Hydration of terminal alkynes on Nafion film in supercritical carbon dioxide

To find out the conditions for mild hydration of carbon–carbon triple bonds the hydration reactions of some terminal alkynes (FcCCH, PhCCH, C₅H₁₁CCH) on the Nafion film in supercritical carbon dioxide (sc-CO₂) were studied. The corresponding ketones were prepared in excellent yields. The hydration of 1-heptyne is accompanied by the isomerization of the terminal carbon–carbon triple bond into the internal one under acidic heterogeneous catalysis.     

The effect of density functional and dispersion interaction on structure and bonding analysis of uranium(VI) nitride complex [NU{N(CH2CH2NSiMe3)3}]: A theoretical study

Geometry and bonding energy analysis of uranium(VI) nitride complex [NU{N(CH₂CH₂NSiMe₃)₃}] were investigated with the DFT, DFT-D3 and DFT-D3(BJ) methods using density functionals (BLYP, BP86, PW91, PBE, revPBE and TPSS). The BLYP functional yields a UN bond distance of 1.788 Å for the model complex [NU{N(CH₂CH₂NSiMe₃)₃}] which is in close agreement with the experimental value of the UN bond distance of 1.799(7) Å for [NU{N(CH₂CH₂NSiⁱPr₃)₃}]. The calculated Mayer bond order (2.95) and Gopinathan–Jug bond order (3.18) indicate that the UN bond in this complex is essentially UN triple bonds. The electrostatic interaction is significantly smaller than the covalent bonding. The bond dissociation energy (BDE) is largest for the functional PBE and smallest for the functional TPSS. The DFT-D3 dispersion corrections are 5.3 kcal/mol (BLYP) and 5.0 kcal/mol (TPSS).     

Luminescent Au3Ag6 heterononanuclear complex of 1-ethynylcyclopentanol

Reaction of polymeric species (AgCCC₅H₈OH)_n(HCCC₅H₈OH = 1-ethynylcyclopentanol) with binuclear precursor [Au₂(μ-dppm)₂](PF₆)₂ (dppm = bis(diphenylphospnino)methane) caused isolation of Au₃Ag₆ heterononanuclear complex [Au₃Ag₆(μ-dppm)₃(μ₃– η¹-CCC₅H₈OH)₆](PF₆)₃. The Au₃Ag₆ (μ₃-CCC₅H₈OH)₆ skeleton exhibits a hexagonal prismatic structure formed by μ₃–η¹-CCC₅H₈OH bound to the Au₃Ag₆ cluster core. The compound is luminescent in both solid state and dichloromethane at both 298 and 77 K with the room temperature lifetimes in microsecond ranges, suggesting an emissive triplet parentage.     

A first mixed heteropentametallic transition metal complex: Synthesis and characterisation

The synthesis and characterisation of a novel [(η²-dppf)(η⁵-C₅H₅)Ru(CC)-1,4-(C₆H₄)PPh₂–Au–CC-bipy({[Ti](μ-σ,π-CCSiMe₃)₂}Cu)]PF₆ (dppf = 1,1′-bis(diphenylphosphino)ferrocene) is reported in which five different transition metals (Fe–Ru–Au–Cu–Ti) are linked by carbon-rich organic bridging units.     

The effect of Mg(OH)2 on furfural oxidation with H2O2

The oxidation of furfural in H₂O₂ and H₂O₂–Mg(OH)₂ system were systematically investigated and a rational explanation for the reaction mechanism was proposed. 2-formyloxyfuran, from selective oxidation of HCO group in furfural, was a crucial intermediate. The addition of Mg(OH)₂ suppressed the oxidation of furan ring of furfural and enhanced selectivities of 2(5H)-furanone (44.8%) and succinic acid (38.0%). FT-IR, Gaussian calculation and experimental results indicated that the process of furfural oxidation with H₂O₂ is homogeneous, and the synergy between dissolved Mg^2 + cations and OH⁻ ions facilitates the HOO⁻ attacking the carbon atom of HCO other than the CC bound of furan ring.     

