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We prepared an organically templated magnet, (enH2)0.5VPO4OH (enH2 = diprotonated ethylenediamine), hydrothermally and characterized its crystal structure by powder X-ray diffraction and Fourier-transform infrared spectroscopy, and its physical properties by magnetization, specific heat and nuclear magnetic resonance measurements and density functional theory calculations. (enH2)0.5VPO4OH consists of uniform chains of V3+ (d2, S = 1) ions and exhibits Haldane magnetism with spin gap Δ = 59.3 K from the magnetic susceptibility χ(T) at μ0H = 0.1 T, which is reduced to 48.4 K at μ0H = 9 T according to the 31P shift. The NMR data evidence the formation of a spin-glass state of unpaired S = 1/2 spins at TS–G ≈ 3 K and indicate that the Haldane S = 1 spin chain segments are much longer in the organically templated magnet (enH2)0.5VPO4OH than in the ammonium counterpart NH4VPO4OH. The single-ion anisotropy D and the interchain exchange J′ in (enH2)0.5VPO4OH and NH4VPO4OH were estimated in density functional calculations to find them very weak compared to the intrachain exchange J. [ABSTRACT FROM AUTHOR]

Potassium manganese fluoride phosphate, KMnPO4F, has been obtained through mild hydrothermal synthesis and characterized by scanning electron microscopy, microprobe analysis and X-ray diffraction. The compound possesses an orthorhombic symmetry and chiral space group P212121 with a = 4.7884(2), b = 9.0172(4), c = 9.5801(4) Å, and Z = 4. Its crystal structure is composed of Mn3+O4F square pyramids sharing vertices with PO4 tetrahedra. This anionic framework is neutralized by K+ cations. As the temperature decreases, a short-range correlation state (Tmax ∼ 35 K) of KMnPO4F is formed, followed by the establishment of antiferromagnetic (AFM) long-range order at TN = 25 K. The latter is marked by sharp λ-type anomalies in both Fisher's specific heat d(χkT)/dT and heat capacity Cp. Pulsedmagnetic field measurements on the single crystals identify the a axis as the easy magnetic axis and reveal a spin-flop transition at μ0Hspin-flop = 19 T. Density functional theory indicates that in variance with the three-dimensional network of KMnPO4F, it is a two-dimensional Ising magnetic system represented by buckled layers of integer spins S = 2 of Mn3+ ions. The strongest AFM exchange interaction, J1 ∼ -13 K, couples Mn3+ ions into linear chains running along the a axis. The chains themselves are ferromagnetically connected (J3 ∼ -4 K) within the ab plane. The interplane AFM exchange interaction (J2 ∼ -1 K) is weak and frustrated. [ABSTRACT FROM AUTHOR]

A method for high-scale 225Ac-production for medical application from a massive metallic 232Th-target irradiated with 160 MeV-protons is described. The target was made of a metallic Th disk of few mm thickness encapsulated in Nb shell using diffusion welding that provided effective target cooling under an intensive proton beam. Chemical processing started with selectively dissolving Nb and Th in mixtures of HF and HNO3 of different concentrations. The further chemical treatment included two sequential extractions of Th(IV) with di(2-ethylhexyl)orthophoshoric acid (HDEHP) and purification of Ac by extraction chromatography with DGA-, LN- and TRU-resins. The "end-to-start" technique, where the eluate of the column filled with one sorbent serves as the eluent for the column with next sorbent, was realized. The achieved total chemical yield of 225Ac was 87% and radionuclidic purity was better than 99.8% (excepting 0.1–0.2% 227Ac generated at the end of irradiation). The presented method can provide a hundred GBq of 225Ac in one irradiation run. [ABSTRACT FROM AUTHOR]

Pyridinium cesium cobalt nitrate, (PyH)CsCo2(NO3)6, obtained from a nitric acid solution crystallizes in the orthorhombic space group Pnma with unit cell parameters a = 8.6905(14) Å, b = 11.9599(18) Å, c = 18.386(3) Å, V = 1911.0(5) Å3, and Z = 4. It consists of [Co(NO3)3]− layers, in which each Co2+ ion is connected with four monodentate bridging NO3-groups and one bidentate terminal NO3-group, forming a corrugated rectangular net. Magnetization and specific heat measurements show that (PyH)CsCo2(NO3)6 undergoes a long-range canted antiferromagnetic ordering in two steps at TC1 = 5.0 K and TC2 = 2.6 K. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization measured for (PyH)CsCo2(NO3)6 show that it is an Ising antiferromagnet. In support of these observations, our DFT + U + SOC calculations show that the Co2+ ions of (PyH)CsCo2(NO3)6 have an easy-axis magnetic anisotropy with preferred spin orientation along the b-axis. To a first approximation, the spin lattice of (PyH)CsCo2(NO3)6 is a weakly alternating Ising antiferromagnetic chain (J1/J2 ∼ 0.85), and these chains interact weakly (J3/J2 ∼ 0.07) to form a rectangular Ising antiferromagnetic lattice. In agreement with the prediction for a rectangular Ising antiferromagnet by Onsager, (PyH)CsCo2(NO3)6 undergoes a long-range antiferromagnetic ordering. [ABSTRACT FROM AUTHOR]

We prepared a new compound, Co3(SeO3)(SeO4)(OH)2, having layers in a kagomé-like arrangement of Co2+ (spin S = 3/2) ions. This phase crystallizes in the orthorhombic space group Pnma (62) with unit cell parameters a = 11.225(9) Å, b = 6.466(7) Å and c = 11.530(20) Å. Its layers, parallel to the ab-plane, are made up of Co1O5 square pyramids and Co2O6 and Co3O6 octahedra. As the temperature is lowered, Co3(SeO3)(SeO4)(OH)2 undergoes three successive magnetic transitions at 27.5, 19.4 and 8.1 K, and the magnetization of Co3(SeO3)(SeO4)(OH)2 measured at 2.4 K exhibits a 1/3-magnetization plateau between 7.8 and 19.9 T. The H–T magnetic phase diagram constructed for Co3(SeO3)(SeO4)(OH)2 from ac and dc magnetic susceptibility, specific heat and magnetization measurements contains three magnetic phases I, II and III. Phase I is antiferromagnetic, while phases II and III are ferrimagnetic and responsible for the 1/3-magnetization plateau. To interpret these complex magnetic properties, we identified the correct spin lattice for Co3(SeO3)(SeO4)(OH)2 by evaluating its intralayer and interlayer spin exchanges based on spin-polarized DFT+U calculations. [ABSTRACT FROM AUTHOR]

The missing member of the rosiaite family, CoGeTeO6, was synthesized by mild ion-exchange reactions and characterized by magnetization M and specific heat Cp measurements. It exhibits a successive short- and long-range magnetic ordering at Tshort-range ≈ 45 K and TN = 15 K, respectively. Based on these measurements, the magnetic H–T phase diagram was established, showing two antiferromagnetic phases separated by a spin-flop transition. The reason why the pronounced short-range correlation occurs at a temperature nearly three times higher than TN was found by evaluating the Co–O⋯O–Co exchange interactions using energy-mapping analysis. Although CoGeTeO6 has a layered structure, its magnetic structure consists of three-dimensional antiferromagnetic lattices made up of rhombic boxes of Co2+ ions. The experimental data obtained at high temperatures agree well with the computational results by treating the Co2+ ions of CoGeTeO6 as S = 3/2 ions, but the heat capacity and magnetization data were obtained at low temperatures by treating the Co2+ ion as a Jeff = 1/2 ion. [ABSTRACT FROM AUTHOR]

