Synthesis and in-depth structure determination of a novel metastable high-pressure CrTe3 phase.

This study reports the synthesis and crystal structure determination of a novel CrTe3 phase using various experimental and theoretical methods. The average stoichiometry and local phase separation of this quenched high-pressure phase were characterized by ex situ synchrotron powder X-ray diffraction and total scattering. Several structural models were obtained using simulated annealing, but all suffered from an imperfect Rietveld refinement, especially at higher diffraction angles. Finally, a novel stoichiometrically correct crystal structure model was proposed on the basis of electron diffraction data and refined against powder diffraction data using the Rietveld method. Scanning electron microscopy-energy-dispersive X-ray spectrometry (EDX) measurements verified the targeted 1:3 (Cr:Te) average stoichiometry for the starting compound and for the quenched high-pressure phase within experimental errors. Scanning transmission electron microscopy (STEM)-EDX was used to examine minute variations of the Cr-to-Te ratio at the nanoscale. Precession electron diffraction (PED) experiments were applied for the nanoscale structure analysis of the quenched high-pressure phase. The proposed monoclinic model from PED experiments provided an improved fit to the X-ray patterns, especially after introducing atomic anisotropic displacement parameters and partial occupancy of Cr atoms. Atomic resolution STEM and simulations were conducted to identify variations in the Cr-atom site-occupancy factor. No significant variations were observed experimentally for several zone axes. The magnetic properties of the novel CrTe3 phase were investigated through temperature- and field-dependent magnetization measurements. In order to understand these properties, auxiliary theoretical investigations have been performed by first-principles electronic structure calculations and Monte Carlo simulations. The obtained results allow the observed magnetization behavior to be interpreted as the consequence of competition between the applied magnetic field and the Cr-Cr exchange interactions, leading to a decrease of the magnetization towards T = 0 K typical for antiferromagnetic systems, as well as a field-induced enhanced magnetization around the critical temperature due to the high magnetic susceptibility in this region.

Sonication-assisted liquid phase exfoliation of two-dimensional CrTe3 under inert conditions.

Liquid phase exfoliation (LPE) has been used for the successful fabrication of nanosheets from a large number of van der Waals materials. While this allows to study fundamental changes of material properties' associated with reduced dimensions, it also changes the chemistry of many materials due to a significant increase of the effective surface area, often accompanied with enhanced reactivity and accelerated oxidation. To prevent material decomposition, LPE and processing in inert atmosphere have been developed, which enables the preparation of pristine nanomaterials, and to systematically study compositional changes over time for different storage conditions. Here, we demonstrate the inert exfoliation of the oxidation-sensitive van der Waals crystal, CrTe3. The pristine nanomaterial was purified and size-selected by centrifugation, nanosheet dimensions in the fractions quantified by atomic force microscopy and studied by Raman, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and photo spectroscopic measurements. We find a dependence of the relative intensities of the CrTe3 Raman modes on the propagation direction of the incident light, which prevents a correlation of the Raman spectral profile to the nanosheet dimensions. XPS and EDX reveal that the contribution of surface oxides to the spectra is reduced after exfoliation compared to the bulk material. Further, the decomposition mechanism of the nanosheets was studied by time-dependent extinction measurements after water titration experiments to initially dry solvents, which suggest that water plays a significant role in the material decomposition.

Room-Temperature Solid-State Transformation of Na4 SnS4 ⋠14H2 O into Na4 Sn2 S6 ⋠5H2 O: An Unusual Epitaxial Reaction Including Bond Formation, Mass Transport, and Ionic Conductivity.