Unsymmetrical cyrhetrenyl and ferrocenyl azines derived from 5-nitrofurane: Synthesis,structural characterization and electrochemistry

A new series of unsymmetrical cyrhetrenyl and ferrocenyl azines that were monosubstituted [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)]M {with MRe(CO)₃ and RH (1a) or RMe (1b); MFe(η⁵-C₅H₅) and RH (2a) or RMe (2b)} and disubstituted [Fe{(η⁵-C₅H₄)–C(Me)N–NCH(5-NO₂–2-C₄H₂O)}₂] (3a) were prepared by condensation reactions of the corresponding organometallic hydrazone [(η⁵-C₅H₄)–C(R)N–NH₂)]M with 5-nitro-2-furaldehyde. The ¹H and ¹³C{¹H} NMR spectra indicated that these compounds adopted an (E,E)-configuration about the ˃CN − bond and an s-trans conformation about the N1–N2 bond, and this result was confirmed by X-ray crystallographic analyses of 1a and 2b. The opposite electronic effects of the organometallic fragments correlate with the co-planarity of the [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)] system, the reduction potential of the nitro group (E_1/2) and the chemical shifts of the iminic carbons.     

Preparation of high-temperature stable SiBCN fibers from tailored single source polyborosilazanes

Bulk SiBCN ceramics derived from polyborosilazanes of the type [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H; C₂H₄ = CHCH₃, CH₂CH₂) exhibit an exceptional structural stability at high temperature. Therefore, such quaternary systems are of great scientific and technical interest as fibrous reinforcements intended for high-temperature applications. In this context, the design of novel polyborosilazanes, which display properties tailored for the preparation of SiBCN fibers, is studied. Boron-modified polysilazanes of the type [B(C₂H₄SiRNCH₃)₃]_n (1b, R = CH₃; 2b, R = H) are prepared via aminolysis of the tris(dichlorosilylethyl)boranes B(C₂H₄SiRCl₂)₃ (1, R = CH₃; 2, R = H). It is shown that the functionalisation of the precursors with NCH₃ units improves their processability (i.e. solubility) compared to that of their ammonolysed analogs [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H). In addition to the influence of the NCH₃ units, the presence of the SiCH₃ functions in such polymers offers the best potential for the preparation of fibers by melt-spinning. As-spun fibers are then converted under controlled atmosphere into high-temperature stable SiBCN fibers according to the polymer-derived ceramic route.     

A model study for the breaking of cyanogen out of CNx within DFT

To explain the nitrogen low rate in CVD CN_x layers, and their amorphisation, a release of gaseous species containing N was proposed. Previous modelling studies based on local density functional theory use pyrite type CN₂ as starting model to assess the release of molecular nitrogen. This model is completed here to investigate another mechanism of release of cyanogen as another gaseous species. The theoretical pyrite-like C₂N wherein C and N atoms form dumbbells in octahedral sites of a carbon face-centred sub-lattice is proposed as likely to model it. It demonstrates a good compressibility (B₀ = 272 GPa) and a mechanical instability, which supports both release of atoms and the amorphisation of layers. However, the variation of interatomic distances under strain leads to propose the formation of a radical species CN. This is enforced by the consideration of the chemical bonding and its evolution in the model with the E_COV and ELF functions. The release of nitrogen in molecular cyanogen is consequently substituted by a mechanism which implies a CN radical species, which is likely to recombinate at the CVD layers surfaces.     

X-ray photoelectron spectroscopy characterization of CNx thin films deposited by electron beam evaporation and nitrogen ion bombardment

Carbon nitride thin films have been deposited on Si(100) substrates by electron beam evaporation of graphite and simultaneous low energy nitrogen ion bombardment. The layers were analyzed by X-ray photoelectron spectroscopy. The synthesized layers are tetrahedrally bonded and amorphous, consisting of sp³-coordinated carbon with one nitrogen atom between its nearest neighbors. About 27% of the nitrogen is in CN bonds and some nitrogen is in CN bonds.     

Hyperbranched polycarbosiloxanes and polycarbosilanes via bimolecular non-linear hydrosilylation polymerization

