- Giant Negative Magnetoresistance in GdI2: Prediction and Realization
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The electronic structure of the layered d1 compound GdI2 has been examined systematically in view of its relation to other layered d1 systems including superconducting and isostructural 2H-TaS2 and 2H-NbSe2. A van Hove type instability is evident in suitable representations of the Fermi surface. The presence of the half-filled and magnetic 4f level should preclude the possibility of superconductivity. Instead GdI2 orders ferromagnetically at 290(5) K and displays large negative magnetoresistance ≈70% at 7 T close to room temperature. This finding provides support to the idea that materials can be searched rationally for interesting properties through high level electronic structure calculations.
- Felser,Ahn,Kremer,Seshadri,Simon
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- Gd7I12Zn: A group 12 atom in the octahedral Gd 6 cluster
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The title compound was synthesized from Gd, GdI3 and Zn under Ar atmosphere at 850°C. It crystallizes in the space group R3 (No. 148) with lattice constants a = 15.686(1) A and c = 10.4882(8) A. The structure features isolated Zn-centered Gd6 octahedra with all edges and corners capped by I atoms. The disorder of the Gd atoms is rationalized via electron microscopic techniques. A computational analysis using the extended Hueckel method has been carried out in order to understand the bonding of this compound. The structure of isotypic La7I12Co is also remarked (a = 16.040(1) A and c = 10.905(2) A).
- Lukachuk, Mar'yana,Kienle, Lorenz,Zheng, Chong,Mattausch, Hansjuergen,Simon, Arndt
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- Gd10I16(C2)2 and Gd10Br15B2/Tb10Br15B 2 cluster compounds with M10 twin octahedra
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The compound Gd10I16(C2)2 can be prepared from Gd metal, GdI3 and C at 950 °C. It crystallizes in P1? with a = 10.463(4) A?, b = 16.945(6) A?, c = 11.220(4) A?, α = 99.15(3)°, β = 92.68(3)° und γ = 88.06(3)°. Gd10Br15B2 is formed between 900 und 950 °C, Tb10Br15B2 between 900 und 930 °C from stoichiometric amounts of the rare earth metals, tribromide and boron. Both compounds crystallize in the space group P1? for Gd10Br15B2 with a = 8.984(2) A?, b = 9.816(2) A?, c = 10.552(5) A?, α = 91.14(3)°, β = 114.61(3)° and γ = 110.94(3)° and for Tb10Br15B2 with a = 8.939(4) A?, b = 9.788(3) A?, c = 10.502(2) A?, α = 91.19(3)°, β = 114.51(3)° and γ = 111.10(2)°. In the crystal structures of all three compounds the rare earth metals form edge-shared Ln10 twin octahedra. In Gd10I16(C2)2 the Gd octahedra are centered with C2 groups (dC-C = 1.43(7) A?). In Ln10Br15B2 (Ln = Gd, Tb) the octahedra contain single boron atoms. The clusters are connected through halide atoms to chains [Ln10(Z)2Xi4Xi-i 4/2Xi-a2]. Adjacent chains are fused threedimensionally via Ii-a2Ii-a6 for the Gd iodide carbide and via Bri-i2/2Bri-a6 for the bromide borides of Gd und Tb. It is interesting to see an identical pattern of connection between the chains for the reduced oxomolybdates, e. g. PbMo5O8.
- Mattausch, Hansju?rgen,Warkentin, Eberhard,Oeckler, Oliver,Simon, Arndt
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- The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties
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The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI3 and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln12(C2)3I17-type compounds (C 2/c, a=19.610(1) and 19.574(4) A, b=12.406(2) and 12.393(3) A, c=19.062(5) and 19.003(5) A, β=90.45(3)° and 90.41(3)°, for Pr12(C2)3I17 and Nd12(C2)3I17, respectively). All compounds contain infinite zigzag chains of C2-centered metal atom octahedra condensed by edge-sharing into the [tcc]∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd12(C2)3I17 sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln3+)12(C26-)3(I-)17(e-) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd12(C2)3I17, Gd12(C2)3I17 and Dy12(C2)3I17 indicate the coexistence of competing magnetic interactions leading to spin freezing at Tf=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at TN=25 and 29 K, respectively. For Dy12(C2)3I17, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.
- Ryazanov, Mikhail,Mattausch, Hansjuergen,Simon, Arndt
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- From an impurity to the pure compound - An electron microscopy study
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The power of electron microscopy techniques for the determination of structure and composition of marginal byproducts is demonstrated for rare earth metal cluster compounds. Small amounts of the new phase Gd4GaI 6 in samples with the nominal composition Gd7GaI 12 could only be identified by a combined approach of EDX, electron diffraction and HRTEM. The structure of Gd4GaI6 can be assigned to the Y4BBr6-type containing chains of Gd 6 octahedra which are centered by Ga atoms. The results of the electron microscopy study initiated the synthesis of homogeneous samples of the new compound Gd4GaI6 by applying the correct ratio of the starting materials.
