Zur Kenntnis von Sr2CuO2Br

Inhaltsübersicht. Sr₂CuO₂Br wurde in geschlossenen Cu-Bömbchen dargestellt und an Einkristallen röntgenographisch untersucht (a = 4,0235; c = 28,5103 A; Raumgruppe D⁵_2d–R$3m). Sr²⁺ besitzt oktaedrische Koordinationspolyeder aus je drei Br^– und O^2–. Die Oktaeder sind in Doppelschichten angeordnet und werden von hantelförmig koordinierten Cu⁺-Ionen längs [001] verknüpft. About Sr₂CuO₂Br Single crystal of the unknown compound Sr₂CuO₂Br were prepared in closed Cu-tubes and examined by single X-ray diffractometer investigation (a = 4.0235; c = 28.5109 A; space group D⁵_3d–R$3m). Sr²⁺ has octahedral coordination of 3 Br^– and 3 O^2–. Cu⁺ shows a dumb-bell-like O^2– surrounding.     

Preparation of Sr7Mn4O13F2 by the topotactic reduction and subsequent fluorination of Sr7Mn4O15

The topotactic reduction and subsequent fluorination of Sr7Mn4O15 yields a phase of composition Sr7Mn4O13F2. Characterization of this phase utilizing powder neutron diffraction and 19F NMR shows that the fluoride ions are located on a single anion site, the same crystallographic site that is vacant in the reduced intermediate Sr7Mn4O13.     

über Erdalkalimetalloxocuprate,VIII Zur Kenntnis von Sr2CuO2Cl2

On Alkaline Earth Oxocuprates VIII. About Sr₂CuO₂Cl₂ Sr₂CuO₂Cl₂ was prepared and investigated by single crystal X – ray work (space group D–Immm, a = 3.975, c = 15.618 Å). Sr₂CuO₂Cl₂ is isotypic with K₂NiF₄ – compounds and shows an octahedral configuration for Cu²⁺. Cl^? occupies trans-positions of the octahedral Cu²⁺/O^2? polyhedron. A discussion with related compounds (Sr₂CuO₃ and Nd₂CuO₄) explains the observed distribution of O^2? and Cl^?.     

Optically active vibrations of lanthanum copper oxide compound (La2CuO4)

Normal coordinate analysis of the optically active vibrations of lanthanum copper oxide has been made, with the assumption of a perovskite K₂NiF₄ structural model. On the basis of the results of this treatment, all of the observed bands so far reported have been successfully assigned to the intramolecular CuO vibrations and the optically active lattice vibrations (the motions of La against CuO₆ octahedra, abbreviated to La---CuO₆). The force constants concerning CuO and LaO bonds have been obtained within the framework of the modified valence force fields. It has been found that the present normal coordinate analysis based on a whole crystal is useful for assigning the optically active vibrations (normal modes) at the center of the Brillouin zone in La₂ CuO₄.     

Electrode properties of Sr doped La2CuO4 as new cathode material for intermediate-temperature SOFCs

High performance La_2−xSr_xCuO_4−δ (x = 0.1, 0.3, 0.5) cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFCs) were prepared and characterized. The investigation of electrical properties indicated that La_1.7Sr_0.3CuO₄ cathode has low area specific resistance (ASR) of 0.16 Ω cm² at 700 °C and 1.2 Ω cm² at 500 °C in air. The rate-limiting step for oxygen reduction reaction on La_1.7Sr_0.3CuO₄ electrode changed with oxygen partial pressure and measurement temperature. La_1.7Sr_0.3CuO₄ cathode exhibits the lowest overpotential of about 100 mV at a current density of 150 mA cm⁻² at 700 °C in air.     

Über Oxocuprate. XV Zur Kristallstruktur von Seltenerdmetalloxocupraten: La2CuO4, Gd2CuO4

About Oxocuprates. XV. The Crystal Structure of Rare Earth Oxocuprates: La₂CuO₄, Gd₂CuO₄ Gd₂CuO₄ and La₂CuO₄ are examined by single crystal X-ray methods. Gd₂CuO₄ is isotypic with Nd₂CuO₄, La₂CuO₄ however shows a slightly distorted K₂NiF₄ structure. Cu²⁺ has square (Gd₂CuO₄) or octahedral (La₂CuO₄) coordination. La₂CuO₄ is the only compound in the system of Rare Earth cuprates with K₂NiF₄-type structure.     