The syntheses and selected structure–property relationships of two series of polycarbosiloxanes (HB-PCSOX) and polycarbosilanes (HB-PCS) prepared by the platinum-catalyzed bimolecular non-linear hydrosilylation polymerizations of commercially available 1,3-diallyl- or 1,3-divinyl- disiloxanes or disilanes and tri- or tetra-functional siloxysilanes or silanes (i.e., A_x + B_y polymerization systems where x = 2 and y = 3 or 4) are described. The polymerizations were controlled to avoid gelation and ensure preparation of non-crosslinked soluble polymer products by adjusting the molar ratios of the reacting A (allylsilyl, Si–CH₂–CHCH₂, or vinylsilyl, Si–CHCH₂) and B (silyl, Si–H) reactive functional groups such that r ≤ 1/[(x ? 1)(y ? 1)] or r ≥ (x ? 1)(y ? 1) where r = [A]/[B]. The polymers were characterized by IR, ¹H, ¹³C and ²⁹Si NMR, SEC, DSC and TGA. Their molecular weights were found to increase in the following order of the side-group substitution in the 1,3-divinyldisiloxane monomer used: EtO > Me > MePh > Ph₂, consistent with the increased electron-donation to the vinyl groups causing their increased reactivity in hydrosilylation. These polymers represent unique yet easily and economically available multifunctional nanoscopic dendritic building blocks for more complex 3D nano-structured materials for a variety of applications in electronics, photonics, lithography, specialty coatings, etc.     

Synthesis and reactivity of an 2-azabutadiene-based π-conjugated dithioether: Formation of a N,S-ligated molybdenum chelate complex and C,N,S-pincer complexes of palladium and platinum

Nucleophilic attack of sodium isopropylthiolate on 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl₂CC(H)–NCPh₂}] (1) affords the 2-azabutadiene derivative [(i-PrS)₂CC(H)–NCPh₂] (2). Upon irradiation of Mo(CO)₆ in THF in the presence of 2, the chelate complex cis-[(OC)₄Mo{(i-PrS)₂CC(H)–NCPh₂}] (3) is obtained. Coordination on Mo occurs through the imine nitrogen and a thioether group. Polydentate dithioether 2 acts as N,C,S-pincer ligand after orthometallation reaction with Pd(II) or Pt(II). The molecular structures of 2 and (C,N,S)-[(i-PrS)₂CC(H)–NC(Ph)C₆H₄)PtCl] (4b) have been determined by X-ray diffraction studies.     

Hydrodenitrogenation of Simple Aromatic Amines on Molybdena Catalysts

The hydrotreatment of some aromatic amines was studied at temperatures ranging from 400 to 450°C and P_H2=1 atm under flow conditions. Hydrogenolysis of aromatic amines involves direct cleavage of the C(sp²)N bond without saturation of the aromatic ring. The presence of hydrogen sulphide in the reaction stream has a promotional effect on the hydrogenolysis of C(sp³)N bond and an inhibitive effect on the hydrogenolysis of C(sp²)N bond. The use of a saturated hydrocarbon as diluent facilitates CN bond hydrogenolysis in the presence of hydrogen, irrespective of the carbon being sp² or sp³ hybridized.     

Electrically conductive silicon carbide with the addition of TiNbC

The work deals with the preparation of dense SiC based ceramics with high electrical conductivity. SiC samples with different content of conductive TiNbSiCO based phase were hot pressed at 1820 °C for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of 50 wt% TiNbC (molar ratio of Ti/NbC is 1:1.8) and 50 wt% eutectic composition of Y₂O₃SiO₂. Composite with 30% of conductive TiNbSiCO phase showed the highest electrical conductivity 28.4 S mm^?1, while the good mechanical properties of SiC matrix were preserved (fracture toughness K_IC = 5.4 MPa m^1/2 and Vickers hardness 17.8 GPa).The obtained results show that the developed additive system is suitable for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.     

Structural relaxation of sputtered amorphous carbon nitride films during thermal annealing

A study of the stress relaxation caused by post-deposition thermal annealing of carbon nitride thin films (CN_x) deposited onto Si substrates has been carried out. The intrinsic stress values were correlated with Fourier transform spectrometer (FTIR) and thermal desorption mass spectroscopy (TDMS) results. FTIR spectra showed the existence of N–Csp³, NCsp² and C≡N triple bonds in the deposited films and indicates the occurrence of their porous character. The analysis of the spectra versus annealing temperature (T_A) reveals two rearrangement mechanisms of the microstructure. Up to 200 °C, the reversion of NCsp² to N–Csp³ and CCsp² respectively, and then an increase of the connectivity of the C–C network for higher T_A. These dissociation/recombination mechanisms are used to describe the stress release occurring within the (CN_x) films upon heating.     

