Curie-Weiss Paramagnetism Research Articles

Study of negative thermal expansion in the frustrated spinel ZnCr2Se4

The origin of negative thermal expansion (NTE) in the bond frustrated ZnCr2Se4 has been explored. ESR and FTIR document an ideal paramagnetic state above 100 K, below which ferromagnetic clusters coexist with the paramagnetic state down to TN. By fitting the inverse susceptibility above 100 K using a modified paramagnetic Curie-Weiss law, an exponentially changeable exchange integral J is deduced. In the case of the variable J, magnetic exchange and lattice elastic energy couple with each other effectively via magnetoelastic interaction in the ferromagnetic clusters, where NTE occurs at a loss of exchange energy while a gain of lattice elastic one.

Intermetallic magnesium compounds RE 2RuMg3 (RE = Dy, Ho, Er, Tm, Lu) and RE 3Ru2Mg (RE = Sc, Er, Lu) with bcc Superstructures

Abstract The intermetallic magnesium compounds RE 2RuMg3 (RE = Dy, Ho, Er, Tm, Lu) and RE 3Ru2Mg (RE = Sc, Er, Lu) were synthesized from the elements in sealed niobium tubes in muffle or induction furnaces using different annealing sequences. The polycrystalline RE 2RuMg3 and RE 3Ru2Mg samples were characterized through Guinier powder patterns. The structures of Er2RuMg3 and Sc3Ru2Mg were refined on the basis of single-crystal X-ray diffractometer data: new type, P4/mmm, a = 336.71(9), c = 1234.6(7) pm, wR = 0.0327, 240 F val­ues, 12 variables for Er2RuMg3 and a = 324.67(6), c = 1077.2(3) pm, wR = 0.0345, 273 F values, 12 variables for Sc3Ru2Mg. The Er2RuMg3 and Sc3Ru2Mg structures are i3 superstructures of the CuAu type and thus belong to the large family of ordered bcc derivatives. The fundamental building units are distorted ErRu, ScRu, ScMg, and ErMg cubes. The magnesium-rich phase Er2RuMg3 has a pronounced Mg substructure (314–337 pm Mg–Mg) with distorted cuboctahedral coordination. This sub­structure is compared to other magnesium-rich compounds. Temperature dependent magnetic susceptibility studies show Curie-Weiss paramagnetism for RE 2RuMg3 (RE = Dy, Ho, Er, Tm) with experimental magnetic moments close to the RE 3+ free ion values. The compounds exhibit antiferromagnetic ordering at Néel temperatures of 6.5(1), 3.6(5), 3.5(5), and 5(1) K, respectively. Metamagnetic transitions underline the stable antiferromagnetic ground states. Lu2RuMg3 is a Pauli paramagnet.

Structural, magnetic and electronic transport studies of RAgSn2 compounds (R = Y, Tb, Dy, Ho and Er) with Cu3Au-type

RAgSn2 compounds, where R = Y, Tb, Dy, Ho and Er, were synthesized by arc-melting and subsequent annealing at 870 K. The formation of cubic phases with Cu3Au-type structure (space group \({\textit{Pm}}{\overline{3}}{\textit{m}}\)) was studied. Magnetic property measurements showed that in paramagnetic state, the compounds with magnetic rare-earth atoms are Curie–Weiss paramagnets and order antiferromagnetically at low temperatures. YAgSn2 is a Pauli paramagnet in 100–300 K temperature range. The electrical properties of RAgSn2 compounds were investigated by means of electrical resistivity and Seebeck coefficient measurements in 4·2–300 K temperature range. All investigated compounds exhibit metallic type of conductivity. Electronic structure calculations based on full potential linearized augmented plane wave (FLAPW) method is also carried out to probe the magnetic and electronic structures of RAgSn2 compounds. Comparisons between experimental data and calculations are discussed.

