Abdessadek Lachgar

A comparative study of solid carbon acid catalysts for the esterification of free fatty acids for biodiesel production. Evidence for the leaching of colloidal carbon.

The preparation of a variety of sulfonated carbons and their use in the esterification of oleic acid is reported. All sulfonated materials show some loss in activity associated with the leaching of active sites. Exhaustive leaching shows that a finite amount of activity is lost from the carbons in the form of colloids. Fully leached catalysts show no loss in activity upon recycling. The best catalysts; 1, 3, and 6; show initial TOFs of 0.07 s(-1), 0.05 s(-1), and 0.14 s(-1), respectively. These compare favorably with literature values. Significantly, the leachate solutions obtained from catalysts 1, 3, and 6, also show excellent esterification activity. The results of TEM and catalyst poisoning experiments on the leachate solutions associate the catalytic activity of these solutions with carbon colloids. This mechanism for leaching active sites from sulfonated carbons is previously unrecognized.

Characterization and crystal structures of some fluorinated imides

Abstract The previously known, but not well-characterized, fluorinated imides, trifluoroacetyltrifluoroacetimide, HN(C(O)CF3)2 (1), acetyltrifluoroacetimide, HN(C(O)CH3)C(O)CF3 (2), and dichlorophosphoryltrifluoroacetimide, HN(P(O)Cl2)C(O)CF3 (3), have been shown to be moderately strong acids in aqueous solution; the first two compounds have pKa’s of 2.0 and 2.1 while the last compound consumes three equivalents of base per mole of imide owing to the hydrolyzable chlorine atoms. All three imides show a window of electrochemical inactivity on platinum from 0 to near +2.0 V. On vitreous carbon, (1) and (2) are inactive from –1.0 to +1.5 V and (3) from –1.0 to +1.0 V (vs. SCE). (1) crystallizes in a body-centered tetragonal unit cell while (2) and (3) crystallize in monoclinic unit cells. Hydrogen-bonded chains are formed in (1) and (2) and hydrogen-bonded dimers are formed in (3). The compounds were further characterized by 1H, 19F, and 13C NMR, FTIR, and elemental analysis.

High resolution solid state 31P NMR in some antimony-phosphates

Abstract Six antimony-phosphates have been studied by MAS high resolution solid state 31 P NMR. Correlations have been drawn between NMR chemical shifts and structural data. They show that the 31 P resonance line moves towards high field when the number of bridging oxygens in the PO 4 , group increases. The chemical shift anisotropy is related to the dimensionality of the solid network. It is smaller for 3D lattices. Water intercalation in layered phosphates leads to a shift of the 31 P resonance towards high or low field suggesting that protonation of some (PO 4 ) 3− group occurs. A correlation between the P-O π bonding and the chemical shift is also proposed.

Ti2Nb6Cl14O4: A Unique 2D–1D Network Combination in Niobium Cluster Chemistry

Layers of niobium clusters that are linked to each other through zigzag chains of edge-sharing [TiCl4 O2 ] ocatahedra are the central structural features of the title compound. Bridging of the chains by [(Nb6 Cl8i O4i )Cl6a ]6- clusters results in the formation of empty tunnels (a section of the structure is shown on the right).

A new iron oxophosphate SrFe3(PO4)3O with chain-like structure

A new strontium iron oxophosphate SrFe3(PO4)3O was synthesized by the solid state method and its structure was studied by single-crystal X-ray and electron diffraction, high-resolution electron microscopy, Mossbauer and IR spectroscopy. The compound crystallizes in a monoclinic system (space group P21/m) with unit-cell parameters: a = 7.5395(7), b = 6.3476(7) c = 10.3161(13) A ˚ , b = 99.740(9)1. The structure of SrFe3(PO4)3O represents a new structural type and is made up of isolated PO4 tetrahedra and FeOn polyhedra connected via common vertices and edges to form a 3D framework. Iron cations occupy three crystallographically independent sites with different oxygen environment: Fe1 and Fe2 occupy two octahedral sites, and Fe3 is five-coordinated. Two particularities of this structure are remarkably mentioned: the isolated {FeO6}n octahedral chains along the b direction and the five coordinated environment for the Fe3 position. Mossbauer spectroscopy confirmed the presence of only high-spin Fe 3+ cations in two types of coordination environment. The IR-data show the presence of only PO 3� 4 groups.

Silicon sheets by redox assisted chemical exfoliation.

