Alain Mosset

Experimental evidence of structural evolution in ultrafine cobalt particles stabilized in different polymers—From a polytetrahedral arrangement to the hexagonal structure

Ultrafine cobalt particles have been reproducibly synthesized by decomposition of an organometallic precursor in the presence of a stabilizing polymer. The size of the stable monodisperse colloids thus obtained is seen to strongly depend on the nature of the polymer: around 4.2 nm diameter in polyphenylenoxide (PPO) and around 1.4 nm diameter in polyvinylpyrrolidone (PVP). Investigations by wide angle x-ray scattering (WAXS) and high-resolution transmission electron microscopy (HRTEM) give evidence for a size dependence of the structural organization, and hence for a close relationship between structure and synthesis conditions. Co/PPO particles exhibit a hexagonal compact structure with the metal–metal bond length of the bulk material while Co/PVP ones display an original structure. We show that the unusual features of the experimental data in Co/PVP clearly point to a nonperiodic polytetrahedral structure. Successful simulations of the HRTEM and WAXS results have been obtained using models built on the ...

New precursors in the chemistry of IVB transition metal alkoxides. V: Synthesis and molecular structure of Zr3Fe(μ4-O)(μ2-OC3H7)6-(OC3H7)4(acac)3

Abstract The reaction of iron(III) acetylacetonate with zirconium(IV) n-propanolate in n-propanol leads to a tetranuclear species Zr3FeO(OC3H7)10(acac)3. This compound crystallizes in the triclinic system (space group P 1 ): a = 12.426(2), b = 12.977(2), c = 20.129(4) A, α = 91.55(1), β = 97.90(1), γ = 100.53(1)°. The structure consists of discrete tetranuclear molecules. The metal atoms design an almost perfect tetrahedron around a four-fold coordinated oxygen atom. The zirconium atoms are in a seven-fold coordination and the iron atom in a five-fold coordination.

Crystal structure of M(IO3)2 metal iodates, twinned bypseudo-merohedry, with MII: MgII, MnII, CoII, NiII and ZnII

Abstract The non-centrosymmetric materials Zn(IO3)2, Mn(IO3)2, Co(IO3)2, Mg(IO3)2 and β-Ni(IO3)2 have been synthesised by evaporation of nitric acid solutions of metal salts and lithium iodate. All these compounds are isostructural and their structures were characterised both by X-ray diffraction on powder and single crystals. They crystallise in the monoclinic crystal system, space-group type P21 (no. 4) with a pseudo-hexagonal lattice, as shown by the lattice parameters of Mn(IO3)2 for example: a = 11.247(1) Å, b = 5.045(1) Å, c = 11.246(1) Å, β = 120.02(1)°, V = 552.5(1) Å3, Z = 4. This monoclinic symmetry with a ∼ c and β ∼ 120° leads to a three-individual pseudo-hexagonal twin by pseudo-merohedry. The structure reveals a three-dimensional network in which each octahedrally coordinated cation is linked to ten others via iodate bridges. All these metal iodates generate second harmonics.

Low-temperature process of the cubic lanthanidesesquisulfides:remarkable stabilization of theγ-Ce2S3 phasei

Upon treating the corresponding oxalates with carbon disulfide (p CS2 =130 Torr) at a heating rate of 5 °C min -1 , it is shown that the cubic γ-phase of pure rare-earth sesquisulfides (γ-Ln 2 S 3 ) can be obtained at 800 °C from samarium to holmium (also yttrium) and at 1000 °C from neodymium to dysprosium. By working on ternary sulfides Ce 2-x Ln x S 3 , it has been shown that the stabilization of the γ-phase occurs when the average ionic radius ranges between 1.015 and 1.104 A at 800 °C. However, the nature of the observed sulfide phase also depends greatly on the experimental conditions, i.e. the nature of the precursor and the heating rate. At 800 °C and 5 °C min -1 , cerium oxalate leads to the β-phase while cerium nitrate leads to the α-phase. On the other hand, with cerium oxalate, the lower the heating rate the higher the amount of cubic γ-phase obtained.