Anhydrous copper tellurite sulfate, Cu3TeO3(SO4)2, has been synthesized via vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization M, magnetic susceptibility χ, specific heat Cp and X-band electron spin resonance, a long-range antiferromagnetic order at TN = 13 K and an H–T magnetic phase diagram have been established. One-third of Cu2+ ions were found to form magnetically silent dimers. A peak in dielectric permittivity ε, which accompanies the Néel order, allows considering Cu3TeO3(SO4)2 as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters. [ABSTRACT FROM AUTHOR]

The iron(III) anionic complex based on a pyruvic acid thiosemicarbazone ligand with the lithium cation Li[FeIII(thpy)2]·3H2O (1) has been synthesized and characterized by FTIR spectroscopy, powder and single crystal X-ray diffraction, direct current magnetic susceptibility measurements, and 57Fe Mössbauer spectroscopy. Moreover, the molecular structure of the [Fe(thpy)2]− anion has been determined for the first time. The [Fe(thpy)2]− units in the triclinic P1¯ lattice of 1 are assembled into layers parallel to the bc plane. The Li+ cations and water molecules are located between the layers and the structure is stabilized by hydrogen bonding. The [Fe(thpy)2]− anions form interconnected dimer pairs through hydrogen bonds and short contacts with Fe⋯Fe separation of 6.7861(4) Å. According to dc magnetic measurements, compound 1 demonstrates an incipient spin-crossover transition from the LS (S = 1/2) to the HS (S = 5/2) state above 250 K. The Bleaney–Bowers equation for a model of an isolated LS dimer with a mean-field correction was applied to fit the experimental data of magnetic susceptibility dependence on temperature in the temperature range of 2–250 K. The intra-dimer J1 = −1.79(1) K and inter-dimer J2 = −0.24(3) K antiferromagnetic coupling constants were defined. The analysis of the 57Fe Mössbauer spectra at 80 K and 296 K confirms the presence of the shortened distances between the iron nuclei. Moreover, the influence of the lithium cation on the stabilization of the LS state was shown for the [Fe(thpy)2]− anion. BS-DFT calculations for the optimized structure of two isolated [Fe(thpy)2]− anions also correctly predict a weak exchange J1(calc) = −0.92 K. DFT calculations revealed the OPBE (GGA-type) functional that correctly predicts the spin-crossover transition for the iron(III) thpy compounds. Besides, the effect of the N2O4, N2S2O2, and N2Se2O2 coordination environments on the energy stabilization of the LS state of iron(III) anionic thpy complexes was noted as well. [ABSTRACT FROM AUTHOR]

We prepared Cs2Cu3(SeO3)4·2H2O composed of Cu2+ ions at square-planar coordination sites and characterized its structural and magnetic properties, to show that Cs2Cu3(SeO3)4·2H2O is a ferrimagnet exhibiting a highly anisotropic 1/3-magnetization plateau. This unprecedented anisotropy in a magnetization plateau is the consequence of three effects, namely, the orthogonal arrangements of the corner-sharing CuO4 square planes, the nearest-neighbour antiferromagnetic exchange, and the anisotropic g-factor of the Cu2+ ions at square-planar coordination sites. By analyzing the topology of magnetic bonding, we found why magnetic plateaus are observed only for certain ferrimagnets and antiferromagnets. [ABSTRACT FROM AUTHOR]

A mixed-valence compound Pb2Cu10O4(SeO3)4Cl7 has a complex structure consisting of one nonmagnetic Cu+ (S = 0) ion and four nonequivalent magnetic Cu2+ (S = 1/2) ions. It exhibits antiferromagnetic ordering at TN = 10.2 K. At a temperature below TN, a sequence of spin-flop transition at Bspin-flop = 1.3 T and 1/3 plateau formation at Bspin-flip = 4.4 K is observed in the magnetization curve M(B). The 1/3 magnetization plateau persists at least up to 53.5 T. The spin exchanges of Pb2Cu10O4(SeO3)4Cl7 evaluated by performing energy-mapping analysis based on DFT+U calculations show that the magnetic properties of Pb2Cu10O4(SeO3)4Cl7 are described by the (Cu2+)7 cluster of corner-sharing (Cu2+)4 tetrahedra, and that each (Cu2+)7 cluster has a S = 3/2 spin arrangement in the ground state. The 1/3 magnetization plateau observed for Pb2Cu10O4(SeO3)4Cl7 is explained by the field-induced flip of every second (Cu2+)7 cluster within a unit cell. [ABSTRACT FROM AUTHOR]

Single crystals of a novel phase, potassium manganese silicate hydrate, K3Mn4Si10O24.33(H2O,OH)3, doped with B and V, were obtained under hydrothermal conditions and studied using scanning electron microscopy, microprobe analysis and low temperature synchrotron X-ray diffraction. The title structure represents an original silicate framework assembled from layers with various n-membered SiO4 rings that restrict channels open in the [001] direction. The corrugated chains of face-sharing MnO6 octahedra are incorporated into the space between "pendant" vertices of the tetrahedra framing 12-membered windows. This is the first example of combining two topologically different trimeric clusters of octahedra sharing faces into a single construction. The framework channels with 5- and 6-membered windows incorporate K atoms, and H2O molecules are located in the channels with 7-membered openings. We assume that the stability of this crystal structure is due to the partial substitution of Mn for V and Si for B. The magnetic subsystem in the title compound represents a rare case of the quasi-one-dimensional arrangement of MnO6 octahedra forming sawtooth-like chains. Measurements of magnetization and heat capacity of K3Mn4Si10O24.33(H2O,OH)3/V,B indicate the absence of long-range order up to 2 K. Structural features of the K3Mn4Si10O24.33(H2O,OH)3/V,B allow supposing it as potential multifunctional material, electrochemically active and having properties of low-dimensional magnet. [ABSTRACT FROM AUTHOR]

Mononuclear Mn(III) cation spin-crossover complexes with Schiff base ligands 3,5-diF-sal2323 and 3,5-Br,F-sal2323 have been synthesized: [Mn(3,5-diF-sal2323)]BPh4 (1) and two polymorphic modifications (2 and 3) of [Mn(3,5-Br,F-sal2323)]BPh4. Their crystal structure and magnetic properties have been studied. The complex [Mn(3,5-diF-sal2323)]BPh4 exhibits a gradual and complete spin conversion with T1/2 = 141 K between high spin (S = 2) and low spin (S = 1) states. Two polymorphic modifications of the complex [Mn(3,5-Br,F-sal2323)]BPh4 have fundamentally different magnetic properties: one of the modifications (monoclinic, 2) shows a gradual and complete spin transition with T1/2 = 137 K, while the other (triclinic, 3) suggests a more abrupt and not complete spin transition at 22 K which is difficult to diagnose due to the competition with the zero-field splitting effects. The magneto-structural relationships were traced in comparison with dichloro-, dibromo- and mixed Br,Cl-substituted [Mn(3,5-R,R′- sal2323)] complexes with tetraphenylborate anions. [ABSTRACT FROM AUTHOR]

