Syntheses,crystal structures,and properties of nickel and cadmium complexes containing imidazole derivatives

[Ni₃(C₁₃H₉N₂O)₅(CH₃OH)₂] (1) and [Cd(C₁₂H₈N₃)₃] (2) were synthesized in methanol and characterized by elemental analyses, IR spectra, and X-ray diffraction. Complex 1 is trinuclear with three unsymmetric Ni(II)'s having different coordinated environments bridged by four oxygen atoms from five ligands. Intermolecular antiferromagnetic interactions were observed in 1. Complex 2 is mononuclear with Cd(II) six-coordinate by six nitrogen atoms from three bidentate HPBM anions. Complex 2 shows emission maxima in the blue region.     

The Heusler phases LiRh2Si and LiRh2Ge: Synthesis, structure and properties

The isostructural Heusler phases LiRh₂Si and LiRh₂Ge have been synthesized from the elements and an excess of lithium at 1000 °C. Both materials adopt the CuMn₂Al crystal structure, space group Fm−3m (No. 225) with the room temperature lattice parameter a=5.747(1) Å [Vol=189.866(1) Å³] and a=5.847(1) Å [Vol=199.88(6) Å³] for LiRh₂Si and LiRh₂Ge, respectively. X-ray analyses suggest mixed site occupancy of the form Li_1−xRh₂Si_1+x (x<0.4), but not for LiRh₂Ge. Both materials are diamagnetic, χ_mol(LiRh₂Si)=−6×10⁻⁵ cm³(mole)⁻¹ and χ_mol(LiRh₂Ge)=−10×10⁻⁵ cm³(mole)⁻¹ and metallic with room temperature resistivities of approximately 19 and 32 μΩ cm, respectively. These properties are consistent with the calculated electronic structure.     

Structure and physical properties of nonstoichiometric rare-earth cadmium antimonides, RECd1−xSb2 (RE=La, Ce, Pr, Nd, Sm)

The ternary rare-earth cadmium antimonides RECd_1−xSb₂ (RE=La, Ce, Pr, Nd, Sm) were prepared by reaction of the elements at 1000 °C. The presence of Cd defects, previously found for LaCd_0.700(5)Sb₂ and CeCd_0.660(4)Sb₂, has been confirmed by single-crystal X-ray diffraction studies for the isotypic compounds PrCd_0.665(3)Sb₂, ), NdCd_0.659(3)Sb₂, ), and SmCd_0.648(3)Sb₂, ). These compounds adopt the HfCuSi₂-type structure (Pearson symbol tP8, space group P4/nmm, Z=2). The electrical and magnetic properties of samples with nominal composition RECd_0.7Sb₂ were investigated. All exhibit metallic behaviour, but CeCd_0.7Sb₂ undergoes an abrupt drop in its electrical resistivity below 3 K. LaCd_0.7Sb₂ exhibits temperature-independent Pauli paramagnetism and SmCd_0.7Sb₂ displays van Vleck paramagnetism. The remaining compounds obey the modified Curie-Weiss law at high temperatures. CeCd_0.7Sb₂ undergoes ferromagnetic ordering below 3 K, reaching a saturation magnetization of ∼1.0 μ_B, whereas PrCd_0.7Sb₂ and NdCd_0.7Sb₂ remain paramagnetic down to 2 K.     

Strukturchemische und magnetische Untersuchungen an Ho3+‐β″‐Al2O3(Ho0, 5Mg0, 5Al10, 5O17)

Structural Chemistry and Magnetic Properties of Ho³⁺‐β″‐Al₂O₃(Ho_{0, 5}Mg_{0, 5}Al_{10, 5}O₁₇) The crystal structure of Ho³⁺‐β″‐Al₂O₃(Ho_{0, 5}Mg_{0, 5}Al_{10, 5}O₁₇) was determined by single crystal X‐ray diffraction methods at room temperature (trigonal, R3¯m, Z = 3, a = 561.43(12) pm, c = 3353.7(11) pm). The structural chemical results are correlated with magnetic measurements, where ligand field calculations applying the angular overlap model have been taken into account.     

