The cluster compound In4Ti1.5Mo0.5Mo14O26 containing Mo14 clusters and the new mono- and bi-capped trioctahedral Mo15 and Mo16 clusters: Synthesis, crystal structure, and electrical and magnetic properties.

International audienceSingle crystals of the new quaternary compd. In4Ti1.5Mo0.5Mo14O26 were obtained by solid state reaction. The crystal structure was detd. by single-crystal X-ray diffraction. In4Ti1.5Mo0.5Mo14O26 crystallizes in the orthorhombic space group Pbca with unit-cell parameters a=9.4432(14) Å, b=11.4828(12) Å, c=20.299(4) Å and Z=4. Full-matrix least-squares refinement on F2 using 3807 independent reflections for 219 refinable parameters resulted in R1=0.0259 and wR2=0.0591. The crystal structure contains in addn. to Mo14 clusters the first examples of mono- and bi-capped trioctahedral Mo14 i.e. Mo15 and Mo16 clusters. The oxygen framework derives from a stacking along the a direction of close-packed layers with sequence (...ABAC...). The Mo-Mo distances range between 2.6938(5) and 2.8420(6) Å and the Mo-O distances between 1.879(5) and 2.250(3) Å, as usually obsd. in molybdenum oxide clusters. The indium atoms form In6+4 bent chains with In-In distances of 2.6682(5) and 2.6622(8) Å and the Ti atoms are in highly distorted octahedral sites of oxygen atoms with Ti-O distances ranging between 1.865(4) and 2.161(4) Å. Magnetic susceptibility measurements confirm the presence of Ti4+ cations and the absence of localized moments on the Mo network. Elec. resistivity measurements on a single crystal of In4Ti1.5Mo0.5Mo14O26 show a semimetallic behavior

Paramagnetic dithiolene complexes as metallo-ligands: ether/thioether coordination.

International audienceThe secondary coordination ability of a paramagnetic nickel dithiolene complex, bearing an ether coordinating function within a nine-membered flexible ring, has been demonstrated in its [NiCl(DMF)(2)](+) complex, through coordination by both ether and thioether functions, allowing for a ferromagnetic interaction between both paramagnetic entities

Chiral electron-rich bis(cyclopentadienyl) dithiolene molybdenum complexes

International audienceEnantiomerically pure electron rich Cp2Mo(dithiolene) complexes have been synthesized from the enantiopure dithiolene ligands, namely the (R)- and the (S)-3(1-phenylethyl)-1,3-thiazoline-2-thione-4,5-dithiolate ligands. These heteroleptic molybdenum complexes act as very good electron donors, as demonstrated through electrochemical investigations. Both isomers form charge transfer salts with TCNQ with a 1:1 stoechiometry which have been characterized by single crystal X-ray diffraction, EPR and UV–vis spectroscopic investigations. Circular dichroism (CD) experiments were also carried out on the neutral (R) and (S) enantiomers as well as on the mono oxidized species of these Cp2Mo dithiolene complexes

Electrical Resistivity Behavior and VRH Transport Mechanism in Semiconducting La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0.10≤x≤0.25) Manganites

International audienceThe transport properties and conduction mechanism in La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0≤x≤0.3) have been investigated. The undoped samples show metal-semiconductor transition with a peak of resistivity at a temperature T P , whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr3+ and Fe3+ ions leads to the increase of resistivity because the simultaneous substitution of Fe3+ and Cr3+ for Mn3+ reduces the number of available hopping sites for the Mn e g↑ electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott's relation obey the variable range hopping (VRH) mechanism

Dithiolene complexes as metallo-ligands: a crown-ether approach

International audienceA nickel dithiolene complex substituted with crown ether cyclic moieties incorporating four O atoms, abbreviated as [Ni(S2O4)2]1−,0, is isolated in its radical anionic (as Na+ salt) and neutral forms. The Na+ cation is six-coordinated with short Na[cdots, three dots, centered]O distances (2.46-2.52 Å), involving two crown ether moieties of two different complexes. The oxidized neutral complex [Ni(S2O4)2]0 was also isolated and structurally characterized. In the absence of alkaline cations during the synthesis, a mixed salt associating [Ni(S2O4)2]1− with Ni2+ was isolated, and formulated as (Ni,H2O)[Ni(S2O4)2]2, with the Ni2+ cation weakly bonded to two crown ether moieties. The salt exhibits an unprecedented solid state association with extremely short S[cdots, three dots, centered]S intermolecular contacts [3.332(2) Å], leading to a pairing of the radical [Ni(S2O4)2]− into antiferromagnetic uniform spin chains

