Curie-Weiss Law Behavior Research Articles

Zinc(II) and copper(II) complexes with benzothiadiazole Schiff-base ligands

The ligand (2-[4-(2,1,3-benzothiadiazole)imino]methyl-phenol) HL1 containing the electron poor benzothiadiazole (BTD) unit, conveniently prepared by condensation of 4-amino-2,1,3-benzothiadiazole and salicylaldehyde, has been structurally characterized by single crystal X-ray diffraction. Two energy minima have been determined, by DFT calculations, for HL1 and for its ortho-vanillin analogue HL2, corresponding either to the conformer observed in the solid state or to the chelating tridentate form. TD-DFT calculations have been performed on HL1 and HL2 in order to assign their experimental UV–visible absorption bands. Reaction of HL1 and HL2 with copper (II) hexafluoroacetylacetonate (hfac), zinc (II) hexafluoroacetylacetonate or zinc (II) acetate provided the neutral complexes [Cu(L1)(hfac)] (1), [Zn(L1)2] (2), [Cu(L2)2] (3) and [Zn(L2)2] (4) which were structurally characterized, with a focus on the coordination sphere of the metal centre and on the intermolecular interactions. The UV–visible absorption properties of the Zn(II) complexes 2 and 4 have been experimentally and theoretically investigated and compared to those of the ligands. Finally, the cryomagnetic study of 1 and 3 in the temperature range 2.0–295.0 K reveals a Curie-Weiss law behaviour with very weak intermolecular antiferromagnetic interactions in the low temperature region.

Absence of superconductivity in LiPdHx

Theoretical calculations about LiPdH predict that it may be a superconductor. Using the high-pressure synthesis technique up to 3 GPa, we have successfully fabricated the LiPdH compound. The sample looks quite pure judging from the refinement of the X-ray diffraction pattern. However, no superconductivity has been detected down to about 2 K. The specific heat measurement shows a small Sommerfeld constant = 1.22 mJ mol K, which is a bit smaller than the theoretically predicted value. The magnetic susceptibility measured at 1 Tesla reveals a Curie–Weiss law behaviour in the low-temperature region with an estimate of the magnetic moment of 0.08 /Pd. The temperature dependence of resistivity has also been measured up to 25.2 GPa, but superconductivity is still not observed above 2 K. The large residual resistivity and small residual-resistivity ratio suggest that the quasiparticle scattering by impurities is quite strong, which might be induced by the hydrogen deficiency, and intimately hinders the occurrence of superconductivity in LiPdH.

Flux growth of Yb(6.6)Ir(6)Sn(16) having mixed-valent ytterbium.

The compound Yb6.6Ir6Sn16 was obtained as single crystals in high yield from the reaction of Yb with Ir and Sn run in excess indium. Single-crystal X-ray diffraction analysis shows that Yb6.6Ir6Sn16 crystallizes in the tetragonal space group P42/nmc with a = b = 9.7105(7) Å and c = 13.7183(11) Å. The crystal structure is composed of a [Ir6Sn16] polyanionic network with cages in which the Yb atoms are embedded. The Yb sublattice features extensive vacancies on one crystallographic site. Magnetic susceptibility measurements on single crystals indicate Curie-Weiss law behavior <100 K with no magnetic ordering down to 2 K. The magnetic moment within the linear region (<100 K) is 3.21 μB/Yb, which is ∼70% of the expected value for a free Yb(3+) ion suggesting the presence of mixed-valent ytterbium atoms. X-ray absorption near edge spectroscopy confirms that Yb6.6Ir6Sn16 exhibits mixed valence. Resistivity and heat capacity measurements for Yb6.6Ir6Sn16 indicate non-Fermi liquid metallic behavior.

A Dimeric Copper(II) Complex of Oxalate and Oxamide Dioxime Ligands: Synthesis, Crystal Structure, Thermal Stability, and Magnetic Properties

The dimeric copper(II) complex [Cu(C2O4)(H2oxado)(H2O)]2 (1), where H2oxado=oxamide dioxime, has been synthesized in water and characterized by elemental and thermal analyses, IR spectroscopy, and single-crystal X-ray diffraction. Complex 1 is composed of two neutral [Cu(C2O4)(H2oxado)(H2O)] entities connected by Cu-O bonds between oxalate oxygen atoms and copper(II) ions, thereby producing a centrosymmetric dimer, with the Cu(II) centers exhibiting a strongly distorted octahedral coordination. Neighboring dimers are hydrogen-bonded through O- H···O interactions leading overall to a layer structure. Thermal analyses of complex 1 showed two significant weight losses corresponding to the coordinated water molecules, followed by the decomposition of the network. Variable-temperature (10 - 300 K) magnetic susceptibility measurements revealed very weak antiferromagnetic interactions (θ = 0:86 K from Curie-Weiss law behavior) within the dinuclear unit