CaRhIn with TiNiSi Type Structure and CaTIn2 (T = Rh,Ir) with a New Filled Version of the Zintl Phase CaIn2

CaRhIn, CaRhIn₂, and CaIrIn₂ were synthesized by reacting the elements in glassy carbon crucibles under an argon atmosphere in a high‐frequency furnace. CaRhIn adopts the TiNiSi structure: Pnma, a = 730.0(4) pm, b = 433.1(2) pm, c = 828.8(4) pm, wR2 = 0.0707, 630 F² values, 20 variables. The CaRhIn structure consists of strongly puckered Rh₃In₃ hexagons with Rh–In distances ranging from 273 to 276 pm. Due to the strong puckering each rhodium atom has a distorted tetrahedral indium environment. The calcium atoms fill the channels within the three‐dimensional [RhIn] polyanion. CaRhIn₂ and CaIrIn₂ crystallize with a new structure type: Pnma, a = 1586.2(3) pm, b = 781.4(2) pm, c = 570.9(1) pm, wR2 = 0.0385, 1699 F² values, 44 variables for CaRhIn₂, and Pnma, a = 1588.7(3) pm, b = 780.8(1) pm, c = 574.0(1) pm, wR2 = 0.0475, 1661 F² values, 44 variables for CaIrIn₂. The structures of CaRhIn₂ and CaIrIn₂ can be described as an orthorhombically distorted rhodium respectively iridium filled CaIn₂. The motif of transition metal filling is similar to that found in MgCuAl₂ type compounds CaTIn₂ (T = Pd, Pt, Au) and SrTIn₂ (T = Rh, Pd, Ir, Pt), but constitute a different tiling. Semi‐empirical band structure calculations for CaRhIn and CaRhIn₂ reveal strong bonding In–In and Rh–In but weaker Ca–Rh and Ca–In interactions. Magnetic susceptibility and resistivity measurements of compact polycrystalline samples of CaRhIn₂ indicate weak Pauli paramagnetism and metallic conductivity with a room temperature value for the specific resistivity of 230 ± 50 μΩcm.     

Effect of Strain on the Electronic Structure and Phonon Stability of SrBaSn Half Heusler Alloy

This paper presents the strain effects on the structural, electronic and phonon properties of a newly proposed SrBaSn half Heusler compound. Since it is stable considering chemical thermodynamics, we tested its strength against uniform strain w.r.t phonon spectrum and it produces a direct bandgap of 0.7 eV. The direct bandgap reduces to 0.19 eV at −12% strain beyond which the structure is unstable. However, an indirect gap of 0.63 eV to 0.39 eV is observed in the range of +5% to +8% strain and afterwards the strain application destabilizes the structure. From elastic parameters, the ductile nature of this material is observed.     

Synthesis and structural characterization of 2D Zn(II), Cd(II), and Co(II) coordination polymers containing 3-chloro-1,2-benzenedicarboxylate and positional isomers of triazole-bipyridine

Three compounds, [Zn₂L₂(4,4′-bpt)₂] _n (1), [Cd₂L₂(3,4′-bpt)(H₂O)₂] _n (2) and {[CoL(3,3′-bpt)(H₂O)]?H₂O} _n (3) (L?=?3-Cl-1,2-benzenedicarboxylate dianion, 4,4′-bpt?=?1H-3,5-bs(4-pyridyl)-1,2,4-itriazole, 3,4′-bpt?=?1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole and 3,3′-bpt?=?1H-3,5-bis(3-pyridyl)-1,2,4-triazole), based on three positionally isomeric triazole-bipyridine ligands, were synthesized. Structural analyses of 1–3 reveal diverse 2-D network structures, which are based on different [ML] _n (M?=?Zn, Cd, Co) chains. In the [ZnL] _n chains of 1, the carboxylic groups of L connect the adjacent Zn(II) centers with a monodentate bridging coordination mode (μ₂-η^{1 ?}/^? η¹ ). In 2, [CdL] _n is a double chain connected by the carboxylic groups of L with μ₃-η^{1 ?}/^? η²/η² and μ₃-η^{1 ?}/^? η^{1 ?}/^? η² bridges. The [CoL] _n chains of 3 are formed by the carboxylic groups of L with the μ₂-η^{1 ?}/^? η² coordination mode. The powder X-ray diffraction and the thermal stability of 1–3, the luminescent properties of 1 and 2, and the magnetic behavior of 3 have been briefly investigated.     