We report the synthesis, crystal structure and magnetic properties of the new heptacoordinated mononuclear erbium(III) complex (Et3NH)[Er(H2DAPS)Cl2] (H4DAPS = 2,6-diacetylpyridine bis-(salicylhydrazone)) (1). The coordination polyhedron around the Er(III) ion features a slightly distorted pentagonal bipyramid formed by the pentagonal N3O2 chelate ring of the H2DAPS ligand in the equatorial plane and two apical chloride ligands. Detailed high-frequency/high-field electron paramagnetic resonance (HF-EPR) studies of 1 result in the precise determination of the crystal field (CF) splitting energies (0, 290 and 460 GHz) and effective g-values of the three lowest Kramers doublets (KDs) of the Er(III) ion. The obtained HF-EPR data are in good agreement with the results from CF analysis for the Er(III) ion based on the simulation of the dc magnetic data of 1. The results from dynamic susceptibility measurements indicate that there is no slow relaxation of magnetisation behaviour. This observation is discussed in terms of the electronic structure of 1 obtained from experimental and theoretical results. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of structure and magnetic properties of the quasi-octahedral complex (pipH2)[Co(TDA)2] 2H2O (I), (pipH22+ = piperazine dication, TDA2− = thiodiacetic anion) are described. X-ray diffraction studies reveal the first coordination sphere of the Co(II) ion, consisting of two chelating tridentate TDA ligands with a mixed sulfur–oxygen strongly elongated octahedral coordination environment. SQUID magnetometry, frequency-domain Fourier-transform (FD-FT) THz-EPR spectroscopy, and high-level ab initio SA-CASSCF/NEVPT2 quantum chemical calculations reveal a strong "easy-plane" type magnetic anisotropy (D ≈ +54 cm−1) of complex I. The complex shows field-induced slow relaxation of magnetization at an applied DC field of 1000 Oe. [ABSTRACT FROM AUTHOR]

Single crystals of dinickel diphosphate dihydrate, Ni2(H2O)2[P2O7], have been synthesized by a hydrothermal method. Its structure was refined in the monoclinic P21/n space group (unit cell parameters a = 6.2517(1) Å, b = 13.7892(3) Å, c = 7.2894(2) Å, β = 94.507(2)°, V = 626.45(2) Å3, and Z = 4) based on low-temperature X-ray diffraction data until R – 0.016. Corrugated chains of NiO5(H2O) octahedra sharing edges are aligned in the [101¯] direction. They are linked into a three-dimensional framework through diphosphate groups and hydrogen bonds. A detailed crystal chemical analysis of the family Me2(H2O)2[X2O7] revealed correlations between the unit-cell parameters of the isotypic transition metal phosphates and arsenates, their structural features and the sizes of structure forming cations. Despite the isolation of the cis and trans edge-sharing infinite zigzag chains of Ni-centered octahedra from each other no pronounced low dimensionality is seen in the magnetic response of Ni2(H2O)2[P2O7]. The magnetic susceptibility χ evidences a short range correlation maximum at Tmax = 11.9 K accompanied by the onset of long-range magnetic order at TN = 9.4 K. Below TN, the title compound exhibits the features of an archetype three-dimensional easy-axis antiferromagnet which experiences a sequence of spin–flop and spin–flip phase transitions. Basing on specific heat Cp and magnetization M studies, the magnetic phase diagram of Ni2(H2O)2[P2O7] has been established. [ABSTRACT FROM AUTHOR]

A series of three mononuclear pentagonal-bipyramidal V(III) complexes with the equatorial pentadentate N3O2 ligand (2,6-diacethylpyridinebis(benzoylhydrazone), H2DAPBH) in the different charge states (H2DAPBH0, HDAPBH1−, DAPBH2−) and various apical ligands (Cl−, CH3OH, SCN−) were synthesized and characterized structurally and magnetically: [V(H2DAPBH)Cl2]Cl·C2H5OH (1), [V(HDAPBH)(NCS)2]·0.5CH3CN·0.5CH3OH (2) and [V(DAPBH)(CH3OH)2]Cl·CH3OH (3). All three complexes reveal paramagnetic behavior, resulting from isolated S = 1 spins with positive zero-field splitting energy expected for the high-spin ground state of the V3+ (3d2) ion in a PBP coordination. Detailed high-field EPR measurements for compound 3 show that its magnetic properties are best described by using the spin Hamiltonian with the positive ZFS energy (D = +4.1 cm−1) and pronounced dimer-like antiferromagnetic spin coupling (J = −1.1 cm−1). Theoretical analysis based on superexchange calculations reveals that the long-range spin coupling between distant V3+ ions (8.65 Å) is mediated through π-stacking contacts between the planar DAPBH2− ligands of two neighboring [V(DAPBH)(CH3OH)2]+ complexes. [ABSTRACT FROM AUTHOR]

Phase-pure orthorhombic compositions at a Ln/Mo ratio ∼ 5.2–5.7 (Ln = Gd, Dy, Ho) have been obtained for the first time by prolonged (40–160 h) heat treatment of mechanically activated 5Ln2O3 + 2MoO3 (Ln = Gd, Dy, Ho) oxide mixtures at 1200 °C. Although the starting Ln : Mo ratio was 5 : 1 (Ln10Mo2O21 (Ln = Dy, Ho)), it changed slightly in the final product due to the volatility of molybdenum oxide at 1200 °C (40–160 h) (ICP-MS analysis). Brief high-temperature firing (1600 °C, 3 h) of 5Ln2O3 + 2MoO3 (Ln = Gd, Dy, Ho) oxide mixtures leads to the formation of phase-pure fluorites with compositions close to Ln10Mo2O21 (Ln = Gd, Dy, Ho). Gd10Mo2O21 molybdate seems to undergo an order–disorder (orthorhombic–fluorite) phase transition in the range of 1200–1600 °C. For the first time, using the neutron diffraction method, it was shown that low-temperature phases with a Ln/Mo ratio ∼ 5.2–5.7 (Ln = Gd, Dy, Ho) have an orthorhombic structure rather than a tetragonal structure. Proton contribution to the total conductivity of Ln10Mo2O21 (Ln = Gd, Dy, Ho) fluorites and gadolinium and dysprosium orthorhombic phases in a wet atmosphere was observed for the first time. In both orthorhombic and fluorite phases, the total conductivity in wet air decreases with decreasing lanthanide ionic radii. In a wide temperature range, the compounds under study exhibit paramagnetic behaviour. However, the orthorhombic phases of Dy and Ho compounds reach the antiferromagnetic state at 2.4 K and 2.6 K, respectively. [ABSTRACT FROM AUTHOR]