New tetragonal derivatives of cubic NaZn13-type structure: RNi6Si6 compounds, crystal structure and magnetic ordering (R=Y, La, Ce, Sm, Gd–Yb)

Novel RNi6Si6 compounds adopt the new CeNi6Si6-type structure for R=La–Ce (tP52, space group P4/nbm N 125-1) and new YNi6Si6-type structure for R=Y, Sm, Gd–Yb (tP52, space group P4¯b2N 117) that are tetragonal derivative of NaZn13-type structure, like LaCo9Si4-type.The CeNi6Si6, GdNi6Si6, TbNi6Si6, DyNi6Si6 and HoNi6Si6 compounds are Curie–Weiss paramagnets down to ~30K, and do not order magnetically down to 5K. However, the inverse paramagnetic susceptibility of LaNi6Si6 does not follow Curie–Weiss law.The DyNi6Si6 shows ferromagnetic-like saturation behaviour at 5K in applied fields of 50kOe, giving rise to a magnetic moment value of 6.5μB/f.u. in 50kOe. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi6Si6 with K=[±1/4, ±1/4, 0] wave vector below ~10K.

Magnetism and magnetocaloric effect in multicomponent Laves-phase compounds: Study and comparative analysis

This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R0.9R′0.1)1−xGdxCo2 solid solutions with R=Dy, Ho and R′=Er, Ho and x varied from 0.05 to 0.15. Powder X-ray diffraction analysis performed at room temperature revealed that all studied solid solutions solidify with the formation of a Laves-phase MgCu2-type structure (space group Fd−3m). The magnetization behavior and the magnetic transition are analyzed in terms of the Landau theory. The studies of magnetic properties and heat capacity showed that a relatively small Gd addition significantly increases TC of the compounds. The maximum percentage increase in TC, namely, ~43% was observed for (Ho0.9Er0.1)1−xGdxCo2. However, the highest temperature was noted for the (Dy0.9Ho0.1)0.85Gd0.15Co2 solid solution; it is TC=183.4K. Below the ordering temperature, all samples are ferrimagnetically ordered; at high temperatures, they are Curie–Weiss paramagnets. Moreover, a small Gd addition eliminates the field-induced magnetic transition near TC and, as consequence, transforms the nature of magnetic transition from the first- to second-order.The magnetocaloric effect has been estimated in terms of both isothermal magnetic entropy and adiabatic temperature changes. The highest adiabatic temperature change ΔTad=3K and highest isothermal entropy change ΔSmag=12.1J/kgK were observed for (Ho0.9Er0.1)0.95Gd0.05Co2 at ~90K in magnetic fields of 2T and 3T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of ΔSmag were observed for the (Dy0.9Ho0.1)1−xGdxCo2 solid solutions. Under an external field change of from 0 to 3T, the maximum entropy change for (Dy0.9Ho0.1)1−xGdxCo2 compounds decreases from 6.9at x=0.05–4.3J/kgK at x=0.15. The refrigerant capacity for all solid solutions (with 0.05≤x≤0.15) is reported. The effect of increasing Gd content in the solid solutions on their magnetic and magnetocaloric properties is discussed.

New Rhodium‐rich Germanides RERh6Ge4 (RE = Y, La, Pr, Nd, Sm–Lu)