A highly unusual solid-state epitaxy-induced phase transformation of Na4 SnS4 ⋅ 14H2 O (I) into Na4 Sn2 S6 ⋅ 5H2 O (II) occurs at room temperature. Ab initio molecular dynamics (AIMD) simulations indicate an internal acid-base reaction to form [SnS3 SH]3- which condensates to [Sn2 S6 ]4- . The reaction involves a complex sequence of O-H bond cleavage, S2- protonation, Sn-S bond formation and diffusion of various species while preserving the crystal morphology. In situ Raman and IR spectroscopy evidence the formation of [Sn2 S6 ]4- . DFT calculations allowed assignment of all bands appearing during the transformation. X-ray diffraction and in situ 1 H NMR demonstrate a transformation within several days and yield a reaction turnover of ≈0.38 %/h. AIMD and experimental ionic conductivity data closely follow a Vogel-Fulcher-Tammann type T dependence with D(Na)=6×10-14  m2 s-1 at T=300 K with values increasing by three orders of magnitude from -20 to +25 °C.

Composition-driven archetype dynamics in polyoxovanadates.

Molecular metal oxides often adopt common structural frameworks (i.e. archetypes), many of them boasting impressive structural robustness and stability. However, the ability to adapt and to undergo transformations between different structural archetypes is a desirable material design feature offering applicability in different environments. Using systems thinking approach that integrates synthetic, analytical and computational techniques, we explore the transformations governing the chemistry of polyoxovanadates (POVs) constructed of arsenate and vanadate building units. The water-soluble salt of the low nuclearity polyanion [V6As8O26]4- can be effectively used for the synthesis of the larger spherical (i.e. kegginoidal) mixed-valent [V12As8O40]4- precipitate, while the novel [V10As12O40]8- POVs having tubular cyclic structures are another, well soluble product. Surprisingly, in contrast to the common observation that high-nuclearity polyoxometalate (POM) clusters are fragmented to form smaller moieties in solution, the low nuclearity [V6As8O26]4- anion is in situ transformed into the higher nuclearity cluster anions. The obtained products support a conceptually new model that is outlined in this article and that describes a continuous evolution between spherical and cyclic POV assemblies. This new model represents a milestone on the way to rational and designable POV self-assemblies.

Directed Dehydration as Synthetic Tool for Generation of a New Na4 SnS4 Polymorph: Crystal Structure, Na+ Conductivity, and Influence of Sb-Substitution.

We present the convenient synthesis and characterization of the new ternary thiostannate Na4 SnS4 (space group I 4 1 / a c d ) by directed removal of crystal water molecules from Na4 SnS4 ⋅14 H2 O. The compound represents a new kinetically stable polymorph of Na4 SnS4 , which is transformed into the known, thermodynamically stable form (space group P 4 ‾ 2 1 c ) at elevated temperatures. Thermal co-decomposition of mixtures with Na3 SbS4 ⋅9 H2 O generates solid solution products Na4-x Sn1-x Sbx S4 (x=0.01, 0.10) isostructural to the new polymorph (x=0). Incorporation of Sb5+ affects the bonding and local structural situation noticeably evidenced by X-ray diffraction, 119 Sn and 23 Na NMR, and 119 Sn Mössbauer spectroscopy. Electrochemical impedance spectroscopy demonstrates an enormous improvement of the ionic conductivity with increasing Sb content for the solid solution (σ25°C =2×10-3 , 2×10-2 , and 0.1 mS cm-1 for x=0, 0.01, and 0.10), being several orders of magnitude higher than for the known Na4 SnS4 polymorph.

Crystal structure of µ3-tetra-thio-anti-monato-tris[(cyclam)zinc(II)] tetra-thio-anti-monate aceto-nitrile disolvate dihydrate showing Zn disorder over the cyclam ring planes (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne).