Antiferromagnetic PbMnTeO6, also known as mineral kuranakhite, has been reported recently to have all three cations in trigonal prismatic coordination, which is extremely unusual for both Mn(4+) and Te(6+). In this work, the phase was reproduced with the same lattice parameters and Néel temperature TN = 20 K. However, powder neutron diffraction unambiguously determined octahedral (trigonal antiprismatic) coordination for all cations within the chiral space group P312. The same symmetry was proposed for SrMnTeO6 and PbGeTeO6, instead of the reported space groups P62m and P31m, respectively. PbMnTeO6 was found to be a robust antiferromagnet with an assumingly substantial scale of exchange interactions since the Néel temperature did not show any changes in external magnetic fields up to 7 T. The determined effective magnetic moment μeff = 3.78μB was in excellent agreement with the numerical estimation using the effective g-factor g = 1.95 directly measured here by electron spin resonance (ESR). Both specific heat and ESR data indicated the two-dimensional character of magnetism in the compound under study. The combination of chirality with magnetic order makes PbMnTeO6 a promising material with possible multiferroic properties. [ABSTRACT FROM AUTHOR]

Li3Co2SbO6 is prepared by molten salt ion exchange and its structure refined by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na precursor. Monoclinic rather than trigonal symmetry of Na3Co2SbO6 is directly demonstrated for the first time by peak splitting in the high-resolution synchrotron XRD pattern. The long-range antiferromagnetic order is established at TN ≈ 6.7 K and 9.9 K in Na3Co2SbO6 and Li3Co2SbO6, respectively, confirmed by both the magnetic susceptibility and specific heat. Spin-wave analysis of specific heat data indicates the presence of 3D AFM magnons in Na3Co2SbO6 and 2D AFM magnons in Li3Co2SbO6. The field dependence of the magnetization almost reaches saturation in moderate magnetic fields up to 9 T and demonstrates characteristic features of magnetic field induced spin-reorientation transitions for both A3Co2SbO6 (A = Na, Li). Overall thermodynamic studies show that the magnetic properties of both compounds are very sensitive to an external magnetic field, thus predicting a non-trivial ground state with a rich magnetic phase diagram. The ground state spin configuration of Li3Co2SbO6 has been determined by low-temperature neutron powder diffraction. It represents a ferromagnetic arrangement of moments in the honeycomb layers with antiferromagnetic coupling between adjacent layers. [ABSTRACT FROM AUTHOR]

The iron(iii) complex [Fe(Hsemsal)(semsal)]·3H2O (1) (H2semsal – salicylaldehyde semicarbazone) has been synthesized and characterized by powder and single crystal X-ray diffraction, and magnetic susceptibility measurements. Crystal structure analysis showed that the complex forms neat stacks stabilized by hydrogen-bonding through water molecules and π–π interactions between phenolate rings of ligands. The complex does not exhibit spin-crossover phenomena and remains in the high-spin state down to 2 K. DFT calculations were performed for a series of neutral Fe(iii) complexes, and the influence of the N2S2O2, N2Se2O2 and N2O4 coordination environment on the spin transition in these complexes was traced. The effect of substituents in the benzene ring of salicylaldehyde on the stabilization of the HS or LS states in complexes of this type was analyzed. [ABSTRACT FROM AUTHOR]

A coordination compound with the composition [CoLCl2]·H2O (L = bis-condensation product of diacetyl and 2-hydrazinyl-4,6-dimethylpyrimidine) was synthesized, in which the Co(II) ion was hexacoordinated. Under applied DC fields, this compound exhibited single-ion magnet behavior. Two relaxation processes were observed when increasing the applied magnetic field from 1000 to 3200 Oe. The first relaxation (high-frequency) was observed both at 1000 Oe and 3200 Oe, while the second relaxation was only registered under a field of 3200 Oe at low frequencies (<1 Hz) and low temperatures (<5 K). Modeling of the magnetic DC properties using the Griffith Hamiltonian accompanied by quantum chemical calculations revealed easy-axis-type magnetic anisotropy with weak rhombic contributions. [ABSTRACT FROM AUTHOR]

Ion-exchange treatment of Na2SnTeO6 in molten salt mixtures resulted in rosiaite (PbSb2O6)-related MnSnTeO6. Its crystal structure was refined by the Rietveld method. Of the three possible models of Sn/Te distribution, the disordered model (P3̅1m, a = 5.23093(11) Å, c = 4.62430(16) Å) was preferred based on bond distances. However, it is supposed that each individual (SnTeO6)2− layer retains complete ordering of the precursor and the apparent disorder is only due to stacking faults. Magnetic studies have shown that MnSnTeO6 orders antiferromagnetically at Neél temperature TN = 9.8 K. The effective magnetic moment reasonably agrees with theoretical estimations assuming high-spin configuration of Mn2+ (S = 5/2). Electron spin resonance reveals spin dynamics in accordance with antiferromagnetic ordering. Moreover, critical broadening of ESR linewidth indicates the low-dimensional type of exchange interactions. Based on the temperature and field-dependent magnetization studies, the magnetic phase diagram of the new compound was constructed. [ABSTRACT FROM AUTHOR]

The manganese end member of triplite–triploidite series of compounds, Mn2(PO4)OH, is synthesized by a hydrothermal method. Its crystal structure is refined in the space group P21/c with a = 12.411(1) Å, b = 13.323(1) Å, c = 10.014(1) Å, β = 108.16(1), V = 1573.3 Å3, Z = 8, and R = 0.0375. Evidenced in measurements of magnetization M and specific heat Cp, Mn2(PO4)OH reaches a long range antiferromagnetic order at TN = 4.6 K. As opposed to both triplite Mn2(PO4)F and triploidite-type Co2(PO4)F, the title compound is magnetically frustrated being characterized by the ratio of Curie–Weiss temperature Θ to Néel temperature TN of about 20. The large value of frustration strength ☋Θ☋/TN stems from the twisted saw tooth chain geometry of corner sharing triangles of Mn polyhedra, which may be isolated within tubular fragments of a triploidite crystal structure. [ABSTRACT FROM AUTHOR]

MSb2O6 compounds (M = Mg, Co, Ni, Cu, Zn) are known in the tetragonal trirutile forms, slightly distorted monoclinically with M = Cu due to the Jahn–Teller effect. In this study, using a low-temperature exchange reaction between ilmenite-type NaSbO3 and molten MSO4–KCl (or MgCl2–KCl) mixtures, these five compositions were prepared for the first time as trigonal layered rosiaite (PbSb2O6)-type phases. Upon heating, they irreversibly transform to the known phases via amorphous intermediates, in contrast to previously studied isostructural MnSb2O6, where the stable phase is structurally related to the metastable phase. The same method was found to be applicable for preparing stable rosiaite-type CdSb2O6. The formula volumes of the new phases show an excellent correlation with the ionic radii (except for M = Cu, for which a Jahn–Teller distortion is suspected) and are 2–3% larger than those for the known forms although all coordination numbers are the same. The crystal structure of CoSb2O6 was refined via the Rietveld method: P3̅1m, a = 5.1318(3) Å, and c = 4.5520(3) Å. Compounds with M = Co and Ni antiferromagnetically order at 11 and 15 K, respectively, whereas the copper compound does not show long-range magnetic order down to 1.5 K. A comparison between the magnetic behavior of the metastable and stable polymorphs was carried out. FeSb2O6 could not be prepared because of the 2Fe2+ + Sb5+ = 2Fe3+ + Sb3+ redox reaction. This electron transfer produces an additional 5s2 shell for Sb and results in a volume increase. A comparison of the formula volume for the stable mixture FeSbO4 + 0.5Sb2O4 with that extrapolated for FeSb2O6 predicted that the trirutile-type FeSb2O6 can be stabilized at high pressures. [ABSTRACT FROM AUTHOR]