Structure and properties of SmCu6 − x In6 + x (x = 0, 1, 2)

High quality single crystals of SmCu6In6 were obtained from the reactions run in excess liquid indium and characterized by means of single crystal X-ray diffraction data. SmCu6In6 crystallizes in the YCu6In6 structure type, tetragonal space group I4/mmm and lattice constants are a = b = 9.2036(3) Å and c = 5.4232(3) Å. SmCu6 − xIn6 + x (x = 0, 1, 2) compounds were obtained using arc melting and characterized using powder X-ray diffraction. Magnetic susceptibility data follow modified Curie–Weiss law behaviour above 50 K and the experimentally measured magnetic moment values in SmCu4In8, SmCu5In7 and SmCu6In6 are 0.83 μ B, 1.45 μ B and 0.90 μ B per Sm atom, respectively. SmCu5In7 and SmCu6In6 compounds show antiferromagnetic ordering at T N = 7.8 K, and no magnetic ordering was observed for SmCu4In8 down to 2 K. Electrical resistivity measurements show that all compounds are of metallic nature.

New Structure Type in the Mixed-Valent Compound YbCu4Ga8

The new compound YbCu(4)Ga(8) was obtained as large single crystals in high yield from reactions run in liquid gallium. Preliminary investigations suggest that YbCu(4)Ga(8) crystallizes in the CeMn(4)Al(8) structure type, tetragonal space group I4/mmm, and lattice constants are a = b = 8.6529(4) Å and c = 5.3976(11) Å. However, a detailed single-crystal XRD revealed a tripling of the c axis and crystallizing in a new structure type with lattice constants of a = b = 8.6529(4) Å and c = 15.465(1) Å. The structural model was further confirmed by neutron diffraction measurements on high-quality single crystal. The crystal structure of YbCu(4)Ga(8) is composed of pseudo-Frank-Kasper cages occupying one ytterbium atom in each ring which are shared through the corner along the ab plane, resulting in a three-dimensional network. The magnetic susceptibility of YbCu(4)Ga(8) investigated in the temperature range 2-300 K showed Curie-Weiss law behavior above 100 K, and the experimentally measured magnetic moment indicates mixed-valent ytterbium. Electrical resistivity measurements show the metallic nature of the compound. At low temperatures, variation of ρ as a function of T indicates a possible Fermi-liquid state at low temperatures.

Crystal Structure of YbCu6In6 and Mixed Valence Behavior of Yb in YbCu6–xIn6+x (x = 0, 1, and 2) Solid Solution

High quality single crystals of YbCu(6)In(6) have been grown using the flux method and characterized by means of single crystal X-ray diffraction data. YbCu(6)In(6) crystallizes in the CeMn(4)Al(8) structure type, tetragonal space group I4/mmm, and the lattice constants are a = b = 9.2200(13) Å and c = 5.3976(11) Å. The crystal structure of YbCu(6)In(6) is composed of pseudo-Frank-Kasper cages filled with one ytterbium atom in each ring. The neighboring cages share corners along [100] and [010] to build the three-dimensional network. YbCu(6-x)In(6+x) (x = 0, 1, and 2) solid solution compounds were obtained from high frequency induction heating and characterized using powder X-ray diffraction. The magnetic susceptibilities of YbCu(6-x)In(6+x) (x = 0, 1, and 2) were investigated in the temperature range 2-300 K and showed Curie-Weiss law behavior above 50 K, and the experimentally measured magnetic moment indicates mixed valent ytterbium. A deviation in inverse susceptibility data at 200 K suggests a valence transition from Yb(2+) to Yb(3+) as the temperature decreases. An increase in doping of Cu at the Al2 position enhances the disorder in the system and enhancement in the trivalent nature of Yb. Electrical conductivity measurements show that all compounds are of a metallic nature.

