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A potassium salt of the N2S2O2-coordination Fe(III) anion K[Fe(5Cl-thsa)2] (1) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K+ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K+ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57Fe Mossbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (ΔγHS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P21/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57Fe Mossbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.

A novel sodium bismuth oxo-cuprate phosphate chloride, Na6Cu7BiO4(PO4)4[Cl2.23(OH)0.77], containing square-kagome layers of Cu2+ has been synthesized by hydrothermal techniques. The compound crystallizes in the tetragonal space group P4/nmm, a = 10.0176(4), c = 10.8545(6), Z = 2, V = 1089.3(1) A3, R1 = 0.021, wR = 0.053, S = 1.32. Its composite crystal structure includes [O4Cu6Bi]7+ layers, which are formed by the clusters of oxygen-centered tetrahedra [OCu3Bi]. These positively charged two periodic fragments are intercalated in a negatively charged [CuNa6Cl3(PO4)4]7- matrix built by Na-centered polyhedra, PO4 tetrahedra, and CuO4Cl pyramids. The composite character of the crystal structure of Na6Cu7BiO4(PO4)4[Cl2.23(OH)0.77], as well as the way of its self-assembly, are discussed in close connection with the sulfohalite Na6ClF(SO4)2 salt. It is shown that the "host-guest" model of the formation of the tetragonal Na6Cu7BiO4(PO4)4[Cl2.23(OH)0.77] phase is due to the group-subgroup symmetry relation with the cubic crystal structure of mineral sulfohalite and is also supported by the crystallization condition in excess sodium chloride. The magnetic subsystem of Na6Cu7BiO4(PO4)4[Cl2.23(OH)0.77] is represented by a dense square-kagome network of 2Cu1 and 4Cu2 ions, decorated with weakly bonded Cu3 ions. Measurements of magnetization and heat capacity indicate the absence of long-range order up to 2 K, which makes this compound a candidate for a highly demanded spin liquid.

A novel modification of the KCoPO4, δ-phase has been prepared by hydrothermal synthesis at 553 K. The compound crystallizes in the orthorhombic system with the unit-cell parameters a = 8.5031(8), b = 10.2830(5), c = 54.170(4) A. The crystal structure was determined based on synchrotron low-temperature single-crystal X-ray diffraction data obtained from an inversion twin in the space group P212121 and refined to R = 0.077 for 5156 reflections with I > 3σ(I). The δ-KCoPO4 possesses a new structure type which is based on a framework built from sharing vertices Co- and P-centered tetrahedra. The {CoPO4-}∞ construction of tetrahedra may be described as assembled from networks formed by two topologically diverse six-membered rings of tetrahedra stacked together through vertex-bridging contacts along the a axis. The ratio of the (UUUDDD) and (UUDUDD) rings, where (U) and (D) denote the orientation of the tetrahedra in the six-membered rings up and down relative to the plane grids, is equal to 5:1. The (UUDUDD) rings form bands parallel to the [010] direction each surrounded from both sides along the c axis by slabs of five ribbons width having alternative (UUUDDD) topology. Open in the [100] direction channels incorporate K+ ions; this structural feature permits to suppose ion-conductive and/or electrochemical properties of the title compound. The possible mechanism of the δ → γ phase transition is discussed on the basis of the crystal chemical analysis of the KCoPO4 polymorphs. The title compound orders magnetically at TN = 24.8 K.

The unique family of coordination polymers [Ln4(OH)2(piv)10(H2O)2]∞ of 11 lanthanides (Ln = La-Er) has been prepared by a simple solution method based on controlled hydrolysis. The ribbon-like polymeric structure consisting of connected tetranuclear clusters and supported by pivalate ligands and a framework of H-bonds has been revealed by single-crystal X-ray diffraction. While the compounds demonstrate similar PXRD patterns and unit cell parameters, the joint single-crystal XRD and pair distribution function data suggest the significant local structure change along the lanthanide series. The compounds exist as two packing polymorphs (α and β) with similar ribbon geometry, but different supramolecular arrangement of the ribbons. Dehydration of either polymorph does not disturb the tetranuclear core but leads to a translational symmetry loss along the ribbon and a transformation of the 3D-ordered crystal into a 2D-ordered mesostructure. Rehydration of the mesostructure leads to the β polymorph (except La and Ce), allowing the deliberate switching between the polymorphs via dehydration-rehydration evidenced by means of powder X-ray diffraction, pair distribution function analysis, and density functional theory calculations. Ab initio calculations reveal significant magnetic anisotropy of Ln3+ ions with ferro- and antiferromagnetic interactions within tetranuclear [Ln4(OH)2(piv)10(H2O)2] species. Magnetic susceptibility measurements demonstrated antiferromagnetic coupling, slow magnetic relaxation for Dy, Ho, and Er complexes, and field-induced single-chain magnetism for the Dy compound.

