Christiane Perrin

Red‐NIR Luminescent Hybrid Poly(methyl methacrylate) Containing Covalently Linked Octahedral Rhenium Metallic Clusters

The embedding of functional inorganic entities into polymer matrices has become an intense field of investigation in which the main challenges are to keep the added value of the inorganic entities while preventing their self-aggregation within the organic matrix. We present a simple way to obtain a homogeneous highly red-NIR luminescent hybrid copolymer that contains covalently bonded nanometric-sized {Re(6)} octahedral clusters. The [Re(6)Se(i)(8)(OH)(a)(6)](4-) cluster complexes are primarily functionalized in two steps with tert-butylpyridine (TBP) and methacrylic acid (MAC) to give neutral [Re(6)Se(8)(TBP)(4)(MAC)(2)] building blocks that are copolymerized with methyl methacrylate (MMA) either in solution or in bulk in the presence of azobisisobutyronitrile as an initiator. Several samples containing 0, 0.025, 0.05, and 0.1 wt % of functionalized {Re(6)} clusters were prepared. As the {Re(6)} cluster/MMA ratio is very low, the obtained copolymers keep the entire processability of pure poly(methyl methacrylate) (PMMA), as demonstrated by differential scanning calorimetry and thermogravimetric analysis. Voltammetric and luminescence studies also indicate that the intrinsic properties of the clusters are preserved within the polymer matrix. All the samples show a bright (emission quantum yield=0.07), broad, and structureless emission band, which extends from lambda=600 nm to more than lambda=950 nm, with the maximum wavelength centered around lambda(em)=710 nm either in solution or in the solid state. Moreover, the high stability of the incorporated inorganic phosphors prevents the material from photobleaching, and thus the luminescence properties are kept entirely even after nine months of ageing.

Silver Molybdate and Silver Tungstate Nanocomposites with Enhanced Photoluminescence

Silver molybdate (Ag2MoO4) and silver tungstate (Ag2WO4) nanomaterials were prepared using two complementary methods, microwave assisted hydrothermal synthesis (MAH) (pH 7, 140 °C) and co-precipitation (pH 4, 70 °C), and were then used to prepare two core/shell composites, namely α-Ag2WO4/β-Ag2MoO4 (MAH, pH 4, 140 °C) and β-Ag2MoO4/β-Ag2WO4 (co-precipitation, pH 4, 70 °C). The shape and size of the microcrystals were observed by field emission scanning electron microscopy (FE-SEM), different morphologies such as balls and nanorods. These powders were characterized by X-ray powder diffraction and UV-vis (diffuse reflectance and photoluminescence). X-ray diffraction patterns showed that the Ag2MoO4 samples obtained by the two methods were single-phased and belonged to the β-Ag2MoO4 structure (spinel type). In contrast, the Ag2WO4 obtained in the two syntheses were structurally different: MAH exhibited the well-known tetrameric stable structure β-Ag2WO4, while co-precipitation afforded the metastable β-Ag2WO4 allotrope, coexisting with a weak amount of the α;-phase. The optical gap of β-Ag2WO4 (3.3 eV) was evaluated for the first time. In contrast to β-Ag2MoO4/β-Ag2WO4, the α-Ag2WO4/β-Ag2MoO4 exhibited strongly-enhanced photoluminescence in the low-energy band (650 nm), tentatively explained by the creation of a large density of local defects (distortions) at the core-shell interface, due to the presence of two different types of MOx polyhedra in the two structures.

One-pot synthesis and characterizations of bi-functional phosphor–magnetic @SiO2nanoparticles: controlled and structured association of Mo6 cluster units and γ-Fe2O3nanocrystals

Nanostructured silica coated bifunctional nanoparticles based on [Mo(6)Br(14)](2-) units as phosphorescent dye and magnetic gamma-Fe(2)O(3) nanocrystals were synthesized and characterized.

Structure and magnetic properties of two niobium chlorides with ¦Nb6Cl12¦n+ (n = 2, 3) units: KLuNb6Cl18 and LuNb6Cl18

Abstract The quaternary chloride KLuNb6Cl18 and the ternary chloride LuNb6Cl18 were synthesized. They crystallize in the rhombohedral lattice R 3 and exhibit ¦Nb6Cl12¦2+ and ¦Nb6Cl12¦3+ units respectively. In the first case, the ¦Nb6Cl12¦2+ unit has 16 e− per Nb6 and the cluster is non-magnetic; in the second case, the ¦Nb6Cl12¦3+ unit has 15 e− per Nb6 and the cluster is paramagnetic owing to one unpaired electron. We present here the synthesis of these compounds, the structural results and the magnetic properties which depend on the variation in the oxidation state of the cluster.