The novel borophosphate Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] was prepared under hydrothermal conditions at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data obtained from a non-merohedral twin and refined against F2 to R = 0.057. The compound crystallizes in the orthorhombic space group Pbcn, with unit-cell parameters a = 20.076(2) Å, b = 9.151(1) Å, c = 12.257(1) Å, V = 2251.8(2) Å3, and Z = 4. The title compound is the first example of a borophosphate with manganese ions adopting both octahedral and tetrahedral coordinations. Its unique crystal structure is formed by borophosphate slabs and chains of Mn2+-centered polyhedra sharing edges and vertices. These 2D and 1D fragments interconnect into a framework with open channels that accommodate Rb+ cations and water molecules. Topological relationships between borophosphates built from three-membered rings of two borate and one phosphate tetrahedra sharing oxygen vertices, amended by additional PO4 and HPO4 tetrahedra, are discussed. The temperature dependence of the magnetic susceptibility of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] reveals predominant antiferromagnetic exchange interactions and the high-temperature effective magnetic moment corresponding to the high-spin S = 5/2 state of Mn2+ ions. At 12.5 K, a magnetic transition is evidenced by ac-susceptibility and specific heat measurements. A spin-trimer model with the leading exchange interaction J∼ 3.2 K is derived from density-functional band-structure calculations and accounts for all experimental observations. [ABSTRACT FROM AUTHOR]

We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin–flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co–Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co2+ ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite. [ABSTRACT FROM AUTHOR]

The novel phosphate RbCuAl(PO4)2 was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F2 to R = 0.026. The compound crystallizes in the monoclinic space group P21/c, with unit-cell parameters a = 5.0723(8) Å, b = 14.070(2) Å, c = 9.352(1) Å, β = 100.41(1), V = 656.4(2) Å3, and Z = 4. The crystal structure is based on an open 3D aluminophosphate framework built by AlO5 bipyramids and PO4 tetrahedra sharing oxygen vertices. Channels in the [100] and [001] directions accommodate Rb+ cations and chains of Cu-centered octahedra alternatively sharing cis- and trans-edges. The new phase is characterized by the structure type established for isotypic iron phosphates KMFe(PO4)2, where M = Fe/Ni, Ni, Mg or Co. It also shows topological relationships with Pb2Ni(PO4)2 and Fe3+Fe2+0.5(H2O)2(HPO4)2 structures. The RbCuAl(PO4)2 exhibits rather peculiar physical properties evidenced in specific heat and magnetization measurements. It releases a significant part of magnetic entropy well above the Neel temperature TN = 10.5 K and possesses a spontaneous magnetic moment at lower temperatures. The origin of the spontaneous moment is ascribed to the canting of a pristine antiferromagnetic structure due to the interchain Dzyaloshinskii–Moriya exchange interaction. [ABSTRACT FROM AUTHOR]

Highly homogeneous mullite-type solid solutions Bi2Fe4−xCrxO9 (x = 0.5, 1, 1.2) were synthesized using a soft chemistry technique followed by a solid-state reaction in Ar. The crystal structure of Bi2Fe3CrO9 was investigated using X-ray and neutron powder diffraction, transmission electron microscopy and 57Fe Mössbauer spectroscopy (S.G. Pbam, a = 7.95579(9) Å, b = 8.39145(9) Å, c = 5.98242(7) Å, RF(X-ray) = 0.022, RF(neutron) = 0.057). The ab planes in the structure are tessellated with distorted pentagonal loops built up by three tetrahedrally coordinated Fe sites and two octahedrally coordinated Fe/Cr sites, linked together in the ab plane by corner-sharing forming a pentagonal Cairo lattice. Magnetic susceptibility measurements and powder neutron diffraction show that the compounds order antiferromagnetically (AFM) with the Néel temperatures decreasing upon increasing the Cr content from TN∼ 250 K for x = 0 to TN∼ 155 K for x = 1.2. The magnetic structure of Bi2Fe3CrO9 at T = 30 K is characterized by a propagation vector k = (1/2,1/2,1/2). The tetrahedrally coordinated Fe cations form singlet pairs within dimers of corner-sharing tetrahedra, but spins on the neighboring dimers are nearly orthogonal. The octahedrally coordinated (Fe,Cr) cations form antiferromagnetic up–up–down–down chains along c, while the spin arrangement in the ab plane is nearly orthogonal between nearest neighbors and collinear between second neighbors. The resulting magnetic structure is remarkably different from the one in pure Bi2Fe4O9 and features several types of spin correlations even on crystallographically equivalent exchange that may be caused by the simultaneous presence of Fe and Cr on the octahedral site. [ABSTRACT FROM AUTHOR]

The novel phase Na2−xCo6(OH)3[HPO4][Hx/3PO4]3 (x≈ 1.1) was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F2 to R = 0.052, including positions of all hydrogen atoms. The compound crystallizes in the hexagonal space group P63mc, with unit-cell parameters a = 12.630(3) Å, c = 5.017(1) Å, V = 693.1(3) Å3, and Z = 2. The crystal structure is based on a 3D framework built from CoO6 octahedra and PO4 tetrahedra. Channels in the [001] direction accommodate columns of Na-centered octahedra sharing faces. The compound is a new structural representative of the topology shown by aluminosilicate mineral ellenbergerite and its numerous natural and synthetic varieties. Magnetic susceptibility measurements revealed a strong antiferromagnetic interaction and magnetic transition to low temperature spin-canted phase at TN = 44 K. The physical properties of the title compound are found to be very similar to those of the structurally related arsenate Co1−xCo6(OH)3[H2x/3AsO4]3[HAsO4] and vanadate Co7(OH)2(H2O)[VO4]4. [ABSTRACT FROM AUTHOR]

Low molecular weight organics (LMWO; e.g. acetate, propionate, lactate) can significantly impact the speciation and mobility of radionuclides in aqueous media. Natural clay rock formation, considered as a potential host rock for nuclear waste disposal, can contain a significant amount of organic matter. There are less thermodynamic data reported for the complexation of pentavalent actinides with LMWO, especially under elevated temperature conditions, relevant for assessing the long-term safety of disposal options for heat-producing high-level nuclear waste. In the present study, the complexation of Np(v) with propionate is studied using spectroscopic techniques in 0.5–4 M NaCl solutions by systematic variation of the ligand concentration and temperature. Slope analysis shows the formation of the 1 : 1 NpO2-propionate complex (NpO2Prop). The local structure of the NpO2-propionate complex is determined by extended X-ray absorption fine structure spectroscopy, the results of which suggest that propionate binds to Np(v) in a bidentate mode. Using the specific ion interaction theory (SIT), the stability constant at zero ionic strength and 25 °C is determined as log β°1,1 = 1.26 ± 0.03. The stability constants increase continuously with increasing temperature between 20 and 85 °C. The log β0 values are linearly correlated with the reciprocal temperature, indicating ΔrHSTACKABOVE0/ABOVEBELOWm/BELOW/STACK = const. and ΔrCSTACKABOVE0/ABOVEBELOWp,m/BELOW/STACK = 0, allowing the calculation of ΔrHSTACKABOVE0/ABOVEBELOWm/BELOW/STACK and ΔrSSTACKABOVE0/ABOVEBELOWm/BELOW/STACK for the formation of the NpO2-propionate complex using the integrated van't Hoff equation. The thermodynamic evaluation indicates that the reaction is endothermic and entropy driven. [ABSTRACT FROM AUTHOR]