High‐TC Ferromagnetic Semiconductor‐Like Behavior and Unusual Electrical Properties in Compounds with a 2×2×2 Superstructure of the Half‐Heusler Phase

Heusler phases, including the full‐ and half‐Heusler families, represent an outstanding class of multifunctional materials on account of their great tunability in compositions, valence electron counts (VEC), and properties. Here we demonstrate a systematic design of a series of new compounds with a 2×2×2 superstructure of the half‐Heusler unit cell in X–Y–Z (X=Fe, Ru, Co, Rh, Ir; Y=Zn, Mn; Z=Sn, Sb) systems. Their structures were solved by using both powder and single‐crystal X‐ray diffraction, and also directly observed by using high‐angle annular dark‐field imaging in a scanning transmission electron microscope (HAADF‐STEM). The VEC values of these new compounds span a wide and continuous range comparable to those for the full‐ and half‐Heusler families, thereby implying tunability in compositions and physical properties in the superstructure. In fact, we observed abnormal electrical properties and a ferromagnetic semiconductor‐like behavior with a high and tunable Curie temperature in these superstructures.     

Structure and physical properties of rare-earth zinc antimonides REZn1-xSb2 (RE=La, Ce, Pr, Nd, Sm, Gd, Tb)

The ternary rare-earth zinc antimonides REZn_1-xSb₂ (RE=La, Ce, Pr, Nd, Sm, Gd, Tb) were prepared by heating at 1050 °C followed by annealing at 600 °C. For all members, single-crystal X-ray diffraction studies indicated that the Zn deficiency is essentially fixed, corresponding to the formula REZn_0.6Sb₂, with no appreciable homogeneity range. These compounds adopt the HfCuSi₂-type structure (Pearson symbol tP8, space group P4/nmm, Z=2). Single-crystal electrical resistivity measurements confirmed the occurrence of an abrupt resistivity decrease near 4 K for RE=Ce, and a less pronounced one for RE=La, Pr, and Gd. Except for the ferromagnetic Ce (T_c=2.5 K) and antiferromagnetic Tb (T_N=10 K) members, all remaining compounds exhibit no long-range magnetic ordering down to 2 K, instead showing temperature-independent (RE=La), van Vleck (RE=Sm), or Curie-Weiss paramagnetism (RE=Pr, Nd, Gd).     

Synthesis,Crystal Structure,and Magnetic Properties of a New 2D Twofold Interpenetrated Coordination Polymer [Cu(3,4‐pybz)2]n

A new coordination polymer, [Cu(3, 4‐pybz)₂]_n ( 1 ) [3,4‐Hpybz = 3‐pyridin‐4‐yl‐benzoic acid], was synthesized by hydrothermal reaction of CuCl₂ · 2H₂O and 3,4‐Hpybz, and characterized by elemental analysis, IR spectroscopy, PXRD, and single‐crystal X‐ray diffraction. The structure determination reveals that 1 exhibits a 2D twofold interpenetrated 4‐connected (4,4) network topology, these 2D layers are further enlarged to form the final 3D supramolecular edifice via aromatic π–π stacking interactions. In addition, the magnetic behavior and thermogravimetric analysis of 1 were also studied.     