Reaction of Zn(ClO4)2·6H2O with cyclam (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4) and Na3SbS4 in an aceto-nitrile/water mixture led to the formation of crystals of the title compound, [Zn3(SbS4)(C10H24N4)3](SbS4)·2CH3CN·2H2O or [(Zn-cyclam)3(SbS4)2](H2O)2(aceto-nitrile)2. The set-up of the crystal structure is similar to that of [(Zn-cyclam)3(SbS4)2].8H2O reported recently [Danker et al. (2021 ▸). Dalton Trans. 50, 18107-18117]. The crystal structure of the title compound consists of three crystallographically independent ZnII cations (each disordered around centers of inversion), three centrosymmetric cyclam ligands, one SbS4 3- anion, one water and one aceto-nitrile mol-ecule occupying general positions. The aceto-nitrile mol-ecule is equally disordered over two sets of sites. Each Zn2+ cation is bound to four nitro-gen atoms of a cyclam ligand and one sulfur atom of the SbS4 3- anion within a distorted square-pyramidal coordination. The cation disorder of the [Zn(cyclam)]2+ complexes is discussed in detail and is also observed in other compounds, where identical ligands are located above and below the [Zn(cyclam)]2+ plane. In the title compound, the building units are arranged in layers parallel to the bc plane forming pores in which the aceto-nitrile solvate mol-ecules are located. Inter-molecular C-H⋯S hydrogen bonding links these units to the SbS4 3- anions. Between the layers, additional water solvate mol-ecules are present that act as acceptor and donor groups for inter-molecular N-H⋯O and O-H⋯S hydrogen bonding.

Synthesis and crystal structure of poly[[di-µ3-tetra-thio-anti-monato-tris-[(cyclam)cobalt(II)]] aceto-nitrile disolvate dihydrate] (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne).

Reaction of Co(ClO4)2·6H2O with cyclam (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne) and Na3SbS4·9H2O (Schlippesches salt) in a mixture of aceto-nitrile and water leads to the formation of crystals of the title compound with the composition {[Co3(SbS4)2(C10H24N4)3]·2CH3CN·2H2O} n or {[(Co-cyclam)3(SbS4)2]·2(aceto-nitrile)·2H2O} n . The crystal structure of the title compound consists of three crystallographically independent [Co-cyclam]2+ cations, which are located on centers of inversion, one [SbS4]3- anion, one water and one aceto-nitrile mol-ecule that occupy general positions. The aceto-nitrile mol-ecule is disordered over two orientations and was refined using a split model. The CoII cations are coordinated by four N atoms of the cyclam ligand and two trans-S atoms of the tetra-thio-anti-monate anion within slightly distorted octa-hedra. The unique [SbS4]3- anion is coordinated to all three crystallographically independent CoII cations and this unit, with its symmetry-related counterparts, forms rings composed of six Co-cyclam cations and six tetra-thio-anti-monate anions that are further condensed into layers. These layers are perfectly stacked onto each other so that channels are formed in which acetontrile solvate mol-ecules that are hydrogen bonded to the anions are embedded. The water solvate mol-ecules are located between the layers and are connected to the cyclam ligands and the [SbS4]3- anions via inter-molecular N-H⋯O and O-H⋯S hydrogen bonding.

Time-dependent investigation of a mechanochemical synthesis of bismuth telluride-based materials and their structural and thermoelectric properties.

Here, we report on the time dependence of a synthesis procedure for generation of both n- and p-type bismuth telluride-based materials. To initiate the reaction, the starting materials were first mechanical pre-reacted. The Rietveld refinements of X-ray diffraction (XRD) data collected after different milling times demonstrate that Bi2Te3 was formed after only 10 min, and longer milling times do not alter the composition. To complete the phase formation, the powders were treated by field-assisted sintering and heat treatment afterwards. The effect of this fast procedure on the structural and thermoelectric properties was investigated. Samples were obtained with relative densities above 99%. A clear preferred orientation of the crystallites in the samples is evidenced by Rietveld refinements of XRD data. The thermoelectric characteristics demonstrate a good performance despite the short milling time. Further, it was demonstrated for this fast synthesis that the physical transport properties can be varied with well-known n- and p-type dopants like CHI3 or Pb. For these non-optimized materials, a ZT value of 0.7 (n-type) and 0.9 (p-type) between 400 and 450 K was achieved. The long-term stability is demonstrated by repeated measurements up to 523 K showing no significant alteration of the thermoelectric performance.

Understanding sodium storage properties of ultra-small Fe3S4 nanoparticles - a combined XRD, PDF, XAS and electrokinetic study.