- Kienle,Lukachuk,Duppel,Mattausch,Simon
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- Ferromagnetic coupling in hexanuclear gadolinium clusters
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The magnetic susceptibilities of hexanuclear gadolinium clusters in the compounds Gd(Gd6Zl12) (Z = Co, Fe, or Mn) and CsGd(Gd 6Col12)2 are reported and subjected to theoretical analysis with the help of density functional theory (DFT) computations. The single-crystal structure of Gd(Gd6Col12) is reported here as well. We find that the compound with a closed shell of cluster bonding electrons, Gd(Gd6Col12), exhibits the effects of antiferromagnetic coupling over the entire range of temperatures measured (4-300 K). Clusters with unpaired, delocalized cluster bonding electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic coupling, except at lower temperatures (less than 30 K) where intercluster antiferromagnetic coupling suppresses the susceptibilities. The presence of two unpaired CBEs, as in [Gd6Mnl12] 3-, yields stronger coupling than when just one unpaired CBE is present, as in [Gd6Fel12]3- or [Gd 6Col12]2-. DFT calculations on model molecular systems, [Gd6Col12](OPH3)6 and [Gd6Col12]2(OPH3)10, indicate that the delocalized cluster bonding electrons are highly effective at mediating intracluster ferromagnetic exchange coupling between the Gd atom 4f7 moments and that intercluster coupling is expected to be antiferromagnetic. The DFT calculations were used to calculate the relative energies of various 4f7 spin patterns and form the basis for construction of a simple spin Hamiltonian describing the coupling within the [Gd6Col12] cluster.
- Sweet, Lucas E.,Roy, Lindsay E.,Meng, Fanqin,Hughbanks, Timothy
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- Structural characterization of methanol substituted lanthanum halides
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The first study into the alcohol solvation of lanthanum halide [LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(μ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H2O)7(MeOH)2](Br)3 (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH2, crystals of [Ca(MeOH)6](Br)2 (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr2.75·5.25(MeOH)]+0.25 [LaBr3.25·4.75(MeOH)]-0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr3 in MeOH forming the 8-coordinated [LaBr3(MeOH)5] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX3 derivatives were isolated as [(MeOH)4(Cl)2La(μ-Cl)]2 (6) and [La(MeOH)9](I)3·MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR (139La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4-6 were slightly higher in comparison to their hydrated counterparts.
- Boyle, Timothy J.,Ottley, Leigh Anna M.,Alam, Todd M.,Rodriguez, Mark A.,Yang, Pin,Mcintyre, Sarah K.
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p. 1784 - 1795
(2010/07/03)
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- RE19(C2)3i34 (RE = Y, Gd): Compounds with discrete RE6I12 clusters and isolated RE atoms
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The compounds RE19(C2)3I34 (RE = Y, Gd) were prepared from RE, REI3 and carbon in a molar ratio of 20:34:18 by the addition of three parts of REH at 920 °C (Y) and 900 °C (Gd), respectively, forming moisture sensitive, black shiny brittle polyhedra. X-ray single crystal investigations indicated the triclinic system and E value statistics showed P1, a = 9.3683(9) , b = 10.3410(9) A, c = 22.1726(20) A, α = 79.104( 10)°, β = 88.175( 11 )°, γ = 69.227( 10)° for Y19(C2)3I 34 and a = 9.4172(9) A, b = 10.3390(10) A c= 22.3711(24) A, α= 79.001(12)°, β= 88.320(12)°, γ = 69.250(11)° for Gd19(C2)3I34,, respectively. The RE atoms form two sets of different RE6 octahedra centered by C2 groups, which are coordinated by iodine atoms above all edges. In addition one isolated RE position occurs. The refinement served problems because of significant disorder showing up in a 65 % occupation of the isolated RE position and quite significant residual electron densities near the heavy atom positions. Electron diffraction confirmed the ideal structure, however, a detailed analysis via HRTEM showed alternations in the sequence of two kinds of layers.
- Schaloske, Manuel C.,Kienle, Lorenz,Duppel, Viola,Mattausch, Hansjuergen,Simon, Arndt
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p. 188 - 195
(2010/06/12)
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- New layered germanide halides RE2GeX2 (RE = Y, Gd; X = Br, I)
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The title compounds were synthesized from RE, REX3, and Ge under an Ar atmosphere at 1200-1370 K. Y2GeI2 and Gd 2GeI2 crystallize in space group R3m with lattice constants a = 4.2135(3) and 4.2527(1) A and c = 31.480(2) and 31.657(1) A, respectively. Gd2GeBr2 crystallizes in two modifications, the 1T-type (space group P3m1; a = 4.1668(2) A, c = 9.8173(6) A) and the 3R-type (space group R3m; a = 4.1442(9) A, c = 29.487(7) A). The structural motifs of RE2GeX2 compounds are Ge-centered slightly distorted RE6 octahedra connected via their common edges and extending in the a and b directions. The resulting close-packed double layers are separated by halogen atoms. The electrical resistivity measurements revealed semiconductor behavior for Y 2GeI2 and Gd2GeI2 and a metal-semiconductor transition for 1T-Gd2GeBr2. Magnetic susceptibility and heat capacity measurements show long-range magnetic ordering for Gd2GeI2 and 1T-Gd2GeBr2 at ~15 and ~13 K, respectively.
