Search results for "Yttrium"

Zirconium, hafnium and yttrium complexes containing two linked amido— tetramethylcyclopentadienyl ligands: Synthesis, reactivity and molecular struct…

1998

Abstract Zirconium and hafnium complexes M(η5: η1−C5Me4SiMe2NR′)xCl(4−2x) (M = Zr, Hf; x = 1, 2; R′ = iPr, tBu) containing one or two linked amido-tetramethylcyclopentadienyl ligands C5Me4SiMe2NR′ have been synthesized by the reaction of the dilithium derivative Li2(C5Me4SiMe2NR′) with MCl4(THF)2. The crystal structure of the hafnium complex Hf(η5: η1−C5Me4SiMe2NiPr)2 has been determined by a single-crystal X-ray diffraction study and shows a C2-symmetric helical metallocene, in which the amido ligands are bonded as π-donor ligands with Hf—N bond lengths of 2.115(2) A. The isoelectronic heterobimetallic yttrium complex Li[Y(η5: η1−C5Me4SiMe2NCH2CH2OMe)2] reacts with phenylacetylene to give …

MOCVD deposition of YSZ on stainless steels

2003

Abstract Yttria stabilized zirconia was deposited on stainless steel using the metal–organic chemical vapor deposition (MOCVD) technique, from β-diketonate precursors. The variation of the evaporation temperatures of yttrium and zirconium precursor allowed to control the level of Y within the film. Over the temperature range 125–150 °C, the Y content increased from 2.5 to 17.6 at.%. X-ray diffraction (XRD) analyses evidenced tetragonal phase of zirconia when the Y content was below 8 at.%, and cubic phase for higher concentration. Sputtered neutral mass spectrometry (SNMS) profiles confirmed that the control and stability of Y precursor temperature were of major importance to guarantee the …

Y:BaZrO3 Perovskite Compounds I: DFT Study on the Unprotonated and Protonated Local Structures

2011

Y-doped BaZrO(3) derivatives were studied by density functional theory (DFT) to investigate the local arrangements of the octahedral sites in Pm3m cubic frameworks. Single- and double substitution of zirconium by yttrium were considered, including in the presence of a nearby oxygen vacancy. Although the structural symmetry of undoped barium zirconate was not modified after yttrium doping, the presence of yttrium induced several differences in the oxygen sites around it, according to the local geometrical arrangement of yttrium in the host matrix. As an example, the differences between such oxygen sites were shown in the presence of a proton. In this case, different stabilization energies ch…

Y:BaZrO 3 Perovskite Compounds II: Designing Protonic Conduction by using MD Models

2011

The proton dynamics in Y-doped BaZrO(3) derivatives, in particular the different dopant environments within a Pm3m cubic framework, were studied by using classical molecular dynamics (MD) calculations. Single- and double substitution of zirconium by yttrium atoms was considered. The presence of yttrium induced variations in the surrounding oxygen sites, according to their local geometrical arrangements. The differences among such distinct oxygen sites became evident when protons interacted with them and upon changes in the temperature. So, different proton transfer pathways, which had different energy barriers, characterized the topologically different oxygen sites. The experimental proton-…

CCDC 279767: Experimental Crystal Structure Determination

2007

Related Article: L.G.Hubert-Pfalzgraf, L.Cauro-Gamet, A.Brethon, S.Daniele, P.Richard|2007|Inorg.Chem.Commun.|10|143|doi:10.1016/j.inoche.2006.09.008

Chiral Lanthanocene Derivatives Containing Two Linked Amido−Cyclopentadienyl Ligands:  Heterobimetallic Structure and Lactone Polymerization Activity

1997

Reaction of 2 equiv of dilithium amido−cyclopentadienide Li2(C5R4SiMe2NCH2CH2X) (C5R4 = C5Me4, C5H3tBu; X = OMe, NMe2) with anhydrous LnCl3 (Ln = Y, Lu) gave C2-symmetric complexes of the type Li[Ln(η5:η1-C5R4SiMe2NCH2CH2X)2] containing a heterobimetallic core. The molecular structure of Li[Y(η5:η1-C5Me4SiMe2NCH2CH2OMe)2] was determined by single-crystal X-ray structural analysis, which showed it to exhibit both a pseudotetrahedral yttrium as well as a tetrahedral lithium center. In accordance with a formal 20-electron configuration at the rare earth metal center Ln, the amido-nitrogen atoms are shown to be pyramidalized. In the case of Li[Y(η5:η1-C5H3tBuSiMe2NCH2CH2X)2], mixtures of the tw…

Rare earth metal-based catalysts for the polymerization of nonpolar and polar monomers

2001

Abstract The synthesis of rare earth metal half-sandwich hydrido complexes [Ln (h5:h1-C5Me 4SiMe2NCMe3) (THF) (µ-H) ] 2 (Ln = Y, Lu) through s-bond metathesis of the easily accessible alkyl complexes [Ln (h5:h1-C5Me 4SiMe2NCMe3) (CH2 SiMe3) (THF) ] was developed. The dimeric yttrium hydrido complexes are highly fluxional, and a monomer-dimer equilibrium is present. They were tested as single-site, single-component catalysts for the polymerization of ethylene and styrene, as well as alkyl acrylate and acrylonitrile. The hydrido complexes polymerize ethylene slowly and form isolable mono (insertion) products with styrene. The yttrium n-alkyl complexes [Y (h5:h1-C5Me 4SiMe2NCMe3) (R) (THF) ] […

Erratum: “Nanoscale x-ray imaging of spin dynamics in yttrium iron garnet” [J. Appl. Phys. 126, 173909 (2019)]

2021

Macro-micro relationship in nanostructured functional composites

2012

This paper examines the results of the characterization of two functional composites: Poly(methyl methacrylate) (PMMA)-Ce:YAG (yttrium aluminium garnet doped with cerium) and PMMA-cobalt hexacyanoferrate (CoHCF). The composites were prepared as possible emitters in the fields of lighting thermal sensors. The prepared composites were char- acterized using transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) spectroscopy, thermogravi- metric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) analyses to study the correlation between micro and macro characteristics. We found that the molecular interactions of the two different fill…

Highly Syndiotactic or Isotactic Polyhydroxyalkanoates by Ligand-Controlled Yttrium-Catalyzed Stereoselective Ring-Opening Polymerization of Function…

2017

International audience; Reported herein is the first stereoselective controlled ROP of a specific family of racemic functional β-lactones, namely 4-alkoxymethylene-β-propiolactones (BPL(OR) s). This process is catalyzed by an yttrium complex stabilized by a nonchiral tetradentate amino alkoxy bisphenolate ligand _ONOO(R'2) ₍2-) , which features both a good activity and a high degree of control over the molar masses of the resulting functional poly(3-hydroxyalkanoate)s. A simple modification of the R' substituents in ortho and para position on the ligand platform allows for a complete reversal from virtually pure syndioselectivity (Ps up to 0.91 with R'=cumyl) to very high isoselectivity (Pi…