Tellurium-bridged manganese carbonyl clusters: synthesis and structural transformations of [Te4Mn3(CO10]-, [Te2Mn3(CO)9]2-, [Te2Mn3(CO)9]-, and [Te2Mn4(CO)12]2-

The reactions of appropriate ratios of K2TeO3 and [Mn2(CO)10)] in superheated methanol solutions lead to a series of novel cluster anions [Te4Mn3(CO)10] (1), [Te2Mn3(CO)9]2- (2), [Te2Mn3(CO)9]- (3), and [Te2Mn4(CO)12]2- (4). When cluster 1 is treated with [Mn2(CO)10]/KOH in methanol, paramagnetic cluster 2 is formed in moderate yield. Cluster 2 is oxidized by [Cu(MeCN)4]BF4 to give the closo-cluster [Te2Mn3(CO)9]- (3), while treatment of 2 with [Mn2(CO)10]/KOH affords the closo-cluster 4. IR spectroscopy showed that cluster 1 reacted with [Mn2(CO)10] to give cluster 4 via cluster 2. Clusters 1-4 were structurally characterized by spectroscopic methods or/and X-ray analyses. The core structure of 1 can be described as two [Mn(CO)3] groups doubly bridged by two Te2 fragments in a mu2-eta2 fashion. Both [Mn(CO)3] groups are further coordinated to one [Mn(CO)4] moiety. Cluster 2 is a 49 e- species with a square-pyramidal core geometry. While cluster 3 displays a trigonal-bipyramidal metal core, cluster 4 possesses an octahedral core geometry.     

Perovskite related phases in the Sr5Nb4O15 - SrTiO3 - Sr4Nb2O9 system

Phase relations have been investigated within the Sr₅Nb₄O₁₅−SrTiO₃−Sr₄Nb₂O₉ region of the SrO−Nb₂O₅−TiO₂ system with a view to clarifying the occurrence of fully oxidised perovskite related phases. Overall phase analysis was carried out by powder X-ray diffraction and microstructures were clarified by transmission electron microscopy. There is only one main composition triangle in this area at 1350°C. The tie-line between Sr₅Nb₄O₁₅ and SrTiO₃ contains a homologous series of hexagonal layered perovskite phases including Sr₆Nb₄TiO₁₈ and Sr₇Nb₄Ti₂O₂₁. The phase Sr₄Nb₂O₉ is a nonstoichiometric phase with a disordered perovskite structure. There is some extension of this phase along the Sr₄Nb₂O₉−SrTiO₃ tie-line, but SrTiO₃ does not show a significant composition range. Samples with a composition Sr₄Nb₂O₉, when heated at 900°C show several ordered modifications. Samples along the Sr₄Nb₂O₉−SrTiO₃ tie-line which are annealed at 900°C contain these ordered materials together with samples showing considerable short range order which increases as the Ti content increases.     

Selective deintercalation of apex over face-shared oxide ions in the topotactic reduction of Sr7Mn4O15 to Sr7Mn4O12

Sodium hydride selectively deintercalates the apex rather than face-shared oxide ions within the structure of Sr(7)Mn(4)O(15) leading to the formation of the structurally related reduced phase Sr(7)Mn(4)O(12).     

Metastabile Oxometallate der Lanthanoidmetalle:.Zur Kenntnis von Sr3Pr4O9 und Sr3La2Sm2O9 mit einem Beitrag über SrPr2O4

Metastable Compounds of Rare Earth Oxides. About Sr₃Pr₄O₉ and Sr₃La₂Sm₂O₉ with a Remark about SrPr₂O₄ Sr₃Pr₄O₉ (A) and Sr₃La₂Sm₂O₉ (B) are for the first time prepared and investigated by X-ray single crystal work. Both compounds crystallize with monoclinic symmetry (space group C_s⁴? Cc, Z = 4) with (A) a = 11.468; b = 7.262; c = 13.218 Å; β = 115.61°, (B) a = 11.518; b = 7.263; c = 13.290 Å; β = 115.61°. (A) and (B) are metastable with high disorder in the metal positions. All of the metal positions are occupied with a statistical distribution of Sr²⁺ and Ln³⁺. (A) decomposes in the hitherto unknown compound SrPr₂O₄. It belongs to the calciumferrite type compounds.     