New precursors in the chemistry of IVB transition metal alkoxides II. Synthesis and molecular structure of Zr2Co4(μ6-O)(μ2-OC3H7)8(OC3H7)2(acetylacetone)4

The title compound crystallizes in the triclinic system (space group P1) with parameters: a=1206.9, b=1304.7, c=1335.0 pm, α=106.32, β=113.74, γ=102.66°; the final R value is equal to 0.047. The crystal structure determination reveals discrete hexanuclear molecules. The Zr 2 Co 4 O 19 inorganic core adopts a cubic close packing of oxygens, the metal atoms occupying octahedral holes. A μ 6 oxygen atom is located at the center of the metal octahedron.

Metal complexes of rubeanic acid. III: Large-angle X-ray scattering studies of amorphous copper(II) and nickel(II) complexes

Preparation et etude des deux complexes Cu(C 2 S 2 N 2 H 2 )(H 2 O) et Ni 4 (C 2 S 2 N 2 H 3 ) 2 (C 2 S 2 N 2 H 2 ) 3 (H 2 O) 0,25 . Les deux composes possedent essentiellement la meme structure locale

Polynuclear platinum complexes deriving from squaric acid

Abstract The squarate ion (C 4 O 4 ) 2− does not substitute for chlorine in K 2 [PtCl 4 ] or in (NH 3 ) 2 PtCl 2 but it reacts with the ‘ cis -dichlorodiammine hydrolysis products’ to yield two complexes. The first one ( 1 ) can be described from the results of an X-ray diffraction study as a tetranuclear chain of platinum atoms bridged by squaric anions. The second one ( II ) is an amorphous blue compound with the platinum atom in a formal oxidation state of 2.5. A structure involving dinuclear entities is proposed for II on the basis of XPS, EPR and LAXS analysis. Oxidation of I by nitric acid in the presence of X − (X − Cl − or Br − ) generates products IV and V involving an oxidation of 3.0 for platinum. Considering the whole set of complexes derived from squaric acid points to significant similitudes with the ‘amide platinum blues’.

A new solution route to silicates. Part 4.—Subtnicronic zircon powders

Submicron-sized zircon powders have been prepared by an aqueous sol-gel process. The starting products were zirconium oxychloride or oxynitrate and a water-soluble silicate. The reaction took place at 120 °C in a PTFE-lined bomb under autogenous pressure or even at 100 °C in refluxing conditions. The resulting powder has been characterized by XRD, IR, EDAX, SEM, TEM and EXAFS. Under pseudo-hydrothermal conditions, zircon was prepared as spherical particles with a very narrow size distribution (mean size 0.6 µm). Crystallinity was improved by thermal curing resulting, at 1100 °C, in disk particles (diameter 0.35 µm; thickness 0.13 µm).

A new bimetallic complex of ethylenediaminetetraacetic acid : Ag[Cu(C10H13N2O8)(H2O)].H2O

The structure of silver aqua(hydrogen ethylenediaminetetraacetato)cuprate(II) monohydrate, Ag[Cu(C10H13N2O8)(H2O)].H2O, is described. This molecular compound is only the second complex of ethylenediaminetetraacetic acid (edta) with silver to be reported. It crystallizes as a three-dimensional network which can be described as stacking layers connected by Cu2+ ions.

New compounds in the chemistry of Group 4 transition-metal alkoxides. Part 4. Synthesis and molecular structures of two polymorphs of [Ti16O16(OEt)32] and refinement of the structure of [Ti7O4(OEt)20]

Two polymorphs of the condensed species [Ti16(µ4-O)4(µ3-O)8(µ-O)4(µ-OEt)16(OEt)16] have been obtained: a monoclinic form prepared in absolute ethanol and a tetragonal one obtained from 5% aqueous ethanol. The monoclinic form (compound 1) crystallizes in the space group C2/c with a= 23.392(7), b= 19.627(8), c= 24.130(14)A and β= 96.4(4)°. The tetragonal variety (compound 2) crystallizes in the space group P42/n with a= 14.642(2) and c= 25.972(7)A. Both structures have been solved by direct methods and refined to R= 0.078 for 5766 independent reflections (compound 1) and to R= 0.053 for 3130 independent reflections (compound 2). They are built from different packings of the same hexadecanuclear molecule. Both molecules show slight differences in the titanium–oxygen network and in the orientations of the ethoxy groups. The initial hydrolysis product of tetraethyltitanium(IV), [Ti7O4(OEt)20]3 has been obtained by a new route. Its structure has been solved by direct methods and refined to R= 0.069 for 6293 independent reflections. This redetermination resulted in location of all the ethyl groups.