Deposition of carbon nitride films using an electron cyclotron wave resonance plasma source

Hydrogenated amorphous carbon nitride (a-C:N:H) has been synthesised using a high plasma density electron cyclotron wave resonance (ECWR) technique using N₂ and C₂H₂ as source gases, at different ratios and a fixed ion energy (80 eV). The composition, structure and bonding state of the films were investigated and related to their optical and electrical properties. The nitrogen content in the film rises rapidly until the N₂/C₂H₂ gas ratio reaches 2 and then increases more gradually, while the deposition rate decreases steeply, placing an upper limit for the nitrogen incorporation at 30 at%. For nitrogen contents above 20 at%, the band gap and sp³-bonded carbon fraction decrease from 1.7 to 1.1 eV and ∼65 to 40%, respectively. The transition is due to the formation of polymeric CN, CN and NH groups, not an increase in CH bonds. Films with higher nitrogen content are less dense than the original hydrogenated tetrahedral amorphous carbon (ta-C:H) film but, because they have a relatively high band gap (1.1 eV), high resistivity (10⁹ Ω cm) and moderate sp³-bonded carbon fraction (40%), they should be classed as polymeric in nature.     

Dinuclear neodymium(III) complex of cationic {12[ane]HN4(CH2CCH)4}+ with sensitized near-infrared luminescence by ion-association sensitizer

A new complex Nd₂(hfac)₆(CH₃COO)₂ {12[ane]HN₄(CH₂CCH)₄}₂ (hexafluoroacetylacetonate, hfac) was synthesized and characterized. Upon excitation of the organic cation {12[ane]N₄H(CH₂CCH)₄}⁺ (protonation on one of the nitrogen atoms of N,N′,N′,N‴-tetra-(3-prop-1-yne)-1,4,7,10-tetrazacyclododecane), the neodymium NIR luminescence is sensitized through Förster energy transfer mechanism.     

Nonlinear optical properties in tetrametallic Fe3Mn complexes with pseudo-C3 symmetry

New type of 3D chromophores [{CpFeC₅H₄CRCH4-py}₃Mn(CO)₃]BF₄ (1) with weakly interaction subchromophore were synthesized and found to display improved nonlinearity compared with their 1D reference systems [(CpFeC₅H₄CRCH4-py)Mn(CO)₅]BF₄ (2).     

Infrared spectroscopy of some carbon-based materials relevant in combustion: Qualitative and quantitative analysis of hydrogen

A detailed procedure for the quantitative analysis of aromatic and aliphatic hydrogen based on infrared spectroscopy was set up and implemented on some carbon-based materials produced from organic precursors (naphthalene pitch) and/or relevant in combustion field (asphaltenes, carbon particulate matter, carbon black), spanning in the H/C atomic ratio range from 0.1 to 1. The quantitative FT-IR analysis involved the spectral deconvolution in the CH vibrations regions and the calibration factors of diverse standard species having spectral characteristics suitable for the detailed peak-to-peak analysis of the CH stretching (3100–2800 cm⁻¹) and aromatic CH bending (900–700 cm⁻¹) regions. The good agreement between the H/C atomic ratio obtained by quantitative FT-IR analysis and elemental analysis showed a reasonable reliability of the procedure. The major value of the developed FT-IR quantitative technique relies also on the capacity of discriminating between the different kinds of aliphatic and aromatic hydrogen. The quantitative and detailed analysis of hydrogen in form of CH₃, CH₂ and CH groups and in form of solo, duo and trio/quatro aromatic hydrogens showed to be useful also for inferring the structure of the aromatic moieties constituting the CC backbone of carbon materials.     

Synthesis and structural characterizations of organolanthanide complexes with amino-tethered guanidinate ligand (C5H5)2Ln[H2N(CH2)3NC(NHiPr) NiPr)] (Ln = Yb,Y, Er,Dy)

Reaction of N,N′-diisopropylcarbodiimide (ⁱPrNCNⁱPr) with H₂N(CH₂)₃NH₂ and (C₅H₅)₃Ln, give (C₅H₅)₂Ln[H₂N(CH₂)₃NC(NHⁱPr) NⁱPr)] in high yields, indicating that the N–H bonds of one NH₂ group readily add to the CN double bonds of carbodiimide and one cyclopentadienyl group is eliminated to construct a novel amino-tethered guanidinate anionic ligand [H₂N(CH₂)₃N C(NHⁱPr)NⁱPr)]⁻.