New Pyrochlore Pb[In0.5 Sb1.5]O6.5

From the study of the hypothetical series Pb[PbIn_c–2pSb_c]O_6+p (O ? p < 1; 0 ? c < 2), the existence of the cubic pyrochlore Pb₂^II[In_0.5Sb_1.5]O_6.5 has been established. This compound was obtained as an orange yellow powder, S.G. Fd4 m (No. 227), Z = 8, a = 10.5892(1) Å, V = 1187.38(3) ų, D_c = 8.48 M gm^?3. For Pb in 16(c) positions, In and Sb (1:3) randomly distributed in 16(d), oxygen atoms in 48(f) and in a half of the 8(a) sites, and oxygen positional parameter x = 0.429 (origin at center, 3 m), R = 0.062. The apparent interatomic distances (Å) are determined: Pb? O = 2.612; (In, Sb)? O = 2.019.     

Oxygen-release/storage properties of Ce0.5M0.5O2 (M = Zr, Hf) oxides: interplay of crystal chemistry and electronic structure

Fluorite-type Ce0.5Zr0.5O2 and Ce0.5Hf0.5O2 have been synthesized by a solution combustion route, and their oxygen release and reduction have been investigated up to 850 degrees C. On reduction, the zirconium system forms two pyrochlore phases, Ce2Zr2O7 (pyrochlore-I) and Ce2Zr2O6.2 (pyrochlore-II), while the hafnium system forms only a disordered fluorite phase with the composition Ce0.5Hf0.5O1.77, under the same experimental conditions. The crystal structures of the reduction products have been characterized by powder X-ray diffraction and Rietveld refinement, and their electronic structures have been investigated by photoelectron spectroscopy and electrical conductivity measurements. Pyrochlore-I (a = 10.6727(4) A) is a semiconductor, while pyrochlore-II (a = 10.6463(8) A) is a good conductor (with a nearly temperature independent resistivity of approximately 2.5 ohm.cm in the 400-1000 K range). X-ray photoelectron spectroscopy (XPS) shows an admixture of Ce(5d,6s) with Zr(4d) and O(2p) and a significant density of states near EF in the highly reduced pyrochlore-II phase. The changes have been rationalized in terms of a qualitative energy band scheme that brings out the special role of zirconium vis-à-vis hafnium in the reduction/oxygen release properties of Ce0.5Zr0.5O2 and Ce0.5Hf0.5O2.     

As-5、[As5M]-、[As5MAs5]2- (M=Ti,Zr, Hf)的结构和芳香性

用密度泛函理论(DFT)研究了As-5、[As5M]-和[As5MAs5]2- (M=Ti, Zr, Hf)的结构、频率、能量以及芳香性, 详细讨论了体系中不同类型的键和电子如化学键、孤对电子、核电子等对总的核独立化学位移(NICS)的影响. 结果表明, As-5、[As5M]-和[As5MAs5]2-的基态结构分别具有D5h、C5v和D5h对称性, 而且都具有芳香性. As-5 (D5h)的芳香性主要来源于As—As π键和As—As σ键的作用. [As5M]-(C5v)中各种As—M键的NICS分割值占主要优势, 其次是As—As之间形成的σ键. [As5TiAs5]2-(D5h)中, As—As π键的作用占主要优势. [As5ZrAs5]2-(D5h)中, As—As π键对体系总的NICS贡献相对减小, 而As—Zr键的作用增强. [As5HfAs5]2-(D5h)的芳香性主要来自As—Hf键的作用.     

Preparation and physical properties of early-late heterobimetallic compounds featuring Ir-M bonds (M = Ti, Zr, Hf)

Treatment of Cp*Ir N(t)Bu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N(t)Bu)MCp(2) (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir-M bond, to afford Cp*Ir(μ-N(t)Bu)(μ-H)MCp(2)OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp(2)Zr(H)Cl in the presence of Me(3)SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S(8) and aryl azides to insert an S-atom or aryl azide fragment into the metal-metal bond, yielding Cp*Ir(μ-N(t)Bu)(μ-S)HfCp(2) (6-Hf) and Cp*Ir(μ-N(t)Bu)(N(3)Ph)HfCp(2) (4-Hf), respectively. Heating 4-Hf results in N(2) extrusion to form Cp*Ir(μ-N(t)Bu)(NPh)HfCp(2) (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir-Zr heterobimetallics.     

Bis(triphenylzinn-und-blei)hyponitrit [(C6H5)3M]2N2O2 (M = Sn,Pb)

Triphenyltin and lead hyponitrite are prepared from the triphenylmetal iodides and Ag₂N₂O₂. The thermal decomposition and the infrared spectra of the compounds have been studied.     