Various electrode materials are considered for sodium-ion batteries (SIBs) and one important prerequisite for developments of SIBs is a detailed understanding about charge storage mechanisms. Herein, we present a rigorous study about Na storage properties of ultra-small Fe3S4 nanoparticles, synthesized applying a solvothermal route, which exhibit a very good electrochemical performance as anode material for SIBs. A closer look into electrochemical reaction pathways on the nanoscale, utilizing synchrotron-based X-ray diffraction and X-ray absorption techniques, reveals a complicated conversion mechanism. Initially, separation of Fe3S4 into nanocrystalline intermediates occurs accompanied by reduction of Fe3+ to Fe2+ cations. Discharge to 0.1 V leads to formation of strongly disordered Fe0 finely dispersed in a nanosized Na2S matrix. The resulting volume expansion leads to a worse long-term stability in the voltage range 3.0-0.1 V. Adjusting the lower cut-off potential to 0.5 V, crystallization of Na2S is prevented and a completely amorphous intermediate stage is formed. Thus, the smaller voltage window is favorable for long-term stability, yielding highly reversible capacity retention, e.g., 486 mAh g-1 after 300 cycles applying 0.5 A g-1 and superior coulombic efficiencies >99.9%. During charge to 3.0 V, Fe3S4 with smaller domains are reversibly generated in the 1st cycle, but further cycling results in loss of structural long-range order, whereas the local environment resembles that of Fe3S4 in subsequent charged states. Electrokinetic analyses reveal high capacitive contributions to the charge storage, indicating shortened diffusion lengths and thus, redox reactions occur predominantly at surfaces of nanosized conversion products.

The cation and anion bonding modes make a difference: an unprecedented layered structure and a tri(hetero)nuclear moiety in thioantimonates(V).

Mixing solutions of M2+ (M = Cu2+ or Zn2+) salts containing cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) as the ligand and an aqueous solution of Na3SbS4·9H2O at room temperature led to the crystallization of two new compounds within minutes: {[Cu(cyclam)]3[SbS4]2}n·20nH2O (I) and {[Zn(cyclam)]3[SbS4]2}·8H2O (II). In the structure of I [SbS4]3- anions acting as a tridentate ligand join CuN4S2 octahedra generating twelve-membered rings by corner-sharing of SbS4 and CuN4S2 units. The rings are condensed into layers, which are stacked onto each other in a 6R polytype manner. The layers contain large pores with the water molecules located between the layers above and below the pores. In contrast, the structure of II comprises a discrete molecular tri(hetero)nuclear moiety with a bidentate [SbS4]3- anion connecting two rectangular pyramidal ZnN4S polyhedra. The crystal water molecules of I and II can be thermally removed, and I and II are recovered by treatment under a humid atmosphere. The EPR spectrum of I indicates the presence of Cu2+ cations, which is unusual in the environment of S2- anions. The different bonding situations and the preferences for the coordination geometries of Cu2+ and Zn2+ cations are rationalized by DFT based calculations, demonstrating that Cu2+ prefers an octahedral environment while Zn2+ adopts the square-pyramidal coordination. The pronounced differences in the vibrational spectra are also analyzed with DFT, showing how the different modes are influenced by the differing bond strengths.

Synthesis and crystal structure of bis-[µ-N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-bis-[N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-µ4-oxido-hexa-µ3-oxido-octa-µ2-oxido-tetra-oxido-tetra-nickel(II)hexa-tantalum(V) nona-deca-hydrate.