In this paper, we report the direct chemical synthesis of silicon sheets in gram-scale quantities by chemical exfoliation of pre-processed calcium disilicide (CaSi2). We have used a combination of x-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive x-ray spectroscopy to characterize the obtained silicon sheets. We found that the clean and crystalline silicon sheets show a two-dimensional hexagonal graphitic structure.

Synthesis and crystal structure of indium arsenate and phosphate dihydrates with variscite and metavariscite structure types

The hydrothermal synthesis, crystal structure analysis, and spectroscopic studies of InPO4·2H2O (1) and InAsO4·2H2O (2) are reported. Compound 1 is isomorphic with metavariscite: monoclinic P21/n (No. 14), a = 5.4551(3) Å, b = 10.2293(4) Å, c = 8.8861(3) Å, β = 91.489(4)°, Z = 4, and compound 2 is isomorphic with variscite: orthorhombic Pbca (No. 61), a = 10.478(1) Å, b = 9.0998(8) Å, c = 10.345(1) Å, Z = 8. Their three-dimensional frameworks are built of corner sharing InO4(H2O)2 octahedra and MO4 (M = P5+ or As5+) tetrahedra. The water molecules in both compounds have different environments and are involved in different types of hydrogen bonding. Infrared spectroscopy indicates that water molecules are true H2O species.

Self-assembly and solvent-mediated structural transformation of one-dimensional cluster-based coordination polymer

Reactions between [Nb6Cl12(CN)6]4− and [Mn(salen)]+ in MeOH–H2O solvent mixture led to the formation of a new compound: {[(Mn2(salen)2)][[Mn(salen)(H2O)]0.67[Mn(salen)(MeOH)]1.33(Nb6Cl12(CN)6)]}·1.7H2O·2MeOH (1). Single crystal X-ray analysis has shown that 1 possesses 1D framework built of heterotrimeric supramolecular anions, {[Mn(salen)(s)]2[Nb6Cl12(CN)6]}2− and [Mn2(salen)2]2+ phenoxo bridged dimers linked to each other through two cyanide ligands located in axial positions. When 1 was left in a methanolic solution of (Me4N)+, its 1D framework was transformed into a 2D framework of the previously reported compound [Me4N]2[(Mn(salen))2(Nb6Cl12(CN)6))] (2) which has a 2D anionic 4,4-network built of [Nb6Cl12(CN)6]4− and [Mn(salen)]+ nodes linked by CN ligands (Zhou, Day and Lachgar, Chem. Mater., 2004, 16, 4870).1Magnetic susceptibility measurements indicate that 1 exhibits weak antiferromagnetic interactions due to the phenolate-bridged out-of-plane Mn(III) dimers with J = −1.50(5) cm−1. Thermal stability of 1 was studied.

Struktur und elektrochemische Untersuchung von Nb3Cl8

Nb3Cl8 wurde durch Reaktion von NbCl5 mit Niob-Metallpulver in einer geschlossenen Quarzglasampulle bei 700 °C dargestellt. Aus einer LiCl-Schmelze isolierte Einkristalle wurden fur die Strukturbestimmung mit einem IPDS-Rontgendiffraktometer (Raumgruppe P 3 m1, Z = 2, Gitterkonstanten a = b = 672,95(7) pm, c = 1223,2(2) pm (bei 100 K), R1 = 0,029, wR2 = 0,064 fur alle unabhangigen Reflexe) und die Messung des elektrischen Widerstandes ausgewahlt. Die Lithium-Einlagerung in die Struktur von Nb3Cl8 wurde elektrochemisch untersucht. Structure and Electrochemical Study of Nb3Cl8 The compound Nb3Cl8 was synthesized from NbCl5 and niobium metal in a sealed quartz ampoule at 700 °C. Single crystals, obtained from LiCl melt were used for X-ray structure determination (space group P 3 m1, Z = 2, lattice parameters a = b = 672.95(7) pm, c = 1223.2(2) pm (at 100 K), R1 = 0.029, wR2 = 0.064 for all independent reflections). Electrical resistivity measurements are reported. Electrochemical intercalation of lithium into the structure of Nb3Cl8 was studied.

Octahedral metal clusters as building units in a neutral layered honeycomb network, [Zn(en)]2[Nb6Cl12(CN)6]

A polymeric hybrid cluster-based compound with a double-layered honeycomb framework built of octahedral niobium cyanochloride clusters and [Zn(en)]2+ metal complexes was designed and synthesized at room temperature, and structurally characterized by single crystal X-ray diffraction.