Family of double-cubane Mn4Ln2 (Ln = Gd, Tb, Dy, Ho) and Mn4Y2 complexes: a new Mn4Tb2 single-molecule magnet

The synthesis and characterization of a family of Mn(2)(III)Mn(2)(II)Ln(III)(2) complexes (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)) of formula [Mn(4)Ln(2)O(2)(O(2)CBu(t))(6)(edteH(2))(2)(NO(3))(2)] are reported, where edteH(4) is N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine. The analogous Mn(4)Y(2) (5) complex has also been prepared. They were obtained from reaction of Ln(NO(3))(3) or Y(NO(3))(3) with Mn(O(2)CBu(t))(2), edteH(4), and NEt(3) in a 2:3:1:2 molar ratio. The crystal structures of representative 1 and 2 were obtained, and their core consists of a face-fused double-cubane [Mn(4)Ln(2)(μ(4)-O(2-))(2)(μ(3)-OR)(4)] unit. Such double-cubane units are extremely rare in 3d metal chemistry and unprecedented in 3d-4f chemistry. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1-5 were carried out. Fitting of dc χ(M)T vs T data for 5 gave J(bb) (Mn(III)···Mn(III)) = -32.6(9) cm(-1), J(wb) (Mn(II)···Mn(III)) = +0.5(2) cm(-1), and g = 1.96(1), indicating a |n, 0, n> (n = 0-5) 6-fold-degenerate ground state. The data for 1 indicate an S = 12 ground state, confirmed by fitting of magnetization data, which gave S = 12, D = 0.00(1) cm(-1), and g = 1.93(1) (D is the axial zero-field splitting parameter). This ground state identifies the Mn(II)···Gd(III) interactions to be ferromagnetic. The ac susceptibility data independently confirmed the conclusions about 1 and 5 and revealed that 2 displays slow relaxation of the magnetization vector for the Mn(4)Tb(2) analogue 2. The latter was confirmed as a single-molecule magnet by observation of hysteresis below 0.9 K in magnetization vs dc field scans on a single crystal of 2·MeCN on a micro-SQUID apparatus. The hysteresis loops also displayed well-resolved quantum tunneling of magnetization steps, only the second 3d-4f SMM to do so.     

Crystal structures of Sr4Sn2Se9 and Sr4Sn2Se10 and the oxidation state of tin in an unusual geometry

The new ternary selenostannates Sr(4)Sn(2)Se(9) and Sr(4)Sn(2)Se(10) have been synthesized by heating the elements at 1023 K in an argon atmosphere. Their structures were determined by single-crystal X-ray methods. Sr(4)Sn(2)Se(9) crystallizes in a new structure type (Pbam, a = 12.042(2) A, b = 16.252(3) A, c = 8.686(2) A, Z = 4) with Sn(2)Se(6)(4-), SnSe(4)(4-), and Se(2)(2-) subunits. Sr(4)Sn(2)Se(10) (P2(1)2(1)2, a = 12.028(2) A, b = 16.541(3) A, c = 8.611(2) A, Z = 4) has a similar structure with Se(3)(2-) triangles instead of Se(2)(2-) dumbbells. Strontium is 8-fold-coordinated by selenium in both cases. The opening angles between tin and the terminal selenium atoms in the Sn(2)Se(6) subunits are close to 160 degrees , which is nearer a typical Sn(2+) coordination geometry than classical SnSe(4) tetrahedra. This result suggests the tin oxidation state in the Sn(2)Se(6) units to be lower than the expected Sn(4+). This question is examined by self-consistent LMTO and LAPW band structure calculations expanded by the Bader analysis of the charge density to assign reliable atomic charges.     

Über Oxocuprate,XXVI Synthese und Struktur eines Oxohalogenocuprat(I): Sr2CuO2Cl

Single crystals of Sr₂CuO₂Cl were prepared in a closed system of Ag- and quartz-tubes. The colorless crystals are extremly sensitive against moisture. X-ray investigation proves a trigonal symmetry (a=400.3;c-2767.9 pm, space group P3₁21-D ₃ ⁴ ). Sr²⁺ has a distorted octahedral coordination of 3 O^2– and 3 Cl^–. Cu⁺ shows a dumbbell like O^2– surrounding. The O-Cu-O bond angle (176.5°) differs from the usually value (180°).