A new hexacoordinate Co(II) complex with the general formula [CoL(NCS)2]·DMSO (1) (L = biscondensation product of diacetyl and 2-hydrazinyl-4,6-dimethylpyrimidine, DMSO = dimethylsulfoxide) exhibit...

Due to their physical properties and potential applications in energy conversion and storage, transition-metal dichalcogenides (TMDs) have garnered substantial interest in recent years. Among this class of materials, TMDs based on molybdenum, tungsten, sulfur, and selenium are particularly attractive due to their semiconducting properties and the availability of bottom-up synthesis techniques. Here we report a method which yields high-quality crystals of transition-metal diselenide and ditelluride compounds (PtTe2, PdTe2, NiTe2, TaTe2, TiTe2, RuTe2, PtSe2, PdSe2, NbSe2, TiSe2, VSe2, ReSe2) from their solid solutions, via vapor deposition from a metal-saturated chalcogen melt. Additionally, we show the synthesis of rare-earth-metal polychalcogenides and NbS2 crystals using the aforementioned process. Most of the crystals obtained have a layered CdI2 structure. We have investigated the physical properties of selected crystals and compared them to state of the art findings reported in the literature. Remarkably, the charge density wave transition in 1T-TiSe2 and 2H-NbSe2 crystals is well-defined at TCDW ≈ 200 and 33 K, respectively. Angle-resolved photoelectron spectroscopy and electron diffraction are used to directly access the electronic and crystal structures of PtTe2 single crystals and yield state of the art measurements. © 2020 American Chemical Society. M.A.-H. acknowledges support from the VR starting grant 2018-05339 and KL1824/6. The crystal growth experiments were supported by the Russian Science Foundation, Project 19-12-00414. The work has been supported by the program 211 of the Russian Federation Government agreements 02.A03.21.0006 and 02.A03.21.0011, by the Russian Government Program of Competitive Growth of Kazan Federal University. We acknowledge MAX IV Laboratory for time on Beamline Bloch under Proposal 20190335. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152 the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. We acknowledge ARPES experiment support from Craig Polley (MAX IV), Maciej Dendzik (KTH) Antonija Grubisic-Cabo (KTH) and Oscar Tjernberg (KTH). H.R., D.P. and G.J.M. acknowledge the Swedish Research Council (2018-06465, 2018-04330) and the Swedish Energy Agency (P43549-1) for financial support.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N3)C2H5OH]C2H5OH}n where H2DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N3O2] ligand and Ln = Dy (1), Y0.930Dy0.070 (2), Er (3), Y0.923Er0.077 (4), and Gd (5). X-ray diffraction analysis of 1-5 show that the central lanthanide atoms are eight-coordinated with the N5O3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N3- bridges connecting the metal centers into infinite chain. The [LnN5O3] coordination polyhedron can be regarded as a distorted dodecahedron (D2d). AC magnetic measurements revealed that compounds 1-4 show field-induced single-molecule magnet behavior, with estimated energy barriers Ueff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln3+ ions mediated by the end-to-end azide bridging groups (J ≈ -0.015 cm-1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln3+ ions.

The presence of both strong interchain and intrachain interactions of an antiferromagnetic as well as an ferromagnetic nature may lead to the appearance of a gap in the magnetic excitation spectrum of LiCu2(VO4)(OH)2 as evidenced by the hump in magnetic susceptibility χ at T* ≈ 30 K. The temperature range of short-range magnetic order is terminated by the onset of long-range magnetic order at TN = 10 K, which is triggered by substantial interchain exchange interactions. This observation is corroborated by the specific heat, Cp, singularity, electron spin resonance, and nuclear magnetic resonance measurements. The latter reveals a broad distribution of the resonance fields ascribed to the formation of a helix magnetic structure. First-principles calculations allow estimations of both intrachain and interchain exchange interaction parameters, suggesting the implementation of a strongly coupled scenario with competing inter- and intrachain interactions.