Reaction of K8{Ta6O19}·16H2O with [Ni(tren)(H2O)Cl]Cl·H2O in different solvents led to the formation of single crystals of the title compound, [Ni4Ta6O19(C6H18N4)4]·19H2O or {[Ni2(κ4-tren)(µ-κ3-tren)]2Ta6O19}·19H2O (tren is N,N-bis-(2-amino-eth-yl)-1,2-ethanediamine, C6H18N4). In its crystal structure, one Lindqvist-type anion {Ta6O19}8- (point group symmetry ) is connected to two NiII cations, with both of them coordinated by one tren ligand into discrete units. Both NiII cations are sixfold coordinated by O atoms of the anion and N atoms of the organic ligand, resulting in slightly distorted [NiON5] octa-hedra for one and [NiO3N3] octa-hedra for the other cation. These clusters are linked by inter-molecular O-H⋯O and N-H⋯O hydrogen bonding involving water mol-ecules into layers parallel to the bc plane. Some of these water mol-ecules are positionally disordered and were refined using a split model. Powder X-ray diffraction revealed that a pure crystalline phase was obtained but that on storage at room-temperature this compound decomposed because of the loss of crystal water mol-ecules.

Synthetically Produced Isocubanite as an Anode Material for Sodium-Ion Batteries: Understanding the Reaction Mechanism During Sodium Uptake and Release.

Bulk isocubanite (CuFe2S3) was synthesized via a multistep high-temperature synthesis and was investigated as an anode material for sodium-ion batteries. CuFe2S3 exhibits an excellent electrochemical performance with a capacity retention of 422 mA h g-1 for more than 1000 cycles at a current rate of 0.5 A g-1 (0.85 C). The complex reaction mechanism of the first cycle was investigated via PXRD and X-ray absorption spectroscopy. At the early stages of Na uptake, CuFe2S3 is converted to form crystalline CuFeS2 and nanocrystalline NaFe1.5S2 simultaneously. By increasing the Na content, Cu+ is reduced to nanocrystalline Cu, followed by the reduction of Fe2+ to amorphous Fe0 while reflections of nanocrystalline Na2S appear. During charging up to -5 Na/f.u., the intermediate NaFe1.5S2 appears again, which transforms in the last step of charging to a new unknown phase. This unknown phase together with NaFe1.5S2 plays a key role in the mechanism for the following cycles, evidenced by the PXRD investigation of the second cycle. Even after 400 cycles, the occurrence of nanocrystalline phases made it possible to gain insights into the alteration of the mechanism, which shows that CuxS phases play an important role in the region of constant specific capacity.

Long-Term Stable, High-Capacity Anode Material for Sodium-Ion Batteries: Taking a Closer Look at CrPS4 from an Electrochemical and Mechanistic Point of View.

Electrochemical performance of the layered compound CrPS4 for the usage as anode material in sodium-ion batteries (SIBs) was examined and exceptional reversible long-term capacity and capacity retention were found. After 300 cycles, an extraordinary reversible capacity of 687 mAh g-1 at a current rate of 1 A g-1 was achieved, while rate capability tests showed an excellent capacity retention of 100%. Detailed evaluation of the data evidence a change of the electrochemical reaction upon cycling leading to the striking long-term performance. Further investigations targeted the reaction mechanism of the first cycle by applying complementary techniques, i.e., powder X-ray diffraction (XRD), pair distribution function (PDF) analysis, X-ray absorption spectroscopy (XAS), and 23Na/31P magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The results indicated an unexpectedly complex reaction pathway including formation of several intercalation compounds, depending on the amount of Na inserted at the early discharge states and subsequent conversion to Na2S and strongly disordered metallic Cr at the completely discharged state. While XAS measurements suggest no further presence of intermediates after formation of Na intercalation compounds, several different phases are detected via MAS NMR upon continued discharging. Especially the data obtained from the MAS NMR investigations therefore point toward a very complex reaction pathway. Furthermore, solid electrolyte interphase (SEI) formation, resulting in the presence of NaF, was observed. After recharging the anode material, no structural long-range order occurred, but short-range order indeed resembled the local environment of the starting material, to a certain extent.

Superior Sodium Storage Properties in the Anode Material NiCr2 S4 for Sodium-Ion Batteries: An X-ray Diffraction, Pair Distribution Function, and X-ray Absorption Study Reveals a Conversion Mechanism via Nickel Extrusion.