Two new tetranuclear complexes of the macrocyclic oxamide [MCu3] (M = Cd, Mn, macrocyclic oxamide = 1,4,8,11-tetraazacyclotradecanne-2,3-dione): syntheses, spectra and magnetic properties

Two new tetranuclear complexes of macrocyclic oxamide [Cd(CuL)₃](NO₃)₂·2.5H₂O 1, [Mn(CuL)₃(OH)₂](ClO₄)₂·Mn(H₂O)₆·4.5H₂O 2 (L = 1,4,8,11-tatraazacyclotradecanne-2,3-dione) have been synthesized, structurally characterized and preliminary investigated by magnetic studies. The structures of the title complexes consist of a tetranuclear units MCu₃ (M = Cd, Mn), the packing diagram shows two-dimensional and three-dimensional system through intermolecular weak interactions. The temperature-dependent magnetic susceptibilities of complex 2 were analyzed by an approximate treatment leading to J = −33 cm⁻¹, g_Cu = 2.10, g_Mn = 1.95 indicating antiferromagnetic exchange between Cu(II) and Mn(II) ions.     

Synthesis,crystal structure,and magnetism properties of coordination polymer: Co(2-mpac)2(H2O)2 as molecular building block

Utilizing Co(2-mpac)₂(H₂O)₂ as molecular building block, a coordination polymer, [Co₂(2-mpac)₄(4,4′-bpy) · 2H₂O] _n (1) (2-mpac = 5-methyl-2-pyrazinecarboxylic acid; 4,4′-bpy = 4,4′-bipyridine), was synthesized and structurally characterized by X-ray single crystal diffraction. Elemental analysis, infrared, and magnetism are presented. Variable temperature magnetic susceptibility measurements exhibit weak antiferromagnetic interaction between Co centers in 1.     

Three New Lanthanide Coordination Polymers Built from H2bpdc Ligands: Syntheses,Structures, and Properties

Three new lanthanide‐organic coordination polymers, {[Ln₂(bpdc)₂(H₂O)₆(NO₃)] · NO₃} [Ln = La ( 1 ), Ce ( 2 ), Pr ( 3 )] (H₂bpdc = 2, 2′‐bipyridine‐6, 6′‐dicarboxylic acid) were synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR spectroscopy as well as single‐crystal and powder X‐ray diffraction. Single‐crystal X‐ray diffraction analysis revealed that compounds 1 – 3 are isostructural, composed of two dimensional honeycomb network linked by bpdc ligands. The magnetic property of compound 3 was investigated.     

Ternary Rare Earth (RE) Gold Compounds REAuCd and RE2Au2Cd

New intermetallic rare earth compounds REAuCd (RE = Y, La–Nd, Sm–Yb) and RE₂Au₂Cd (RE = La, Pr, Nd, Sm) were prepared by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. The equiatomic REAuCd compounds with RE = Y, La–Nd, Sm, and Gd–Tm adopt the ZrNiAl type structure with space group P62m. Single crystal X‐ray data yielded a = 786.2(2), c = 415.9(1) pm, wR2 = 0.0337, 402 F² values for LaAuCd and a = 782.91(9), c = 410.01(5) pm, wR2 = 0.0653, 395 F² values for CeAuCd with 14 parameters for each refinement. Geometrical motifs in CeAuCd are two types of gold centered tricapped trigonal prisms: [Au1Cd₃Ce₆] and [Au2Cd₆Ce₃]. The gold and cadmium atoms form a three‐dimensional [AuCd] polyanion in which the cerium atoms fill distorted hexagonal channels. EuAuCd and YbAuCd crystallize with a TiNiSi type structure, space group Pnma: a = 755.2(1), b = 450.59(5), c = 878.6(1) pm, wR2 = 0.0904, 500 F² values for EuAuCd, and a = 731.64(3), b = 432.94(2), c = 875.80(4) pm, wR2 = 0.1192, 457 F² values for YbAuCd with 20 parameters for each refinement. In these structures the europium(ytterbium) and cadmium atoms form zig‐zag chains of egde‐ and face‐sharing trigonal prisms which are centered by the gold atoms. Also in EuAuCd and YbAuCd a three‐dimensional [AuCd] polyanion occurs in which the europium(ytterbium) atoms are embedded. Europium and ytterbium are divalent in EuAuCd and YbAuCd. Susceptibility measurements show Pauli paramagnetism for YbAuCd and Curie‐Weiss behavior above 100 K for EuAuCd with an experimental magnetic moment of 7.86(6) μ_B/Eu. Ferromagnetic ordering is detected at 28 K. The saturation magnetic moment is 7.1(1) μ_B/Eu at 1.9 K. ¹⁵¹Eu Mössbauer spectra show an isomer shift of –9.2(2) mm/s and full magnetic hyperfine field splitting at 4.2 K with an internal hyperfine field of 19.5(4) T at the europium nuclei. The RE₂Au₂Cd compounds crystallize with the Mo₂FeB₂ structure, a ternary ordered version of the U₃Si₂ type. These structures may be considered as an intergrowth of distorted CsCl and AlB₂ related slabs of compositions RECd and REAu₂. Chemical bonding in REAuCd and RE₂Au₂Cd is briefly discussed.     