Recent investigations on the (Me6L18)n unit based halides and oxyhalides (Me Nb, Ta and L Cl, Br, O) with rare earths as countercations: Electronic and steric effects

Abstract In this paper are reviewed a number of recently obtained (Me 6 L 18 ) n− based halides and oxyhalides with rare earths as countercations: M x REMe 6 X 18 (KLuNb 6 Cl 18 type, R 3 , and CsLuNb 6 Cl 18 type, P 3 1c) and REMe 6 X 13 O 3 (ScNb 6 Cl 13 O 3 type, 14 1 22). Their crystal structure data, obtained from isotypic compounds with judiciously chosen MREMeX combinations, have allowed us to discuss rigorously the most important structural features appearing commonly in the Me 6 cluster chemistry: the systematic evolution of the MeMe intracluster and the Meligand distances, depending on both electronic and steric effects. The influence of countercation size on the (Me 6 L 18 ) n− stacking is also considered. All these results form the basis of a consistent understanding of the (Me 6 L 18 ) n− based chemistry, when substitutions are performed on the various elements constituting these compounds.

Nouveaux thiochlorures de molybdène(II): Mo6Cl10Y (Y = S, Se, Te): Structure et propriétés magnétiques et électriques

Abstract The thiochlorides Mo6Cl10Y (Y = S, Se, Te) have been prepared; they are isostructural with Nb6I11, space group Pccn, and have four formula units per unit cell. The X-ray structure of Mo6Cl10Se has been determined from three-dimensional single-crystal counter data and refined to a final R value of 0.053 for 3350 independent reflections. The most important result concerning this structure is a statistical distribution of the Se atom on the unit (Mo6X′8) with X′ ⋍ 7 8 Cl + 1 8 Se : so the compound Mo6Cl10Se must be formulated (Mo 6 Cl 7 Se)Cl 4 2 Cl 2 2 . The diamagnetic and dielectric behavior of these new thiochlorides is discussed.

Fluorination of YBa2Cu3O6.7 : Powder neutron diffraction determination of fluorine sites and their influence on the superconducting properties

Abstract The crystal structures of YBa2Cu3O6.7 before and after 30 minutes or 75 minutes of fluorination under diluted NF3 at 300°C, were determined by powder neutron diffraction experiments. For short time of fluorination, the occupancy of the (0, 1 2 8:48 AM 6/6/02, 0) site increases while the one of the ( 1 2 , 0, 0) position does not vary too much. For higher fluorine concentration, the (0, 1 2 , 0) occupancy seems to reach a limit, while the ( 1 2 , 0, 0) one further increases. These structural results are discussed in relation with the two different evolutions of the superconducting behaviour previously observed : the enhancement of Tc from 65 K upto 90 K is related to the occupancy of the 0 (4) sites in the CuO chains along the b axis, while filling the 0(5) sites along the a axis mainly affects the a.c. susceptibility amplitude which decreases suddenly from 100% down to about 30%.

Octahedral clusters in molybdenum(II) and rhenium(III) chalcohalide chemistry

Abstract A number of molybdenum(II) or rhenium(III) octahedral cluster compounds, mainly in chalcohalide solid state chemistry, are reported. As shown by single-crystal structure determinations, all these compounds contain (Me 6 L 8 i )L 6 a units which progressively condense when halogen ligands are substituted by chalcogen ligands according to Schafers scheme. The physical properties are discussed in relation to the crystal structures and to electronic band structures determined by recent theoretical calculations.

New families of ternary molybdenum (II) chlorides with octahedral Mo6 clusters

A number of new ternary molybdenum +II chlorides have been synthesized by solid state chemistry methods. These compounds belonging to three families −MIIMo6Cl14, MI2Mo6Cl14 and MIMo6Cl13− are characterized by X-ray data and their main structural features are reported. All these compounds are built from (Mo6Cl8)Cl6 units including octahedral Mo6 clusters. In the first family, these units are linked together by M2+ ions in octahedral Cl6 sites whereas in the second one, the cationic sites (M2Cl6) are splitted or distorted. In the third family, the units are linked together along one direction of space by chlorine bridges and the M+ ions lie in quasi tetrahedral sites.

Scaling in superconducting ceramics

Abstract The formal analogy between the hamiltonian of anX − Y ferromagnet and the pair tunnelling hamiltonian of a granular superconductor allows us to predict a scaling behaviour for the latter. In particular, the voltage-supercurrent characteristic at T = Tc(V ≈ Isa) and the excess conductance above Tc ( σ s ≈ (T − T c ) γ ) are characterized by the critical exponents a and γ. These exponents are measured and similar values are found in both sintered YBaCuO and a granular reference system. The value a ∼- 2 corresponds to three-dimensional (3D) X − Y behaviour and leads us to exclude a possible two-dimensional (2D) Kosterlitz-Thouless transition (for which a = 3) as being responsible for the V − Is characteristic at Tc.