     

The Gallides SrRh2Ga2, SrIr2Ga2, and Sr3Ir4Ga4

The gallides SrRh₂Ga₂, SrIr₂Ga₂, and Sr₃Rh₄Ga₄ were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single‐crystal X‐ray diffraction: CaRh₂B₂ type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR₂ = 0.0218, 398 F² values, 15 variables for SrRh₂Ga₂; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr₂Ga₂, and Na₃Pt₄Ge₄ type, I$\bar{4}$ 3m, a = 777.4(2) pm, wR₂ = 0.0234, 190 F² values, 11 variables for Sr₃Ir₄Ga₄. The gallides SrRh₂Ga₂ and Sr₃Ir₄Ga₄ exhibit complex, covalently bonded three‐dimensional [Rh₂Ga₂] and [Ir₄Ga₄] networks with short Rh–Ga (241–246 pm) and Ir–Ga (243–259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh₂Ga₂ and by 4 Ir + 8 Ga in Sr₃Ir₄Ga₄. The structure of SrRh₂Ga₂ is discussed along with the monoclinic distortion variants HoNi₂B₂ and BaPt₂Ga₂ on the basis of a group‐subgroup scheme.     

Heterometallic integer-spin analogues of S = 9/2 Mn4 cubane single-molecule magnets

A family of distorted heterometallic cubanes, [Mn (III) 3Ni (II)(hmp) 3O(N 3) 3(O 2CR) 3], where O 2CR (-) is benzoate ( 1), 3-phenylpropionate ( 2), 1-adamantanecarboxylate ( 3), or acetate ( 4) and hmp (-) is the anion of 2-pyridinemethanol, was synthesized and structurally as well as magnetically characterized. These complexes have a distorted-cubane core structure similar to that found in the S = 9/2 Mn 4 cubane family of complexes. Complexes 1, 3, and 4 crystallize in rhombohedral, hexagonal, and cubic space groups, respectively, and have C 3 molecular symmetry, while complex 2 crystallizes in the monoclinic space group Cc with local C 1 symmetry. Magnetic susceptibility and magnetization hysteresis measurements and high-frequency electron paramagnetic resonance (HFEPR) spectroscopy established that complexes 1-4 have S = 5 spin ground states with axial zero-field splitting (ZFS) parameters ( D) ranging from -0.20 to -0.33 cm (-1). Magnetization versus direct-current field sweeps below 1.1 K revealed hysteresis loops with magnetization relaxation, definitely indicating that complexes 1-4 are single-molecule magnets that exhibit quantum tunneling of magnetization (QTM) through an anisotropy barrier. Complex 2 exhibits the smallest coercive field and fastest magnetization tunneling rate, suggesting a significant rhombic ZFS parameter ( E), as expected from the low C 1 symmetry. This was confirmed by HFEPR spectroscopy studies on single crystals that gave the following parameter values for complex 2: gz = 1.98, gx = gy = 1.95, D = -0.17 cm (-1), B 4 (0) = -6.68 x 10 (-5) cm (-1), E = 6.68 x 10 (-3) cm (-1), and B 4 (2) = -1.00 x 10 (-4) cm (-1). Single-crystal HFEPR data for complex 1 gave g z = 2.02, gx = gy = 1.95, D = -0.23 cm (-1), and B 4 (0) = -5.68 x 10 (-5) cm (-1), in keeping with the C 3 site symmetry of this Mn 3Ni complex. The combined results highlight the importance of spin-parity effects and molecular symmetry, which determine the QTM rates.     

Can the Hole Liquid Undergo Wigner Crystallization in High-Tc La2-x Sr x CuO4 at Low Density?

Abstract

A microscopic interpretation is proposed for the behaviour of the superconducting transition temperature T_c as a function of hole concentration p in La_2-x Sr _x CuO₄ when oxygen vacancies are suppressed. At high p ～ 0.32 a BCS-type formula for T_c is assumed, whereas at low p ～ 0.06 it is proposed that the holes undergo Wigner crystallization. Near the Wigner transition, one has a strongly correlated hole liquid, and Cooper pair binding will become increasingly difficult as p → 0.06 from above, because the Fermi distribution is strongly changed from the unit step function, appropriate near p ～ 0.32. Some experiments are proposed to test the microscopic model put forward here.