The solid solution Cs2-xRbxSnCu3F12 (x = 0, 0.5, 1.0, 1.5) has been investigated crystallographically between 100 and 300 K using synchrotron X-ray powder diffraction and, in the case of x = 0, neutron powder diffraction. For Cs2RbxSnCu3F12 (x = 0), there is a structural transition from the previously reported room temperature rhombohedral symmetry (R3m) to monoclinic (P2n) symmetry at 170 K. This transformation is repeated for the x = 0.5 composition, but with an increased transition temperature of 250 K. For x = 1.0 the monoclinic phase is found at 300 K, suggesting that the transition temperature is increased even further. For x = 1.5 a different behaviour, more akin to that previously reported for Cs2RbxSnCu3F12, is found: a single phase transition between rhombohedral symmetry (R3) and triclinic symmetry (P1) is found at 280 K. In agreement with previous single crystal studies, Cs2RbxSnCu3F12 powder exhibits strong antiferromagnetic interactions (Θ -268 K) and long-range magnetic order at TN 19.3 K. The finite magnetic moment observed for T < TN might be explained by a Dzyaloshinskii--Moriya interaction, due to the lowering of symmetry from rhombohedral to monoclinic, which was not suggested in the earlier single crystal study. [ABSTRACT FROM AUTHOR]

Pyridinium cesium cobalt nitrate, (PyH)CsCo2(NO3)6, obtained from a nitric acid solution crystallizes in the orthorhombic space group Pnma with unit cell parameters a = 8.6905(14) Å, b = 11.9599(18) Å, c = 18.386(3) Å, V = 1911.0(5) Å3, and Z = 4. It consists of [Co(NO3)3]− layers, in which each Co2+ ion is connected with four monodentate bridging NO3-groups and one bidentate terminal NO3-group, forming a corrugated rectangular net. Magnetization and specific heat measurements show that (PyH)CsCo2(NO3)6 undergoes a long-range canted antiferromagnetic ordering in two steps at TC1 = 5.0 K and TC2 = 2.6 K. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization measured for (PyH)CsCo2(NO3)6 show that it is an Ising antiferromagnet. In support of these observations, our DFT + U + SOC calculations show that the Co2+ ions of (PyH)CsCo2(NO3)6 have an easy-axis magnetic anisotropy with preferred spin orientation along the b-axis. To a first approximation, the spin lattice of (PyH)CsCo2(NO3)6 is a weakly alternating Ising antiferromagnetic chain (J1/J2 ∼ 0.85), and these chains interact weakly (J3/J2 ∼ 0.07) to form a rectangular Ising antiferromagnetic lattice. In agreement with the prediction for a rectangular Ising antiferromagnet by Onsager, (PyH)CsCo2(NO3)6 undergoes a long-range antiferromagnetic ordering. [ABSTRACT FROM AUTHOR]

Single crystals of dinickel diphosphate dihydrate, Ni2(H2O)2[P2O7], have been synthesized by a hydrothermal method. Its structure was refined in the monoclinic P21/n space group (unit cell parameters a = 6.2517(1) Å, b = 13.7892(3) Å, c = 7.2894(2) Å, β = 94.507(2)°, V = 626.45(2) Å3, and Z = 4) based on low-temperature X-ray diffraction data until R – 0.016. Corrugated chains of NiO5(H2O) octahedra sharing edges are aligned in the [101¯] direction. They are linked into a three-dimensional framework through diphosphate groups and hydrogen bonds. A detailed crystal chemical analysis of the family Me2(H2O)2[X2O7] revealed correlations between the unit-cell parameters of the isotypic transition metal phosphates and arsenates, their structural features and the sizes of structure forming cations. Despite the isolation of the cis and trans edge-sharing infinite zigzag chains of Ni-centered octahedra from each other no pronounced low dimensionality is seen in the magnetic response of Ni2(H2O)2[P2O7]. The magnetic susceptibility χ evidences a short range correlation maximum at Tmax = 11.9 K accompanied by the onset of long-range magnetic order at TN = 9.4 K. Below TN, the title compound exhibits the features of an archetype three-dimensional easy-axis antiferromagnet which experiences a sequence of spin–flop and spin–flip phase transitions. Basing on specific heat Cp and magnetization M studies, the magnetic phase diagram of Ni2(H2O)2[P2O7] has been established. [ABSTRACT FROM AUTHOR]

Antiferromagnetic PbMnTeO6, also known as mineral kuranakhite, has been reported recently to have all three cations in trigonal prismatic coordination, which is extremely unusual for both Mn(4+) and Te(6+). In this work, the phase was reproduced with the same lattice parameters and Néel temperature TN = 20 K. However, powder neutron diffraction unambiguously determined octahedral (trigonal antiprismatic) coordination for all cations within the chiral space group P312. The same symmetry was proposed for SrMnTeO6 and PbGeTeO6, instead of the reported space groups P62m and P31m, respectively. PbMnTeO6 was found to be a robust antiferromagnet with an assumingly substantial scale of exchange interactions since the Néel temperature did not show any changes in external magnetic fields up to 7 T. The determined effective magnetic moment μeff = 3.78μB was in excellent agreement with the numerical estimation using the effective g-factor g = 1.95 directly measured here by electron spin resonance (ESR). Both specific heat and ESR data indicated the two-dimensional character of magnetism in the compound under study. The combination of chirality with magnetic order makes PbMnTeO6 a promising material with possible multiferroic properties. [ABSTRACT FROM AUTHOR]

Li3Co2SbO6 is prepared by molten salt ion exchange and its structure refined by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na precursor. Monoclinic rather than trigonal symmetry of Na3Co2SbO6 is directly demonstrated for the first time by peak splitting in the high-resolution synchrotron XRD pattern. The long-range antiferromagnetic order is established at TN ≈ 6.7 K and 9.9 K in Na3Co2SbO6 and Li3Co2SbO6, respectively, confirmed by both the magnetic susceptibility and specific heat. Spin-wave analysis of specific heat data indicates the presence of 3D AFM magnons in Na3Co2SbO6 and 2D AFM magnons in Li3Co2SbO6. The field dependence of the magnetization almost reaches saturation in moderate magnetic fields up to 9 T and demonstrates characteristic features of magnetic field induced spin-reorientation transitions for both A3Co2SbO6 (A = Na, Li). Overall thermodynamic studies show that the magnetic properties of both compounds are very sensitive to an external magnetic field, thus predicting a non-trivial ground state with a rich magnetic phase diagram. The ground state spin configuration of Li3Co2SbO6 has been determined by low-temperature neutron powder diffraction. It represents a ferromagnetic arrangement of moments in the honeycomb layers with antiferromagnetic coupling between adjacent layers. [ABSTRACT FROM AUTHOR]