Indium Flux-Growth of Eu2AuGe3: A New Germanide with an AlB2 Superstructure

The germanide Eu(2)AuGe(3) was obtained as large single crystals in high yield from a reaction of the elements in liquid indium. At room temperature Eu(2)AuGe(3) crystallizes with the Ca(2)AgSi(3) type, space group Fmmm, an ordered variant of the AlB(2) type: a = 857.7(4), b = 1485.5(10), c = 900.2(4) pm. The gold and germanium atoms build up slightly distorted graphite-like layers which consist of Ge(6) and Au(2)Ge(4) hexagons, leading to two different hexagonal-prismatic coordination environments for the europium atoms. Magnetic susceptibility data showed Curie-Weiss law behavior above 50 K and antiferromagnetic ordering at 11 K. The experimentally measured magnetic moment indicates divalent europium. The compound exhibits a distinct magnetic anisotropy based on single crystal measurements and at 5 K it shows a metamagnetic transition at ∼10 kOe. Electrical conductivity measurements show metallic behavior. The structural transition at 130 K observed in the single crystal data was very well supported by the conductivity measurements. (151)Eu Mössbauer spectroscopic data show an isomer shift of -11.24 mm/s at 77 K, supporting the divalent character of europium. In the magnetically ordered regime one observes superposition of two signals with hyperfine fields of 26.0 (89%) and 3.5 (11%) T, respectively, indicating differently ordered domains.

Ferromagnetic ordering in ThSi 2 type CeAu 0.28Ge 1.72

The compound CeAu 0.28Ge 1.72 crystallizes in the ThSi 2 structure type in the tetragonal space group I4 1/ amd with lattice parameters a= b=4.2415(6) Å c=14.640(3) Å. CeAu 0.28Ge 1.72 is a polar intermetallic compound having a three-dimensional Ge/Au polyanion sub-network filled with Ce atoms. The magnetic susceptibility data show Curie–Weiss law behavior above 50 K. The compound orders ferromagnetically at ∼8 K with estimated magnetic moment of 2.48 μ B/Ce. The ferromagnetic ordering is confirmed by the heat capacity data which show a rise at ∼8 K. The electronic specific heat coefficient ( γ) value obtained from the paramagnetic temperature range 15–25 K is∼124(5) mJ/ mol K 2. The entropy change due to the ferromagnetic transition is ∼4.2 J/mol K which is appreciably reduced compared to the value of R ln(2) expected for a crystal-field-split doublet ground state and/or Kondo exchange interactions.

Multifunctional hybrid materials based on transparent poly(methyl methacrylate) reinforced by lanthanoid hydroxo clusters

Three pentanuclear lanthanoid hydroxo clusters of composition [Ln(OH)(5)(abzm)(10)], where Ln = Eu, Tb, Ho and abzm = di(4-allyloxy)benzoylmethanide, have been prepared. The structures have been characterised by means of IR, Raman, elemental analyses and X-ray diffraction, showing a pyramidal square-based cluster core. The clusters (Tb and Ho) exhibit Curie-Weiss Law behaviour, displaying antiferromagnetic ordering at low temperatures. The emission properties of the Eu cluster demonstrate the abzm(-) ligand is an efficient antenna (λ(ex) = 420 nm) only for the sensitisation of Eu luminescence in the visible range, via energy transfer to the (5)D(0) state of the trivalent metal. The clusters have been reacted in the presence of methyl methacrylate and azobisisobutyronitrile to prepare reinforced polymers via radical polymerisation. The obtained materials exhibit swelling upon immersion into organic solvents up to ≈ 110% of their original size, in agreement with the presence of cluster-crosslinked polymeric chains. Also, no loss of transparency was observed in the preparation of the materials. The characteristic red emission of the Eu cluster in also retained in the polymeric material.

Mössbauer studies of Fe-doped HoMnO3

The crystallographic and magnetic properties of HoMn0.99Fe0.0157O3 powder have been studied by x-ray diffraction, superconducting quantum interference device measurements, and Mössbauer spectroscopy. It has a hexagonal space group P63cm with the lattice constants a0=6.139 and c0=11.402Å at room temperature. The magnetic susceptibility follows a Curie–Weiss law behavior, where the Curie–Weiss temperature was determined to be θCW=−18K. The Mössbauer spectra below TN=72K exhibit the six-line patterns, which coalesce into two lines above TN. The electric quadrupole splitting value at TN was ΔEQ=1.79±0.01mm∕s. An important point can be accessed that the direct observation of a coupling for the electric and magnetic order parameters was possible by Mössbauer spectroscopy.

Ferromagnetic ordering in bis(benzene)chromium(+) Bis(4,5-dimethoxybenzene-1,2-dithiolato)nickel(-).