Hydrothermal Synthesis of Pb_(1-1.5x)La_xZr_(0.5)Ti_(0.5)O_3 (x = 0.01-0.06) Nanocrystallites

Lanthanum doped lead zirconate titanate (PLZT) ceramics display excellent electrooptic and photostriction properties because of the existence of cavities in the perovskite structure1-3. The PLZT powders are conventionally prepared by solid state reaction4-5, and the wet chemical methods such as sol-gel techniques are then introduced6-7. However, the homogeneity, morphology and size of the particles, which greatly affect the sinterability and the property of the resulting ceramics, are dif…     

钛,锆和铪羰基化合物M(CO)_n(M=Ti,Zr,Hf;n=4～7)的理论研究

利用密度泛函方法对标题化合物的平衡几何、热化学及振动频率进行了理论预测,发现这3种金属原子都有相似的M(CO)n(n=4～7)结构.全局最低构型对M(CO)7都是单态C3v戴帽八面体7S-1,对M(CO)6都是三重态D3d畸变八面体6T(而对应的单重态M(CO)5仅比它低不到21 kJ·mol-1).对M(CO)n(n=5,4)都是三重态6S-1,其构型分别为从6T中移去1个或2个CO基的衍生物5T和4T.此外,五重态的D3h的三角双锥M(CO)5和单态的Td四面体M(CO)4以及能量更高的含有C和O同时与金属成键的独特配位CO基的M(CO)6和M(CO)3也被发现.最后,给出M(CO)7→M(CO)6+CO反应的离解能.并讨论了金属18价电子的Ti(CO)7存在的可能性.     

Comparing the Atomic Structures of Binary MO2-SiO2 (M = Ti, Zr or Hf) Xerogels

The incorporation of transition-metal oxides into silica can give materials with useful optical, electronic or catalytic properties. For example, ZrO₂-SiO₂ and HfO₂-SiO₂ materials are of interest due to their high dielectric constants. Here we present a comparison of extended X-ray absorption fine structure and small-angle X-ray scattering results for acid-catalysed binary (MO₂) _x (SiO₂)_{1 – x} (M = Ti, Zr or Hf) xerogels, with x up to 0.4 and heat treatments up to 750°C. Detailed observations for TiO₂-SiO₂ and ZrO₂-SiO₂ xerogels provide a basis for interpretation of new results for HfO₂-SiO₂ xerogels. At low concentrations metal atoms are homogeneously incorporated into the silica network. Ti adopts coordinations of 4 or 6, and Zr and Hf both adopt higher coordination of 6 or 7 (the larger coordinations being due to ambient moisture). At higher concentrations, phase separation of metal oxide occurs. Such regions become clearly separated from the silica network for TiO₂, but remain very finely mixed with silica network for ZrO₂ and HfO₂.     

Synthesis and Crystal Structure of Te6[MCl6] (M = Zr,Hf), Containing a Polymeric Chalcogen Cation (Te62+)n

The reaction of tellurium, tellurium tetrachloride, and ZrCl₄ or HfCl₄, respectively, under the conditions of chemical vapour transport in a temperature gradient 220 → 200 °C yields black crystals of Te₆[ZrCl₆] and Te₆[HfCl₆]. While Te₆[ZrCl₆] is formed almost quantitatively, Te₆[HfCl₆] is always accompanied by neighbored phases such as Te₄[HfCl₆] and Te₈[HfCl₆]. The crystal structures of Te₆[ZrCl₆] (orthorhombic, Pbcm, a = 1095.4(1), b = 1085.2(1), c = 1324.5(1) pm) and Te₆[HfCl₆] (a = 1094.8(2), b = 1086.3(2), c = 1325.0(2) pm) are isotypic and consist of one‐dimensional polymeric (Te₆²⁺)_n cations and of discrete, only slightly distorted octahedral [MCl₆]^2‐ anions (M = Zr, Hf). The cations are build of five membered rings which are connected via single Te atoms to a polymer ‐Te‐Te₅‐Te‐Te₅‐. Out of the six Te atoms of the asymmetric unit of the chain four atoms exhibit two bonds and two atoms exhibit three bonds. The connecting, threefold coordinated Te atoms of the five membered rings carry formally the positive charges. In consistence with the assumption of the presence of throughout localized bonds eH band structure calculations for Te₆[ZrCl₆] show semiconducting behaviour with a band gap of 1.8 eV.     

Magnetische Messungen anHeusler-Phasen (Co,Mn)2 XY (X=Ti,Zr,Hf und Mn;Y=Ge und Sn)

Magnetic measurements onHeusler alloys (Co,Mn)₂ XY have been performed. With a few exceptions there is no enhancement of ferromagnetism while substituting cobalt by manganese. The results can be explained by a partially antiferromagnetic ordering of the manganese atoms.     