Abstract The ternary germanides RERh6Ge4 (RE = Y, La, Pr, Nd, Sm–Lu) were obtained by arc‐melting of the elements and subsequent annealing. Single crystals were grown from bismuth fluxes. The samples were studied by X‐ray diffraction on powders. The structures of five members were refined from single crystal diffraction data: LiCo6P4 type, P$\bar{6}$m2, a = 715.8(1), c = 387.33(8) pm, wR = 0.0238, 332 F2 values for LaRh6Ge4, a = 715.0(1), c = 384.96(7) pm, wR = 0.0211, 329 F2 values for PrRh6Ge4, a = 714.28(9), c = 382.57(6) pm, wR = 0.0136, 327 F2 values for SmRh6Ge4, a = 714.2(1), c = 381.6(1), wR = 0.0270, 327 F2 values for GdRh6Ge4, and a = 714.2(2), c = 379.0(1) pm, wR = 0.0273, 324 F2 values for HoRh6Ge4 with 19 variables per refinement. The RERh6Ge4 structures have two crystallographically independent germanium sites in trigonal prismatic coordination, manifesting the close structural relationship with metal‐rich phosphides. Together, the rhodium and germanium atoms build up three‐dimensional [Rh6Ge4] networks, which leave large channels for the rare earth atoms. Each rare earth atom has coordination number 20 with 12 Rh, 6 Ge, and 2 RE neighbors. Temperature dependent magnetic susceptibility measurements indicate Pauli paramagnetic behavior for YRh6Ge4, LaRh6Ge4, and LuRh6Ge4. The compounds RERh6Ge4 (RE = Gd–Yb) are Curie‐Weiss paramagnets. Antiferromagnetic ordering was observed at 8.4(5) K (GdRh6Ge4), 13.6(5) K (TbRh6Ge4), 5.1(5) K (DyRh6Ge4), and 8.9(5) K (YbRh6Ge4). DyRh6Ge4 and YbRh6Ge4 show metamagnetic transitions at 2.5(5) and 45(2) kOe, respectively.

Ternary Antimonides RE4T7Sb6 (RE=Gd–Lu; T =Ru, Rh) with Cubic U4Re7Si6-type Structure

The ternary antimonides RE4T7Sb6 (RE=Gd-Lu; T =Ru, Rh) have been synthesized from the elements by arc-melting and subsequent annealing in an induction furnace. The samples have been characterized by powder X-ray diffraction. Four structures were refined on the basis of single-crystal X-ray diffractometer data: U4Re7Si6 type, space group Im3m with a=862.9(2) pm, wR2=0.0296, 163 F2 values for Er4Ru7Sb6; a=864.1(1) pm, wR2=0.1423, 153 F2 values for Yb4Ru7Sb6; a=872.0(2) pm, wR2=0.0427, 172 F2 values for Tb4Rh7Sb6; and a=868.0(2) pm, wR2=0.0529, 154 F2 values for Er4Rh7Sb6, with 10 variables per refinement. The structures have T1@Sb6 octahedra and slightly distorted RE@T26Sb6 cuboctahedra as building units. The distorted cuboctahedra are condensed via all trapezoidal faces, and this network leaves octahedral voids for the T1 atoms. The ruthenium-based series of compounds was studied by temperature-dependent magnetic susceptibility measurements. Lu4Ru7Sb6 is Pauli-paramagnetic. The antimonides RE4Ru7Sb6 with RE=Dy, Ho, Er, and Tm show Curie-Weiss paramagnetism. Antiferromagnetic ordering occurs at 10.0(5), 5.1(5) and 4.0(5) K for Dy4Ru7Sb6, Ho4Ru7Sb6 and Er4Ru7Sb6, respectively, while Tm4Ru7Sb6 remains paramagnetic. Yb4Ru7Sb6 is an intermediate-valent compound with a reduced magnetic moment of 3.71(1) μB per Yb as compared to 4.54 μB for a free Yb3+ ion

Co(NCS)2(1,2-bis(2-pyridyl)ethylene)]n: A new 1D coordination polymer that shows a metamagnetic transition

Reaction of Co(NCS)2 with 1,2-bis(2-pyridyl)ethylene (2-bpe) leads to four new coordination compounds of composition [Co(NCS)2(CH3OH)4]·2(2-bpe) solvate (1), Co(NCS)2(2-bpe)2(CH3OH)2 (2), Co(NCS)2(2-bpe)2 (3) and Co(NCS)2(2-bpe) (4). The crystal structure of compounds 1 and 2 consists of discrete complexes in which the cobalt(II) cations are octahedral coordinated by two terminal thiocyanato anions and four methanol molecules in 1 and by two terminal N-bonded thiocyanato anions, two 2-bpe ligands and two methanol molecules in 2. In compound 3 also discrete complexes are found but in contrast to 1 and 2 each cobalt(II) cation is tetrahedral coordinated by two terminal N-bonded thiocyanato anions and two 1,2-bis(2-pyridyl)ethylene (2-bpe) ligands. In the most 2-bpe deficient compound 4 the Co cations are also tetrahedral coordinated but the metal cations are linked into chains by the 2-bpe ligands. Magnetic measurements on compound 3 shows only Curie–Weiss paramagnetism whereas for compound 4 a metamagnetic transition is observed at a critical field of HC=1.9kOe with antiferromagnetic ordering below and saturated paramagnetism above HC. These results are compared with those for the corresponding compound with 1,2-bis(4-pyridyl)ethylene as ligand.