The compound bis(benzene)chromium(+) bis(4,5-dimethoxy-1,2-benzenedithiolato)nickel(-), [Cr(bz)(2)](+)[Ni(dmox)(2)](-), was prepared as well-defined crystals by a metathesis reaction. X-ray single-crystal structure confirms the expected symmetries of the cations (D6h) and anions (D2h). The Ni-S bond length is typical for a monoanionic bis(arene)-1,2-dithiolato nickel complex thus confirming the ascribed charges. The structure reveals interpenetrating cation and anion sublattices where all ions are well separated from other ions of the same charge and with almost perpendicular symmetry planes of cations and anions. Above ca. 10 K the compound is paramagnetic and follows the Curie-Weiss law for S = 1/2 on each ion with a Weiss temperature of 8.5 K. Magnetic susceptibility and magnetization studies reveal the transition to a ferromagnetically ordered phase at 3.4 K. The ferromagnetic interaction is likely to occur through short contacts between anion heteroatoms (O and Ni) and cation H atoms, forming a 2-D network. A third dimension is possible through somewhat longer interionic S-H contacts. The Curie-Weiss law behavior can be modeled for 1-D chains with a ferromagnetic interaction of J = 11.6 K.

Environmental effect on the magnetic properties of Fe ions in glasses and ceramics

The effect of the environment on the magnetic properties of Fe-ions in a sodium germanate glass, a sodium silicate glass, and in the same devitrified glasses has been studied. In the four samples investigated, the inverse magnetic susceptibility ( χ −1) follows a Curie–Weiss law behavior with a negative Curie temperature θ p indicating an antiferromagnetic interaction in the four samples. The measurements also revealed that | θ p| in both glass matrices is relatively low (<10 K) while in the crystalline samples it increased by 4-fold in the silicate and by about 20-fold in the germanate. The molecular field coefficients γ m are negative for all four samples. The γ m values for the Fe-germanate glass and the crystalline sample are 3 and 10 times larger than the corresponding values for Fe-silicate. These results reflect a stronger exchange interaction in the germanate (glass and crystalline) than the silicate samples.

Superconductivity and magnetism in the system [Y 1−xCa x]SrBaCu 2.80(PO 4) 0.20O y with 0.10≤x≤0.40

We present the composite [Y 1−xCa x]SrBaCu 2.80(PO 4) 0.20O y (0.10≤x≤0.40) prepared at normal temperature and pressure conditions. X-ray diffraction patterns show that samples containing Ca crystallize in a 123 tetragonal structure with small amounts of impurities. The Rietveld method was used to refine the lattice constants. Ac and dc susceptibility measurements using a SQUID show that the materials are superconductors independent of Ca content. In the normal region the measurements of χ DC show a typical Curie-Weiss law behavior.

Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin

Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (2) dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mössbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10 11 s −1 for the pre-exponential frequency factor in the Néel–Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250–400 K. Sample 4 was indicated to be paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mössbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1–3 exhibited Curie–Weiss law behavior, indicating weak particle–particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin, possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.

Magnetic, Electrical Conductivity, and EPR Investigations of a Low-Spind5System in Fe8V10W16O85

The temperature dependence of the magnetic, electrical conductivity, and electron paramagnetic resonance (EPR) properties of Fe8V10W16O85has been investigated. The magnetic susceptibility measurements revealed an almost Curie–Weiss law behavior above room temperature and an additional magnetic interaction at low temperature, causing a steep rise of magnetization as the liquid helium temperature was approached. The value of the magnetic moment at high temperature,μeff=1.80μB, suggests a predominance of trivalent iron ions in a low-spin state. In the 300–4.2 K temperature range a difference between the zero field cooling (ZFC) and the field cooling (FC) modes was recorded. This irreversible behavior might be related to the presence of weakly coupled clusters. The EPR measurements revealed a broad, temperature-dependent resonance line at high temperature and two weaker lines at low temperature. The two low-temperature lines were attributed to antiferromagnetically coupled high-spin Fe3+ion clusters and to high-spin iron ions placed at sites with low symmetry of the crystal field. The broad line at high temperature was separated into two Lorentzian lines. These component lines were attributed to the two paramagnetic centers connected with the Fe3+ions involved in the magnetic structure of Fe8V10W16O85: dominant low-spin centers and a small admixture (<15%) of the high-spin centers. The line broadening and shift of the resonance field of the two component lines with decreasing temperature were studied and analyzed using a model of the EPR lines of antiferromagnets. The temperature dependence of the electrical conductivity showed a typical semiconducting-type behavior with an activation energy of 0.40 eV. The hopping mechanism of small polarons was proposed to explain the transport properties of the sample.