MSb2O6 compounds (M = Mg, Co, Ni, Cu, Zn) are known in the tetragonal trirutile forms, slightly distorted monoclinically with M = Cu due to the Jahn–Teller effect. In this study, using a low-temperature exchange reaction between ilmenite-type NaSbO3 and molten MSO4–KCl (or MgCl2–KCl) mixtures, these five compositions were prepared for the first time as trigonal layered rosiaite (PbSb2O6)-type phases. Upon heating, they irreversibly transform to the known phases via amorphous intermediates, in contrast to previously studied isostructural MnSb2O6, where the stable phase is structurally related to the metastable phase. The same method was found to be applicable for preparing stable rosiaite-type CdSb2O6. The formula volumes of the new phases show an excellent correlation with the ionic radii (except for M = Cu, for which a Jahn–Teller distortion is suspected) and are 2–3% larger than those for the known forms although all coordination numbers are the same. The crystal structure of CoSb2O6 was refined via the Rietveld method: P3̅1m, a = 5.1318(3) Å, and c = 4.5520(3) Å. Compounds with M = Co and Ni antiferromagnetically order at 11 and 15 K, respectively, whereas the copper compound does not show long-range magnetic order down to 1.5 K. A comparison between the magnetic behavior of the metastable and stable polymorphs was carried out. FeSb2O6 could not be prepared because of the 2Fe2+ + Sb5+ = 2Fe3+ + Sb3+ redox reaction. This electron transfer produces an additional 5s2 shell for Sb and results in a volume increase. A comparison of the formula volume for the stable mixture FeSbO4 + 0.5Sb2O4 with that extrapolated for FeSb2O6 predicted that the trirutile-type FeSb2O6 can be stabilized at high pressures. [ABSTRACT FROM AUTHOR]

The novel borophosphate Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] was prepared under hydrothermal conditions at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data obtained from a non-merohedral twin and refined against F2 to R = 0.057. The compound crystallizes in the orthorhombic space group Pbcn, with unit-cell parameters a = 20.076(2) Å, b = 9.151(1) Å, c = 12.257(1) Å, V = 2251.8(2) Å3, and Z = 4. The title compound is the first example of a borophosphate with manganese ions adopting both octahedral and tetrahedral coordinations. Its unique crystal structure is formed by borophosphate slabs and chains of Mn2+-centered polyhedra sharing edges and vertices. These 2D and 1D fragments interconnect into a framework with open channels that accommodate Rb+ cations and water molecules. Topological relationships between borophosphates built from three-membered rings of two borate and one phosphate tetrahedra sharing oxygen vertices, amended by additional PO4 and HPO4 tetrahedra, are discussed. The temperature dependence of the magnetic susceptibility of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] reveals predominant antiferromagnetic exchange interactions and the high-temperature effective magnetic moment corresponding to the high-spin S = 5/2 state of Mn2+ ions. At 12.5 K, a magnetic transition is evidenced by ac-susceptibility and specific heat measurements. A spin-trimer model with the leading exchange interaction J∼ 3.2 K is derived from density-functional band-structure calculations and accounts for all experimental observations. [ABSTRACT FROM AUTHOR]

We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin–flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co–Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co2+ ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite. [ABSTRACT FROM AUTHOR]

The novel phosphate RbCuAl(PO4)2 was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F2 to R = 0.026. The compound crystallizes in the monoclinic space group P21/c, with unit-cell parameters a = 5.0723(8) Å, b = 14.070(2) Å, c = 9.352(1) Å, β = 100.41(1), V = 656.4(2) Å3, and Z = 4. The crystal structure is based on an open 3D aluminophosphate framework built by AlO5 bipyramids and PO4 tetrahedra sharing oxygen vertices. Channels in the [100] and [001] directions accommodate Rb+ cations and chains of Cu-centered octahedra alternatively sharing cis- and trans-edges. The new phase is characterized by the structure type established for isotypic iron phosphates KMFe(PO4)2, where M = Fe/Ni, Ni, Mg or Co. It also shows topological relationships with Pb2Ni(PO4)2 and Fe3+Fe2+0.5(H2O)2(HPO4)2 structures. The RbCuAl(PO4)2 exhibits rather peculiar physical properties evidenced in specific heat and magnetization measurements. It releases a significant part of magnetic entropy well above the Neel temperature TN = 10.5 K and possesses a spontaneous magnetic moment at lower temperatures. The origin of the spontaneous moment is ascribed to the canting of a pristine antiferromagnetic structure due to the interchain Dzyaloshinskii–Moriya exchange interaction. [ABSTRACT FROM AUTHOR]

We prepared an organically templated magnet, ( en H 2 ) 0.5 VPO 4 OH ( en H 2 = diprotonated ethylenediamine), hydrothermally and characterized its crystal structure by powder X-ray diffraction and Fourier-transform infrared spectroscopy, and its physical properties by magnetization, specific heat and nuclear magnetic resonance measurements and density functional theory calculations. ( en H 2 ) 0.5 VPO 4 OH consists of uniform chains of V 3+ (d 2 , S = 1) ions and exhibits Haldane magnetism with spin gap Δ = 59.3 K from the magnetic susceptibility χ ( T ) at μ 0 H P shift. The NMR data evidence the formation of a spin-glass state of unpaired μ 0 H = 9 T according to the 31 P shift. The NMR data evidence the formation of a spin-glass state of unpaired S = 1/2 spins at T S-G ≈ 3 K and indicate that the Haldane S = 1 spin chain segments are much longer in the organically templated magnet ( en H 2 ) 0.5 VPO 4 OH than in the ammonium counterpart NH 4 VPO 4 OH. The single-ion anisotropy D and the interchain exchange J ' in ( en H 2 ) 0.5 VPO 4 OH and NH 4 VPO 4 OH were estimated in density functional calculations to find them very weak compared to the intrachain exchange J .

Pyridinium cesium cobalt nitrate, (PyH)CsCo 2 (NO 3 ) 6 , obtained from a nitric acid solution crystallizes in the orthorhombic space group Pnma with unit cell parameters a = 8.6905(14) Å, b = 11.9599(18) Å, c = 18.386(3) Å, V = 1911.0(5) Å 3 , and Z = 4. It consists of [Co(NO 3 ) 3 ] - layers, in which each Co 2+ ion is connected with four monodentate bridging NO 3 -groups and one bidentate terminal NO 3 -group, forming a corrugated rectangular net. Magnetization and specific heat measurements show that (PyH)CsCo 2 (NO 3 ) 6 undergoes a long-range canted antiferromagnetic ordering in two steps at T C1 = 5.0 K and T C2 = 2.6 K. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization measured for (PyH)CsCo 2 (NO 3 ) 6 show that it is an Ising antiferromagnet. In support of these observations, our DFT + U + SOC calculations show that the Co 2+ ions of (PyH)CsCo 2 (NO 3 -axis. To a first approximation, the spin lattice of (PyH)CsCo 6 have an easy-axis magnetic anisotropy with preferred spin orientation along the b -axis. To a first approximation, the spin lattice of (PyH)CsCo 2 is a weakly alternating Ising antiferromagnetic chain ( 3 ) 6 is a weakly alternating Ising antiferromagnetic chain ( J 1 ∼ 0.07) to form a rectangular Ising antiferromagnetic lattice. In agreement with the prediction for a rectangular Ising antiferromagnet by Onsager, (PyH)CsCo J 2 ∼ 0.85), and these chains interact weakly ( J undergoes a long-range antiferromagnetic ordering.3 / J 2 ∼ 0.07) to form a rectangular Ising antiferromagnetic lattice. In agreement with the prediction for a rectangular Ising antiferromagnet by Onsager, (PyH)CsCo 2 (NO 3 ) 6 undergoes a long-range antiferromagnetic ordering.