We report the first four magnetic representatives of the trigonal layered A2M(4+)TeO6 (here, M = Mn) family. Na2MnTeO6 was synthesized from NaMnO2, NaNO3, and TeO2 at 650–720 °C, but analogues for ...

We report the results of magnetization and specific heat measurements, a 57Fe Mossbauer study of hyperfine interactions and density functional theory calculations in TlFe(MoO4)2 demonstrating two m...

We report the first highly conducting single-molecule magnet, (BEDO)4[ReF6]·6H2O [1; BEDO = bis(ethylenedioxo)tetrathiafulvalene], whose conductivity and single-molecule magnetism coexist in the same temperature range. The compound was synthesized by BEDO electrocrystallization in the presence of (Ph4P)2[ReF6]·2H2O and characterized by crystallography and measurements of the conductivity and alternating-current magnetic susceptibility.

Four new manganese germanates and silicates, A2MnGeO4 (A = Li, Na) and A2MnSiO4 (A = Na, Ag), were prepared, and their crystal structures were determined using the X-ray Rietveld method. All of them contain all components in tetrahedral coordination. Li2MnGeO4 is orthorhombic (Pmn21) layered, isostructural with Li2CdGeO4, and the three other compounds are monoclinic (Pn) cristobalite-related frameworks. As in other stuffed cristobalites of various symmetry (Pn A2MXO4, Pna21 and Pbca AMO2), average bond angles on bridging oxygens (here, Mn–O–X) increase with increasing A/X and/or A/M radius ratios, indicating the trend to the ideal cubic (Fd3m) structure typified by CsAlO2. The sublattices of the magnetic Mn2+ ions in both structure types under study (Pmn21 and Pn) are essentially the same; namely, they are pseudocubic eutaxy with 12 nearest neighbors. The magnetic properties of the four new phases plus Li2MnSiO4 were characterized by carrying out magnetic susceptibility, specific heat, magnetization, and...

The manganese orthophosphate, Mn3(PO4)2, is characterized by the rich variety of polymorphous modifications, α-, β'-, and γ-phases, crystallized in monoclinic P21/c (P21/n) space group type with unit cell volume ratios of 2:6:1. The crystal structures of these phases are constituted by three-dimensional framework of corner- and edge-sharing [MnO5] and [MnO6] polyhedra strengthened by [PO4] tetrahedra. All compounds experience long-range antiferromagnetic order at Neel temperature TN = 21.9 K (α-phase), 12.3 K (β'-phase), and 13.3 K (γ-phase). Additionally, second magnetic phase transition takes place at T* = 10.3 K in β'-phase. The magnetization curves of α- and β'-modifications evidence spin-floplike features at B = 1.9 and 3.7 T, while the γ-Mn3(PO4)2 stands out for an extended one-third magnetization plateau stabilized in the range of magnetic field B = 7.5-23.5 T. The first-principles calculations define the main paths of superexchange interaction between Mn spins in these polymorphs. The spin model for α-phase is found to be characterized by collection of uniform and alternating chains, which are coupled in all three directions. The strongest magnetic exchange interaction in γ-phase emphasizes the trimer units, which make chains that are in turn weakly coupled to each other. The spin model of β'-phase turns out to be more complex compared to α- or γ-phase. It shows complex chain structures involving exchange interactions between Mn2 (Mn2', Mn2″) and Mn3 (Mn3', Mn3″). These chains interact through exchanges involving Mn1 (Mn1', Mn1″) spins.