Experimental study of the magnetocaloric effect in Dy1−xErxCo2 solid solutions doped with Gd

Magnetic and magnetocaloric properties of polycrystalline (Dy0.9Er0.1)1−xGdxCo2 (0.0 ⩽ x ⩽ 0.25) solid solutions were investigated experimentally using magnetic measurements. The magnetization behavior and magnetic transition are analyzed in terms of Landau theory. Powder X-ray diffraction analysis performed at room temperature showed that all (Dy0.9Er0.1)1−xGdxCo2 (0.0 ⩽ x ⩽ 0.25) solid solutions are C15 cubic Laves phase with the MgCu2-type structure. The lattice parameter increases from 0.7187 for Dy0.9Er0.1Co2 to 0.7204 nm for (Dy0.9Er0.1)0.75Gd0.25Co2. In this case, the Curie temperature increases from 128 K to 215 K for. At higher temperatures, all solid solutions are Curie–Weiss paramagnets. The isothermal entropy change −ΔSmag was calculated using magnetic measurements data and thermodynamic Maxwell’s relation. A decrease in the entropy change has been observed with increasing Gd content. Under an external field change of from 0 to 3 T, the maximum entropy change for these compounds decreases from 8.5 at x = 0.0 to 3.1 J/kg K at x = 0.25. The refrigerant capacity of the (Dy0.9Er0.1)1−xGdxCo2 solid solutions (with 0.0 ⩽ x ⩽ 0.25) is presented. The effect of increasing Gd content in the (Dy0.9Er0.1)1−xGdxCo2 solid solutions on their magnetic and magnetocaloric properties is discussed.

Synthesis, structures and magnetic properties of new Fe(II) and Co(II) thiocyanato coordination compounds with 2-chloropyrazine as Co-ligand

Investigations on the synthesis of coordination compounds based on Fe(NCS)2 and Co(NCS)2 with 2-chloropyrazine as ligand leads to the formation of five new compounds. Fe(NCS)2(2-chloropyrazine)4 (1-Fe), Co(NCS)2(2-chloropyrazine)4 (1-Co) and Fe(NCS)2(2-chloropyrazine)4·2-chloropyrazine solvate (2-Fe) consists of discrete complexes in which the metal cations are octahedrally coordinated and in which the thiocyanato anions are only terminal coordinated. On heating 1-Fe and 1-Co transform into new coordination polymers of composition [Fe(NCS)2(2-chloropyrazine)2]n (3-Fe) and [Co(NCS)2(2-chloropyrazine)2]n (3-Co) which are isotypic. No access to large and phase pure amounts of these compounds was found in solution but the structure of 3-Co was determined from a crystal obtained in one batch by accident. In the crystal structure of 3-Co and 3-Fe the metal(II) cations are coordinated by two N-bonded as well as two S-bonded thiocyanato anions and two 2-chloropyrazine ligands and are linked by μ-1,3-bridging anions into layers. Magnetic measurements of 1-Fe and 1-Co show only Curie- or Curie–Weiss paramagnetism, whereas for 3-Fe antiferromagnetic ordering and for 3-Co metamagnetic behavior is observed.