- Lukachuk, Mar'yana,Kremer, Reinhard K.,Mattausch, Hansjuergen,Simon, Arndt
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p. 3231 - 3235
(2008/10/09)
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- RE2+xI2M2+y (RE = Ce, Gd, Y; M = Al, Ga): Reduced rare earth halides with a hexagonal metal atom network
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The title compounds were synthesized from RE, REI3 (RE = Ce, Gd, Y) and Al or Ga under an Ar atmosphere at 930-950 °C. The non-stoichiometric Ce2+xI2Al2+y and Ce 2+xI2Ga2+y compounds crystallize in the space group R3?m (No. 166) with lattice constants a = 4.3645(3), c = 35.914(2) A? for the Al and a = 4.3009(2), c = 35.680(4) A? for the Ga compound. Excess electron density found in the Wyckoff position 3a could be due to a fractional occupation by Ce or M (x = 0.06, y = 0 or x = 0, y = 0.11 in the case of the Ga_compound). The stoichiometric Gd2I2Ga 2 and Y2I2Ga2 compounds crystallize in the space group P3?m1 (No. 164) with lattice constants a = 4.1964(1) and 4.1786(7) A?, c = 11.4753(4) and 11.434(2) A?, respectively. Their structures feature M-centered (M = Al, Ga) RE trigonal prisms condensed via common rectangular faces. The electronic origin of the surplus of metal atoms in the octahedral voids between the I-layers of the Ce compounds was explored via extended Huckel-type calculations. Magnetic susceptibility, electrical resistivity and heat capacity measurements have also been carried out. These reveal a metal-insulator transition of Gd2I2Ga2 at 40 K.
- Lukachuk, Mar'yana,Zheng, Chong,Mattausch, Hansjürgen,Banks, Michael G.,Kremer, Reinhard K.,Simon, Arndt
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p. 633 - 641
(2008/09/21)
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- On the reactivity of lanthanide iodides LnIx (x < 3) formed in the reactions of lanthanide metals with iodine
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The reduced lanthanide iodides of the composition LnIx (Ln = Sc, Y, La, Ce, Pr, Gd, Ho, and Er; x 3) were obtained by the reaction of an excess of the appropriate metal with iodine at high temperatures. The diamagnetism of the Sc, Y, and La d
- Khoroshenkov,Petrovskaya,Fedushkin,Bochkarev
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p. 699 - 702
(2008/10/08)
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- Rare earth iodide complexes of 4-formyl-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one
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Rare earth complexes of 4-formyl-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one (FDPP) having the general formula [Ln(FDPP)4I2]I, where Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho and Er, have been synthesised and characterised by elemental analyses, molar conductance in non-aqueous solvents, electronic, infrared and proton NMR spectra as well as thermogravimetric analyses. FDPP acts as a neutral monodentate ligand coordinating through the ring carbonyl oxygen. Two of the iodide ions are coordinated. A coordination number of six may be assigned to the metal ion in these complexes. The covalency parameters evaluated from the solid state electronic spectra suggest weak covalent character of the metal-ligand bond. The TG data of the lanthanum complex indicate that the complex is stable up to about 140° C and undergoes decomposition in three stages forming lanthanum oxide as the final product.
- Joseph, Siby,Radhakrishnan
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p. 1219 - 1229
(2008/10/09)
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- Planar B4 rhomboids: The rare earth boride halides RE4X5B4
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The new compounds RE4X5B4 (RE = La, Ce, Pr, Gd and X = Br, I) and RE4I5B2C (RE = La, Ce) are prepared via the reaction of RE metal, REX3 and B, or B and C at temperatures 1670 ≥ T ≥ 1270 K in welded tantalum ampoules. Chains of interconnected B4 rhomboids are the characteristic features of the crystal structures. According to band structure calculations, the compounds are one-dimensional metals which undergo a gradual metal-to-semiconductor transition at low temperature as experimentally indicated by the steep inrease of electrical resistivity.
- Mattausch,Simon,Felser
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p. 9951 - 9957
(2007/10/03)
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- The standard enthalpy of formation of crystalline gadolinium triiodide
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The enthalpies of the reactions of Gd(cryst.), GdI3(cryst.), KCl(cryst.), KI(cryst.), and H2O(liq.) with HCl.54.38H2O solution were measured in a solution calorimeter with an isothermal jacket from the LKB-8700 apparatus. ΔfH0 (GdI3, cryst., 298.15 K) = -615.7 +/- 1.1 kJ mol-1 was calculated from the results.
- Furkalyuk, M. Yu.,Efimov, M. E.,Goryushkin, V. F.
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p. 587 - 589
(2007/10/02)
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