We report the synthesis and characterization of the new bismuth iron selenite oxochloride Bi2Fe(SeO3)2OCl3. The main feature of its crystal structure is the presence of a reasonably isolated set of spin S = 5/2 zigzag chains of corner-sharing FeO6 octahedra decorated with BiO4Cl3, BiO3Cl3, and SeO3 groups. When the temperature is lowered, the magnetization passes through a broad maximum at Tmax ≈ 130 K, which indicates the formation of a magnetic short-range correlation regime. The same behavior is demonstrated by the integral electron spin resonance intensity. The absorption is characterized by the isotropic effective factor g ≈ 2 typical for high-spin Fe(3+) ions. The broadening of ESR absorption lines at low temperatures with the critical exponent β = 7/4 is consistent with the divergence of the temperature-dependent correlation length expected for the quasi-one-dimensional antiferromagnetic spin chain upon approaching the long-range ordering transition from above. At TN = 13 K, Bi2Fe(SeO3)2OCl3 exhibits a transition into an antiferromagnetically ordered state, evidenced in the magnetization, specific heat, and Mössbauer spectra. At TTN, the (57)Fe Mössbauer spectra reveal a low saturated value of the hyperfine field Hhf ≈ 44 T, which indicates a quantum spin reduction of spin-only magnetic moment ΔS/S ≈ 20%. The determination of exchange interaction parameters using first-principles calculations validates the quasi-one-dimensional nature of magnetism in this compound.

A new orthorhombic phase, MnCrO4, isostructural with MCrO 4 (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH4)2Cr2O7 + 2 Mn(NO 3)2, followed by calcination at 400 C. It is characterized by redox titration, Rietveld analysis of the X-ray diffraction pattern, Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific heat and resistivity measurements. In contrast to the high-pressure MnCrO4 phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn2+Cr 6+O4. However, the positions of both X-ray absorption K edges, the bond lengths and the ESR data suggest the occurrence of some mixed-valence character in which the mean oxidation state of Mn is higher than 2 and that of Cr is lower than 6. Both the magnetic susceptibility and the specific heat data indicate an onset of a three-dimensional antiferromagnetic order at TN ≈ 42 K, which was confirmed also by calculating the spin exchange interactions on the basis of first principles density functional calculations. Dynamic magnetic studies (ESR) corroborate this scenario and indicate appreciable short-range correlations at temperatures far above T N. MnCrO4 is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 C to form first Cr 2O3 plus Mn3O4 and then Mn 1.5Cr1.5O4 spinel. © 2013 American Chemical Society.

Large and high quality single crystals of the new unconventional superconductor LiFeAs were grown by a new approach using the self-flux technique. Both energy dispersive X-ray spectroscopy and inductively coupled plasma mass spectroscopy revealed a stoichiometric Li/Fe/As composition. Measurements of the magnetic susceptibility reveal the superconducting transition at TC = 17 K with a very sharp ΔTC and a 100% shielding fraction and, thus, bulk superconductivity. This sharp transition is also found by measurements of the specific heat and by measurements of the temperature dependence of the resistivity. Nuclear quadrupole resonance (NQR) spectroscopy reveals a very sharp resonance line, with a much smaller line width than reported for all other FeAs superconductors, confirming the high ordering of the LiFeAs single crystals also on a local scale.

A new type of composite structure is described consisting of the todorokite-type [Mn 6 O 12 ] framework with large square tunnels accommodating columnar fragments of the rock-salt structure. The crystal structure of the new todorokite-type [SrF 0.8 (OH) 0.2 ] 2.526 [Mn 6 O 12 ] compound is solved from transmission electron microscopy, and the structure of its anhydrous form [SrF 0.8 O 0.1 ] 2.526 [Mn 6 O 12 ] is refined from X-ray powder diffraction data. The [Mn 6 O 12 ] framework consists of mutually perpendicular walls built of three edge-sharing rutile-type strings of MnO 6 octahedra delimiting large square tunnels with the size of 3 x 3 octahedra. The interior space in the tunnels is filled with rock-salt type [Sr(F,OH)] 4 columns. The structure can be interpreted as being an incommensurate composite structure with the modulation vector q 1 = γc 1 * (y = 0.63157(3)) parallel to the direction of tunnel propagation. The octahedral tunnel walls compose subsystem I with a [Mn 6 Ο 12 ] composition and a periodicity c 1 = 2.84 A, whereas the [Sr(F,OH)] 4 columns belong to subsystem II with a periodicity c 1 /γ = 4.49 A, resulting in a [Sr(F,-OH)] 4γ [Mn 6 O 12 ] composition. [SrF 0.8 (OH) 0.2 ] 2.526 [Mn 6 O 12 ] demonstrates a much larger number of cations inside the tunnels in comparison with the known synthetic and natural marine todorokites. The [SrF 0.8 -(OH) 0.2 ] 2.526 [Mn 6 O 12 ] compound shows a spin-glass behavior below T* ≈ 26 K with a dominant antiferromagnetic correlation.