Magnetic, transport and electronic properties of CeAu1−xNixIn intermetallics

Polycrystalline compounds CeAu1−xNixIn (x=0.2, 0.4, 0.6 and 0.8) and their La-based counterparts were investigated by means of X-ray diffraction, magnetic, electrical resistivity and X-ray photoelectron spectroscopy (XPS) measurements. All these materials crystallize in the hexagonal ZrNiAl-type structure. The CeAu1−xNixIn alloys with x⩽0.6 exhibit Curie–Weiss paramagnetism down to the lowest temperatures studied, while that with x=0.8 shows a magnetic behavior characteristic of intermediate valence systems. In all the alloys, the electrical transport is influenced by Kondo effect, which for x⩽0.4 transforms with decreasing temperature from incoherent to coherent scattering, while for larger x exhibits single-ion character in the entire temperature range investigated. The XPS data indicates sizable hybridization of the Ce-4f electrons with conduction band, with the average occupation factor of the 4f1 ground state systematically diminishing with increasing the Ni content.

Structures and Magnetic Properties of Nickel Thiocyanato Coordination Compounds with 2‐Chloropyrazine as a Neutral Coligand

AbstractReaction of Ni(NCS)2 with 2‐chloropyrazine in different molar ratios and solvents at room temperature leads to five new coordination polymers. In the crystal structures of Ni(NCS)2(2‐chloropyrazine)4·2‐chloropyrazine solvate (1) and Ni(NCS)2(2‐chloropyrazine)4 (2) the nickel cations are octahedrally coordinated by two terminal N‐bonded thiocyanato anions and four 2‐chloropyrazine ligands into discrete complexes. In the crystal structures of the Ni(NCS)2(2‐chloropyrazine)2(CH3OH)2·(CH3OH)2 solvate (3) and Ni(NCS)2(2‐chloropyrazine)2(CH3OH)2 (4) each nickel(II) cation is coordinated by two terminal N‐bonded thiocyanato anions, two 2‐chloropyrazine ligands and two O‐bonded methanol molecules in a slightly distorted octahedron. On heating, compounds 1 and 2 transform into the ligand‐deficient 1:2 compound 5, which can also be crystallized from solution. In the crystal structure of [Ni(NCS)2(2‐chloropyrazine)2]n (5) each nickel(II) cation is coordinated by two N‐bonded and two S‐bonded thiocyanato anions as well as two 2‐chloropyrazine ligands. The nickel cations are linked into dimers by pairs of μ‐1,3‐bridging thiocyanato anions that are further linked into chains and finally into layers by single μ‐1,3‐bridging thiocyanato anions. Magnetic measurements of compound 1 and 2 show only Curie or Curie–Weiss paramagnetism, whereas in the ligand‐deficient compound 5 a metamagnetic transition is observed at a critical field of HC = 14 kOe. The results of the magnetic measurements are compared with those of related nickel compounds with different coligands.

Bisdithiazolyl Radical Spin Ladders

A series of four bisdithiazolyl radicals 1a-d (R(1) = Pr, Bu, Pn, Hx; R(2) = F) has been prepared and characterized by X-ray crystallography. The crystal structure of 1a (R(1) = Pr) belongs to the tetragonal space group P42(1)m and consists of slipped π-stack arrays of undimerized radicals packed about 4 centers running along the z-direction, an arrangement identical to that found for 1 (R(1) = Et; R(2) = F). With increasing chain length of the R(1) substituent, an isomorphous set 1b-d is generated. All three compounds crystallize in the P2(1)/c space group and consist of pairs of radical π-stacks locked together by strong intermolecular F···S' bridges to create spin ladder arrays. The slipped π-stack alignment of radicals produces close S···S' interactions which serve as the "rungs" of a spin ladder, and the long chain alkyl substituents (R(1)) serve as buffers which separate the ladders from each other laterally. Variable temperature magnetic susceptibility measurements indicate that 1a behaves as an antiferromagnetically coupled Curie-Weiss paramagnet, the behavior of which may be modeled as a weakly coupled AFM chain. Stronger antiferromagnetic coupling is observed in 1b-d, such that the Curie-Weiss fit is no longer applicable. Analysis of the full data range (T = 2-300 K) is consistent with the Johnston strong-leg spin ladder model. The origin of the magnetic behavior across the series has been explored with broken-symmetry Density Functional Theory (DFT) calculations of individual pairwise exchange energies. These confirm that strong antiferromagnetic interactions are present within the ladder "legs" and "rungs", with only very weak magnetic exchange between the ladders.