Probing magnetic interactions in columnar phases of a paramagnetic gold dithiolene complex

International audienceA novel radical gold dithiolene complex exhibits a hexagonal columnar mesophase, as confirmed by optical microscopy , DSC analysis and X-ray diffraction . The extent of delocalization of the spin density in such a complex was analyzed by EPR . Temperature dependent magnetization measurements reveal that the global magnetic moment is remarkably affected at the liquid-crystalline phase transition with a marked hysteresis signature, rare behavior among the few described paramagnetic discotic phases. In addition, these molecules were found to strongly aggregate in solution into one-dimensional fibers with a mean diameter of 60 nm extending over micrometres, leading to the formation of gel-like structures. These fibers are stable and can be isolated on surfaces. The gelation of the system can also be detected by temperature-dependent magnetic measurements

Electrical and magnetic properties of La0.67Ba0.33Mn1−x (Me) x O3 perovskite manganites: case of manganese substituted by trivalent (Me = Cr) and tetravalent (Me = Ti) elements

International audienceThe effects of non-magnetic Ti4+ substitution on the structural, electrical and magnetic properties of La0.67Ba0.33Mn1−x Ti x O3 (0≤x≤0.1) are investigated and compared to those existing in La0.67Ba0.33Mn1−x Cr x O3 (magnetic Cr3+). The structural refinement by the Rietveld method revealed that Ti-doped samples crystallize in the cubic lattice with space group Pm3¯m , while samples with Cr crystallize in the hexagonal setting of the rhombohedral R3¯C space group for identical contents of dopant. The most relevant structural features are an increase of the lattice parameters, of the cell volume and of the inter-ionic distances with increasing Ti doping level. Both series of samples show a decrease of the paramagnetic-ferromagnetic transition temperature when the amount of chromium or titanium increases. Transport measurements show that when increasing the metal doping, the resistivity increases whereas the metallic behavior of the parent compound La0.67Ba0.33MnO3 is destroyed. For a substitution higher than 5 at.% of Ti and 10 at.% of Cr, the samples exhibit a semiconducting behavior in the whole range of temperature, for which the electronic transport can be explained by variable range hopping and/or small polaron hopping models

Synthesis, crystal structure, and electrical and magnetic properties of BaMo6Te6: A novel reduced molybdenum telluride containing infinite chains of trans-face shared Mo6 octahedra

Accepted 29 August 2014International audiencePowder samples and single crystals of the new ternary compound BaMo6Te6 were obtained by solid state reaction. The structure was determined by single-crystal X-ray diffraction. BaMo6Te6 crystallizes in the hexagonal space group P63/m (No. 176) with unit-cell parameters a=9.3941(2) Å, c=4.5848(1) Å and Z=1. Full-matrix least-squares refinement on F2 using 452 independent reflections for 17 refinable parameters resulted in R1=0.0208 and wR2=0.0539. The structure consists of one-dimensional infinite chains of trans-face shared Mo6 octahedra capped by Se atoms. These chains that are running along the c axis are separated from each other by nine-coordinate Ba atoms. Resistivity measurements on a single crystal indicated that the BaMo6Te6 compound is metallic down to 160 K and semiconductor below. Magnetic susceptibility measurements showed that BaMo6Te6 is weakly diamagnetic with no anomaly at the metal-semiconductor transition

Synthesis, Crystal Structure, and Electrical and Magnetic Characterizations of the Monoclinic Compounds Ln 3 Mo 4+ x Si 1– x O 14 (Ln = La, Ce, Pr, and Nd; x = 0 and 0.35) Containing Mo 3 Clusters and Mo 2 Dimers

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