We prepared a new compound, Co 3 (SeO 3 )(SeO 4 )(OH) 2 , having layers in a kagomé-like arrangement of Co 2+ (spin S = 3/2) ions. This phase crystallizes in the orthorhombic space group Pnma (62) with unit cell parameters a = 11.225(9) Å, b = 6.466(7) Å and c = 11.530(20) Å. Its layers, parallel to the ab -plane, are made up of Co1O 5 square pyramids and Co2O 6 and Co3O 6 octahedra. As the temperature is lowered, Co 3 (SeO 3 )(SeO 4 )(OH) 2 undergoes three successive magnetic transitions at 27.5, 19.4 and 8.1 K, and the magnetization of Co 3 (SeO 3 )(SeO 4 )(OH) 2 measured at 2.4 K exhibits a 1/3-magnetization plateau between 7.8 and 19.9 T. The  H - T  magnetic phase diagram constructed for Co 3 (SeO 3 )(SeO 4 )(OH) 2  from ac and dc magnetic susceptibility, specific heat and magnetization measurements contains three magnetic phases I, II and III. Phase I is antiferromagnetic, while phases II and III are ferrimagnetic and responsible for the 1/3-magnetization plateau. To interpret these complex magnetic properties, we identified the correct spin lattice for Co 3 (SeO 3 )(SeO 4 )(OH) 2 by evaluating its intralayer and interlayer spin exchanges based on spin-polarized DFT+ U calculations.

We prepared Cs 2 Cu 3 (SeO 3 ) 4 ·2H 2 O composed of Cu 2+ ions at square-planar coordination sites and characterized its structural and magnetic properties, to show that Cs 2 Cu 3 (SeO 3 ) 4 ·2H 2 O is a ferrimagnet exhibiting a highly anisotropic 1/3-magnetization plateau. This unprecedented anisotropy in a magnetization plateau is the consequence of three effects, namely, the orthogonal arrangements of the corner-sharing CuO 4 square planes, the nearest-neighbour antiferromagnetic exchange, and the anisotropic g -factor of the Cu 2+ ions at square-planar coordination sites. By analyzing the topology of magnetic bonding, we found why magnetic plateaus are observed only for certain ferrimagnets and antiferromagnets.

A mixed-valence compound Pb 2 Cu 10 O 4 (SeO 3 ) 4 Cl 7 has a complex structure consisting of one nonmagnetic Cu + ( S = 0) ion and four nonequivalent magnetic Cu 2+ ( S = 1/2) ions. It exhibits antiferromagnetic ordering at T = 10.2 K. At a temperature below N , a sequence of spin-flop transition at T N , a sequence of spin-flop transition at B spin-flop = 1.3 T and 1/3 plateau formation at B spin-flip = 4.4 K is observed in the magnetization curve M ( B ). The 1/3 magnetization plateau persists at least up to 53.5 T. The spin exchanges of Pb 2 Cu 10 O 4 (SeO 3 ) 4 Cl 7 evaluated by performing energy-mapping analysis based on DFT+U calculations show that the magnetic properties of Pb 2 Cu 10 O 4 (SeO 3 ) 4 Cl 7 are described by the (Cu 2+ ) 7 cluster has a 2+ ) 4 tetrahedra, and that each (Cu 2+ ) 7 cluster has a S = 3/2 spin arrangement in the ground state. The 1/3 magnetization plateau observed for Pb 2 Cu 10 O 4 (SeO 3 cluster within a unit cell.4 Cl 7 is explained by the field-induced flip of every second (Cu 2+ ) 7 cluster within a unit cell.

Synthesis and characterization of structure and magnetic properties of the quasi-octahedral complex (pipH 2 )[Co(TDA) 2 ] 2H 2 O (I), (pipH 2 2+ = thiodiacetic anion) are described. X-ray diffraction studies reveal the first coordination sphere of the Co(II) ion, consisting of two chelating tridentate TDA ligands with a mixed sulfur-oxygen strongly elongated octahedral coordination environment. SQUID magnetometry, frequency-domain Fourier-transform (FD-FT) THz-EPR spectroscopy, and high-level 2- SA-CASSCF/NEVPT2 quantum chemical calculations reveal a strong "easy-plane" type magnetic anisotropy ( ab initio SA-CASSCF/NEVPT2 quantum chemical calculations reveal a strong "easy-plane" type magnetic anisotropy ( D ≈ +54 cm -1 ) of complex I. The complex shows field-induced slow relaxation of magnetization at an applied DC field of 1000 Oe.

Phase-pure orthorhombic compositions at a Ln/Mo ratio ∼ 5.2-5.7 (Ln = Gd, Dy, Ho) have been obtained for the first time by prolonged (40-160 h) heat treatment of mechanically activated 5Ln2O3 + 2MoO3 (Ln = Gd, Dy, Ho) oxide mixtures at 1200 °C. Although the starting Ln : Mo ratio was 5 : 1 (Ln10Mo2O21 (Ln = Dy, Ho)), it changed slightly in the final product due to the volatility of molybdenum oxide at 1200 °C (40-160 h) (ICP-MS analysis). Brief high-temperature firing (1600 °C, 3 h) of 5Ln2O3 + 2MoO3 (Ln = Gd, Dy, Ho) oxide mixtures leads to the formation of phase-pure fluorites with compositions close to Ln10Mo2O21 (Ln = Gd, Dy, Ho). Gd10Mo2O21 molybdate seems to undergo an order-disorder (orthorhombic-fluorite) phase transition in the range of 1200-1600 °C. For the first time, using the neutron diffraction method, it was shown that low-temperature phases with a Ln/Mo ratio ∼ 5.2-5.7 (Ln = Gd, Dy, Ho) have an orthorhombic structure rather than a tetragonal structure. Proton contribution to the total conductivity of Ln10Mo2O21 (Ln = Gd, Dy, Ho) fluorites and gadolinium and dysprosium orthorhombic phases in a wet atmosphere was observed for the first time. In both orthorhombic and fluorite phases, the total conductivity in wet air decreases with decreasing lanthanide ionic radii. In a wide temperature range, the compounds under study exhibit paramagnetic behaviour. However, the orthorhombic phases of Dy and Ho compounds reach the antiferromagnetic state at 2.4 K and 2.6 K, respectively.