Phosphide Oxides RE2AuP2O (RE = La, Ce, Pr, Nd): Synthesis, Structure, Chemical Bonding, Magnetism, and 31P and 139La Solid State NMR

Polycrystalline samples of the phosphide oxides RE(2)AuP(2)O (RE = La, Ce, Pr, Nd) were obtained from mixtures of the rare earth elements, binary rare earth oxides, gold powder, and red phosphorus in sealed silica tubes. Small single crystals were grown in NaCl/KCl fluxes. The samples were studied by powder X-ray diffraction, and the structures were refined from single crystal diffractometer data: La(2)AuP(2)O type, space group C2/m, a = 1515.2(4), b = 424.63(8), c = 999.2(2) pm, β = 130.90(2)°, wR2 = 0.0410, 1050 F(2) values for Ce(2)AuP(2)O, and a = 1503.6(4), b = 422.77(8), c = 993.0(2) pm, β = 130.88(2)°, wR2 = 0.0401, 1037 F(2) values for Pr(2)AuP(2)O, and a = 1501.87(5), b = 420.85(5), c = 990.3(3) pm, β = 131.12(1)°, wR2 = 0.0944, 1143 F(2) values for Nd(2)AuP(2)O with 38 variables per refinement. The structures are composed of [RE(2)O](4+) polycationic chains of cis-edge-sharing ORE(4/2) tetrahedra and polyanionic strands [AuP(2)](4-), which contain gold in almost trigonal-planar phosphorus coordination by P(3-) and P(2)(4-) entities. The isolated phosphorus atoms and the P(2) pairs in La(2)AuP(2)O could clearly be distinguished by (31)P solid state NMR spectroscopy and assigned on the basis of a double quantum NMR technique. Also, the two crystallographically inequivalent La sites could be distinguished by static (139)La NMR in conjunction with theoretical electric field gradient calculations. Temperature-dependent magnetic susceptibility measurements show diamagnetic behavior for La(2)AuP(2)O. Ce(2)AuP(2)O and Pr(2)AuP(2)O are Curie-Weiss paramagnets with experimental magnetic moments of 2.35 and 3.48 μ(B) per rare earth atom, respectively. Their solid state (31)P MAS NMR spectra are strongly influenced by paramagnetic interactions. Ce(2)AuP(2)O orders antiferromagnetically at 13.1(5) K and shows a metamagnetic transition at 11.5 kOe. Pr(2)AuP(2)O orders ferromagnetically at 7.0 K.

Ce2PdIn8, Ce3PdIn11 and Ce5Pd2In19—members of homological series based on AuCu3- and PtHg2-type structural units

Crystal structures of three members of a unique homological series with the general formula CemPdnIn3m+2n based on the AuCu3 and PtHg2 structure types were studied by single-crystal X-ray diffraction. The compounds crystallize with space group P4/mmm (Z=1) and the lattice parameters: a=4.6900(9)Å, c=12.185(6)Å for Ce2PdIn8, a=4.6846(8)Å, c=16.846(8)Å for Ce3PdIn11, and a=4.70120(10)Å, c=29.1359(4)Å for Ce5Pd2In19. The crystal structures of Ce3PdIn11 and Ce5Pd2In19 represent new types. The three structures constitute of [CeIn3] cuboctahedra layers and [PdIn2] rectangular polyhedra layers, alternating along the tetragonal c-axis in accordance with the m:n proportion. The magnetic and electrical transport properties of the novel compounds Ce3PdIn11 and Ce5Pd2In19 were investigated down to 1.72K. Both indides are Curie–Weiss paramagnets due to the presence of fairly well localized 4f electrons of trivalent cerium ions. The electrical resistivity of both materials is dominated over an extended temperature range by strong spin–flip Kondo interactions with the characteristic temperature scale of 20–30K.