Fluoride mit zweiwertigem Silber. Zur Kenntnis der Verbindungen AgII[MF6] mit M = Ge,Sn, Pb,Ti, Zr,Hf, Rh,Pd, Pt.

Fluorides with divalent Silver. On the compounds Ag^II[MF₆] with M = Ge, Sn, Pb, Ti, Zr, Hf, Rh, Pd, Pt. For the first time AgTiF₆, AgGeF₆, AgSnF₆ AgPbF₆ (all light-blue), AgRhF₆ (black), AgPdF₆ (d.brown), AgPtF₆ (brownviolet) as well as AgZrF₆ and AgHfF₆ (both deeply blueviolet) are prepared. AgSnF₆, AgPbF₆ and AgPdF₆ obey the Curie-Weiss Law (m? = 2,0 m?_B, small θ-value). In the case of AgZrF₆ and AgHfF₆ there is a strong magnetic exchange between Ag²⁺ ions; this may be the cause for the unexpected deep colour.     

Magnetoelectric perovskite (Bi0.5Pb0.5)(Fe0.5Zr0.5)O3: Preparation,structural and magnetic properties

The perovskite (Bi_0.5Pb_0.5)(Fe_0.5Zr_0.5)O₃ was synthesized by solid-state reaction in an attempt to find magnetoelectric materials, in which ferroelectricity and ferromagnetism coexist. This complex perovskite has been studied by X-ray and neutron powder diffraction in combination with magnetic measurements. The compound crystallizes in the orthorhombic space group Pbam with a ～ √2a_p, b ～ 2√2a_p and c ～ 2a_p (with a_p ～ 4.057 Å). The field and temperature dependence of the magnetization combined with neutron diffraction data showed antiferromagnetic behavior with the Neel temperature, T_N ～ 450 K. Rietveld refinements of neutron powder diffraction data collected at different temperatures, between 10 and 700 K, have been carried out in order to extract information about the thermal evolution of the nuclear and magnetic structures. A distorted orthorhombic perovskite structure was found within the whole temperature interval. The Bi/Pb and Fe/Zr ions were found to be partially ordered over the perovskite A-site and disordered over the B-site. The neutron diffraction patterns of the (Bi_0.5Pb_0.5)(Fe_0.5Zr_0.5)O₃ sample showed evidence of a long-range magnetic ordering below T_N with a propagation vector k = (0,0,0) and an antiferromagnetic arrangement of the magnetic moments of the Fe³⁺ cations in the B-site. This is consistent with an A_y-type magnetic structure. The factors governing the structural and magnetic properties of (1 ? x)BiFeO₃–xPbZrO₃ solid solutions are discussed and compared with those of pure BiFeO₃ and PbZrO₃. A solid solution strategy for developing magnetoelectric properties in BiFeO₃-based compounds is described, with the aim of realizing both a spontaneous polarization and magnetization at room temperature.     

Magnetische Messungen anHeusler-Phasen (Co,Ni)2 XY (X=Ti,Zr, Hf,V und Mn;Y=Ge und Sn)

Magnetic measurements onHeusler alloys (Co, Ni)₂ XY are performed. The transitions from ferromagnetic to paramagnetic behaviour in some systems are of special interest.

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Hydrogen absorption by intermetallics M2Fe (M = Zr,Hf, Ti) and their effect on the catalytic aromatization of ethane

The absorption properties of the hydride-forming intermetallics M₂Fe(M = Zr, Hf, Ti) and their effect on the aromatization of ethane over Pt,Ga/HCVM catalyst within the temperature range 400–450 °C are studied. The absorption capacity of the intermetallics under aromatization conditions and their efficiency as hydrogen acceptors are shown to decrease in the order Zr₂Fe > Ti₂Fe > Hf₂Fe.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1726–1729, October, 1994.     

Co-ordination studies of tris(dimethylamino)phosphine oxide: Reactions with the covalent metal halides MCl3 (M = Ti,V and Cr), MCl4 (M = Ti,Zr, Hf and Sn) and SnI4

Complexes of the type MCl₃·3L where M = Ti, V and Cr; L = (Me₂N)₃P = O(HMPA) are described. Conductivity, IR and UV-visible spectral data correlates with a proposed fac-octahedral (C_3v) configuration. For the Cr(III) species, geometrical isomerisation has been observed leading to isolation of the mer-isomer (C_2v). Spectral (¹H, ³¹P and ¹³C NMR and far IR) measurements for the six co-ordinate series MCl₄·2HMPA (M = Ti, Zr, Hf and Sn) and SnI₄·2HMPA correlate fully with a trans(D_4h) arrangement of the ligands. Complexes 2TiCl₄·HMPA and SnCl₄·HMPA have been isolated and characterised. Spectral properties of these diamagnetic compounds are related to the confacial bioctahedral and dimeric halogen-bridged (C_2h) structures respectively.