Synthesis, structural characterisation and magnetic properties of Gd14W4O33−xNy(0 ⩽ x ⩽ 17 ± 2, 0 ⩽ y ⩽ 9 ± 2), a new fluorite-related oxynitride

A series of crystalline Gd-W oxides, with Gd:W ratios spanning the values 0.1–3.5 has been prepared and treated with a flow of NH3(g) in the temperature range 700–1100°C. Besides the previously reported formation of GdWO3N and Gd2WO3N2, the following new results were obtained: (i) cubic Gd0.1 WO3 upon ammonolysis forms an (oxy)nitride Gd11.1 W(O, N)4 with an f.c.c. lattice: (ii) the previously described Gd2WO3N2 exhibits a solid solubility range Gd3−A W1−1(O,N)x with, approximately, (0 ⩽ x ⩽ 1: (iii) ammonolysis of Gd14W4O33 yields an oxynitride, the composition of which varies with the synthesis temperature according to Gd14W4Oin33−yNy(0 ⩽ x ⩽ 17 ± 2, 0 ⩽ y ⩽ 9 ± 2). All strong diffraction lines, including those of the pure oxide (x = y = 0), can be indexed with a body-centred monoclinic unit cell derived from that of fluorite. For Gd14W4O33 the cell parameters are a = 5.3592(11), b = 3.7295(7), c = 3.8636(8) Å, β = 92.170(2)° and V = 77.17 Å3. However, strong superstructures reflections in the electron diffraction patterns indicate that the true unit cell is considerably larger. A partial structure determination of Gd14W4O33−xNx has been carried out by the Rietveld method. Magnetic susceptibility measurements in the temperature interval 15–300 K show a Curie-Weiss law behaviour for Gd14W4O33−xNxN with μeff = 8.08 ± 0.06 Bohr magnetons per Gd3+ and θ = − 12.4 ± 1.1 K for all compositions.

High-valent manganese in polyoxotungstates—II. Oxidation of the tetramanganese heteropolyanion [Mn 4(H 2O) 2(PW 9O 34) 2] 10−

Oxidation of the heteropolyanion [Mn 4 II(H 2O) 2(PW 9O 34) 2] 10− ( 0) with potassium persulphate yielded mixed valence Mn II,III products reproducibly isolated as the green potassium salt of [Mn 4(H 2O) 2(PW 9O 34) 2] 9− ( 1) and the brown potassium-caesium salt of [Mn 4(OH) 2(PW 9O 34) 2] 9− ( 2). Coulometric and single crystal X-ray structure analysis revealed that 1 and 2 are one- and three-electron oxidized derivatives of 0 and are isostructural with 0. Slight metrical variations among 0, 1 and 2 appear in some MnO bond distances, which suggest that oxidation has occurred first at the aquated Mn(2) centres of 0. The magnetic susceptibility of 1 between 2 and 300 K shows Curie-Weiss law behaviour, θ = −27.35 K, without the maximum for χ at T ≈ 16 K previously observed for 0.

Preparation structure and physical properties of new silver lanthanide molybdenum oxides [AgLnMo 2O 8 (Ln = La-Nd and Sm)

We present the synthesis of AgLnMo 2O 8 compounds with Ln = La-Nd and Sm. These compounds represent a scheelite-type structure characterized by MoO 4-tetrahedrons. IR spectra show five absorption peaks in the region of 1000-400cm −1, around 800cm −1 and 400cm −1, which correspond to the modes of the tetrahedral MoO 2− 4 groups. All of AgLnMo 2O 8 (Ln = La-Nd and Sm) oxides are dielectric materials at room temperature. The temperature dependence of the magnetic susceptibility of AgLnMo 2O 8 (Ln = Ce-Nd and Sm) shows Curie-Weiss law behavior from 100K to 300K. This indicates that both Ce and Pr exist in +3 oxidation state in AgLnMo 2O 8. For AgLaMo 2O 8, diamagnetic properties are found as expected.

Semiconductor to metal transition in Ln 2Mo 3O 9 compounds

Ln 2Mo 3O 12 and Ce 2Mo 3O 12.25 are reduced by hydrogen yielding Mo 4+ oxides of the formula Ln 2Mo 3O 9 (Ln = La, Ce, Pr, Nd, Sm, Gd and Dy). The new compound Ce 2Mo 3O 9 has the same structure as other Ln 2Mo 3O 9 compounds. All of the products are single phase materials and crystallize in a tetragonal scheelite type structure with Mo 2O 6 clusters. The IR spectra of the Ln 2Mo 3O 9 oxides show two absorption bands. These compounds are black n-type semiconductors and exhibit Curie-Weiss Law behavior from 100K to 250K. Temperature dependence of the electrical properties of these compounds were measured for the first time, and a semiconductor-metal transition was found at about 250 °C.