Exploration and synthesis of condensed coordination networks with modified magnetic properties

Eight new coordination polymers based on Ni(NCS)2 and 2-methylpyrazine were discovered, structurally characterized and most of them investigated for their thermal and magnetic properties. In the crystal structures of Ni(NCS)2(2-methylpyrazine)4 (1), Ni(NCS)2(2-methylpyrazine)4·2-methylpyrazine solvate (2) and Ni(NCS)2(2-methylpyrazine)4·ethanol solvate (3), the nickel(II) cations are always octahedral coordinated by two terminal N-bonded thiocyanato anions and four N-bonded 2-methylpyrazine ligands into discrete complexes. The crystal structures of Ni(NCS)2(2-methylpyrazine)2(H2O)2 (4) and Ni(NCS)2(2-methylpyrazine)2(CH3OH)2 (5) also consist of discrete complexes, but in contrast to compounds 1–3 two terminal bonded 2-methylpyrazine ligands are exchanged by two water and methanol molecules, respectively. In [Ni(NCS)2(2-methylpyrazine)3(H2O)]·[Ni(NCS)2(2-methylpyrazine)4] (6) two different complexes are observed, in which one nickel(II) cation is coordinated by two terminal N-bonded thiocyanato anions, three 2-methylpyrazine ligands and one water molecule, whereas the second cation is coordinated by two terminal N-bonded thiocyanato anions and four 2-methylpyrazine ligands. Compounds 2, 3, 4 and 5 transformed into a 2-methylpyrazine deficient 1 : 2 (1 : 2 = ratio between metal and 2-methylpyrazine) compound with the composition Ni(NCS)2(2-methylpyrazine)2 (7) on heating. On further heating this compound subsequently transformed into a 1 : 1 compound with the composition [Ni(NCS)2(2-methylpyrazine)]n (8). Compound 7 can only be prepared by thermal decomposition and therefore, its structure was solved ab initio from X-ray powder data. It consists of [Ni(NCS)]2 dimers that are μ-1,3-bridged by single thiocyanato anions into layers. Single crystal structure analysis of compound 8 proves that nickel(II) cations are linked by the thiocyanato anions into Ni–(NCS)2–Ni double chains, which are further connected by the 2-methylpyrazine ligands into layers. Magnetic measurements on compounds 2, 3, 4 and 5 show only Curie or Curie–Weiss paramagnetism, whereas in the ligand-deficient compound 7 metamagnetic behavior is observed. The results of these investigations are discussed and compared with those obtained for related coordination compounds with e.g. pyrazine and pyridine as neutral co-ligands.

Synthesis, structures and magnetic properties of Fe(ii) and Co(ii) thiocyanato coordination compounds: on the importance of the diamagnetic counterparts for structure determination

Reaction of Fe(NCS)2 and Co(NCS)2 with 2-methylpyrazine in different molar ratios and solvents at room temperature leads to the formation of five new coordination compounds of composition M(NCS)2(2-methylpyrazine)2(H2O)2 (M = Fe (1-Fe) , Co (1-Co)), Co(NCS)2(2-methylpyrazine)2(CH3OH)2 (2-Co) and Co(NCS)2(2-methylpyrazine)4·2-methylpyrazine solvate (3-Co). In all of these compounds, discrete complexes are found in which the metal cations are octahedrally coordinated by two terminal N-bonded thiocyanato anions and four N- or O-donor co-ligands. On heating compounds 1-3 in a thermobalance new coordination polymers of composition M(NCS)2(2-methylpyrazine)2 (M = Co (4-Co) , Fe (4-Fe)) are obtained in the first step, which transform into M(NCS)2(2-methylpyrazine) (M = Co (5-Co) , Fe (5-Fe)) in the second. Because of the low chalcophilicity of these cations, compounds 4 and 5 are not accessible from solution. Further investigations prove that 4-Co and 4-Fe obtained by thermal decomposition are of low crystallinity, might be isotypic and might consist of metal cations, in which the anionic ligands are only terminal N-bonded. In contrast, 5-Co and 5-Fe are of good crystallinity but their structure cannot be solved from X-ray powder data. However, a compound of the same composition (5-Cd) based on the more chalcophilic cadmium can easily be crystallized from solution and characterized by single crystal X-ray diffraction. This compound is isotypic to 5-Co and 5-Fe and therefore their structures were determined by Rietveld refinements. In their crystal structures the metal atoms are linked by μ-1,3-bridging thiocyanato anions into a 2D network. Magnetic measurements reveal that compounds 1-4 show only Curie-Weiss paramagnetism and that for 5-Fe antiferromagnetic ordering is observed. In contrast, 5-Co shows metamagnetic behavior with a very large critical field. Finally, it was shown that 4-Co and 4-Fe are hygroscopic and transform within minutes into the hydrates 1-Co and 1-Fe.