Synthesis,Crystal Structure and Properties of RbMnO2

RbMnO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursers (Mn₂O₃, RbN₃ and RbNO₃) were heated in a special regime up to 600 °C and annealed at this temperature for 30 h in specially designed silver crucibles. Single crystals have been grown by annealing a 1:1 mixture of Rb₂O and MnO_x at 585 °C for 1200 h. According to the crystal structure determination Mn³⁺ is in a square‐pyramidal coordination by oxygen. These [MnO₅] units form double chains extending along the crystallographic c‐axis. RbMnO₂ shows Curie‐Weiss behaviour down to ～ 100 K. A fit of the susceptibility data yields an average value of the magnetic moment (per manganese atom) of μ_eff = 5.33 μ_B, and θ_p = –820 K. At 50 K and low field strength onset of ferromagnetic order due to spin canting has been observed.     

Structural, electronic and elastic properties of MAX phases M2GaN (M = Ti, V and Cr)

Based on first-principles total energy calculations, we have investigated the systematic trends for structural, electronic and elastic properties of the MAX phases M₂GaN depending on the type of M transition metal (M are Ti, V and Cr). The optimized zero pressure geometrical parameters: the two unit cell lengths (a, c), the internal coordinate z and the bulk modulus are calculated. The results for the lattice constants are in agreement with the available experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site-projected l-decomposed density of states shows that bonding is due to M d-N p and M d-Ga p hybridizations. The elastic constants are calculated using the static finite strain technique. The shear modulus C₄₄, which is directly related to the hardness, reaches its maximum when the valence electron concentration is in the range 10.5–11.0. The isotropic elastic moduli, namely, bulk modulus (B), shear modulus (G), Young's modulus (E) and Poisson's ratio (σ) are calculated in framework of the Voigt–Reuss–Hill approximation for ideal polycrystalline M₂GaN aggregates. We estimated the Debye temperature of M₂GaN from the average sound velocity. This is the first quantitative theoretical prediction of the electronic structures, and elastic constants and related properties for Ti₂GaN, V₂GaN and Cr₂GaN compounds that require experimental confirmation.     

CsTi2Cl7‐II: Synthese,Kristallstruktur und magnetische Eigenschaften

CsTi₂Cl₇‐II: Synthesis, Crystal Structure, and Magnetic Properties Single crystals of a second modification of CsTi₂Cl₇ (II) were obtained from the reaction of CsCl with TiCl₂ and C₆Cl₆ (monoclinic, P2₁/m (No. 11), Z = 2, a = 635.4(3), b = 1163.0(2), c = 728.0(2) pm, β = 91.49(4)°). X‐ray pure powder samples are obtained from the binary components in 1 : 2 molar mixtures of CsCl and TiCl₃ (melting at 900 °C and annealing at 550 °C below the melting point). The crystal structure of CsTi₂Cl₇‐II contains layers of densest packings of spheres of the compositions CsCl₃ and Cl₄, respectively, that are stacked alternatively in the [010] direction according to the sequence … ABAC … Ti³⁺ resides in one quarter of the octahedral holes between these layers in a way that confacial bioctahedra are connected via two common edges forming a zigzag chain running parallel to [010]. This structure with Ti³⁺–Ti³⁺ distances of 323 and 347 pm, respectively, is reflected in the antiferromagnetic behavior with interactions about sixteen times stronger within the dimers than between them (J = –490 cm^–1 bzw. J = –30 cm^–1).