, polydispersities from 1.2 to 1.4). Both compound are also active in the copolymerisation of CHO with CO 2 although the carbonate amount remains low (75 bar, 90 °C, reaction time 8 h, M n ranging from 6800 to 15 200 g/mol, polydispersities from 1.9 to 2.5).

Reacting triethyl aluminum and diethyl aluminum chloride with the chelating bisphenol ligands mdtbpH2 and mmcpH2 [mmcpH2: 2,2′-methylenebis(4-methyl-6-(1-methyl-cyclohexyl)phenol); mdtbpH2: 2,2′-methylenebis(4,6-di-tert-butyl-phenol)] afforded monomeric and dimeric aluminum bisphenoxides with reactive Al–Cl and Al–C2H5 moieties. We present here the X-ray structure determination of some of the isolated compounds as well as the preliminary catalytic tests in copolymerization reactions with cyclohexene oxide and carbon dioxide.