Insight into lithium transport in lithium nitridometallate battery materials from muon spin relaxation

Muon spin relaxation and powder neutron diffraction have been combined to study three lithium cobalt nitride battery materials. Neutron diffraction shows that these retain the P6/mmm space group of Li(3)N with Co located only on Li(1) sites. The lattice parameters vary smoothly with the degree of metal substitution, such that the [Li(2)N] layers expand while the layer separation contracts, as observed previously for similar series of Cu- and Ni-substituted materials. However, in contrast to the latter, the Li(3-x-y)Co(x)N phases exhibit Curie-Weiss paramagnetism and this prevents the use of nuclear magnetic resonance to measure Li(+) transport parameters. Therefore, muon spin relaxation has been employed here as an alternative technique to obtain quantitative information about Li(+) diffusion. Muon spin relaxation shows that Li(+) diffusion in Li(3-x-y)Co(x)N is anisotropic with transport confined to the [Li(2)N] plane at low temperature and exchange between Li(1) and Li(2) sites dominant at high temperature. By a comparison with previous studies some general trends have been established across a range of Cu-, Ni- and Co-substituted materials. For intra-layer diffusion E(a) decreases as metal substitution increases and the corresponding expansion of the layers results in a more open pathway for Li(+) diffusion. However, an optimal value of x is found with a ≈ 3.69 Å after which the concomitant contraction in layer spacing reduces the polarizability of the lattice framework.

Hydrogenation studies on structural and magnetic properties of antiferromagnetic Kondo lattice Ce2Cu2In

Hydrogenation studies were carried out on an antiferromagnetic dense Kondo system Ce2Cu2In. Single-phase hydrides Ce2Cu2InHx were obtained for the hydrogen content 2.17<x<2.8. These compounds form with the crystal lattice of the parent alloy, yet with a strongly expanded unit cell, especially along the crystallographic c-axis. For x<2.17 mixtures of Ce2Cu2In and Ce2Cu2InH∼2.2 were observed, while for x>3 amorphous material was obtained. The single-phase hydrides Ce2Cu2InH2.37 and Ce2Cu2InH2.78 are Curie–Weiss paramagnets due to stable Ce3+ ions. For both compounds, near 11–13K, some tiny features were observed in the magnetic susceptibility data, which might reflect weak magnetic ordering.

Crystal structure and physical properties of the new intermetallics REPt4In4 (RE = Gd – Lu, Y)

A new compound ErPt4In4 was synthesized by arc melting and its crystal structure was determined from the single crystal X-ray diffraction data: space group P63/mmc, a = 4.5321(9) Å, c = 19.807(13) Å, Pearson symbol hP18. The new structure type is composed of condensed via side edges Er-centered polyhedra [Pt8In6] and the corrugated slabs of In atoms alternating in the c-direction. A few isostructural compounds were found to form with Gd–Lu, and Y. The low-temperature physical properties of TbPt4In4, DyPt4In4 and YbPt4In4 were characterized by means of magnetic susceptibility and electrical resistivity measurements. All three compounds exhibit Curie–Weiss paramagnetism, due to the presence of well localized magnetic moments carried on trivalent rare-earth atoms, and metallic character of their electrical conductivity. The compounds TbPt4In4 and DyPt4In4 order magnetically below 8 and 5 K, respectively, whereas YbPt4In4 remains paramagnetic down to 1.7 K.