The pseudo-layered sulfide NiCr2 S4 exhibits outstanding electrochemical performance as anode material in sodium-ion batteries (SIBs). The Na storage mechanism is investigated by synchrotron-based X-ray scattering and absorption techniques as well as by electrochemical measurements. A very high reversible capacity in the 500th cycle of 489 mAh g-1 is observed at 2.0 A g-1 in the potential window 3.0-0.1 V. Full discharge includes irreversible generation of Ni0 and Cr0 nanoparticles embedded in nanocrystalline Na2 S yielding shortened diffusion lengths and predominantly surface-controlled charge storage. During charge, Ni0 and Cr0 are oxidized, Na2 S is consumed, and amorphous Ni and Cr sulfides are formed. Limiting the potential window to 3.0-0.3 V an unusual nickel extrusion sodium insertion mechanism occurs: Ni2+ is reduced to nanosized Ni0 domains, expelled from the host lattice, and is replaced by Na+ cations to form O3-type like NaCrS2 . Surprisingly, the discharge and charge processes comprise Na+ shuttling between highly crystalline NiCr2 S4 and NaCrS2 enabling a superior long-term stability for 3000 cycles. The results not only provide valuable insights for the electrochemistry of conversion materials but also extend the scope of layered electrode materials considering the reversible nickel extrusion sodium insertion reaction as new concept for SIBs.

Three intersecting {V12} rings: {V30Sb8}, an ultra-large polyoxovanadate cluster shell.

[VIV30SbIII8O78]12-, currently the largest known antimonato-polyoxovanadate (Sb-POV), features three perpendicular, intersecting 12-membered rings of edge-sharing O4V[double bond, length as m-dash]O square pyramids. While in two rings the apices of all O4V[double bond, length as m-dash]O pyramids point outwards, four apices of the third ring are directed into the cavity of the cluster shell, a concave structural motif not previously observed in polyoxovanadate chemistry. SbIII centers cap the eight niches defined by the octands of the {V30O78} cluster shell, resulting in discrete trigonal pyramidal SbO3 units, a second unprecedented feature. Within the resulting spin topology with numerous local geometrically frustrated motifs, the 30 spin-1/2 sites couple antiferromagnetically via a complex set of exchange pathways.

Mechanochemical Synthesis and Magnetic Characterization of Nanosized Cubic Spinel FeCr2S4 Particles.

Nanosized samples of the cubic thiospinel FeCr2S4 were synthesized by ball milling of FeS and Cr2S3 precursors followed by a distinct temperature treatment between 500 and 800 °C. Depending on the applied temperature, volume weighted mean (L vol) particle sizes of 56 nm (500 °C), 86 nm (600 °C), and 123 nm (800 °C) were obtained. All samples show a transition into the ferrimagnetic state at a Curie temperature T C of ∼ 167 K only slightly depending on the annealing temperature. Above T C, ferromagnetic spin clusters survive and Curie-Weiss behavior is observed only at T ≫ T C, with T depending on the heat treatments and the external magnetic field applied. Zero-field-cooled and field-cooled magnetic susceptibilities diverge significantly below T C in contrast to what is observed for conventionally solid-state-prepared polycrystalline samples. In the low-temperature region, all samples show a transition into the orbital ordered state at about 9 K, which is more pronounced for the samples heated to higher temperatures. This observation is a clear indication that the cation disorder is very low because a pronounced disorder would suppress this magnetic transition. The unusual magnetic properties of the samples at low temperatures and different external magnetic fields can be clearly related to different factors like structural microstrain and magnetocrystalline anisotropy.

CuFeS2 as a Very Stable High-Capacity Anode Material for Sodium-Ion Batteries: A Multimethod Approach for Elucidation of the Complex Reaction Mechanisms during Discharge and Charge Processes.

Highly crystalline CuFeS2 containing earth-abundant and environmentally friendly elements prepared via a high-temperature synthesis exhibits an excellent electrochemical performance as an anode material in sodium-ion batteries. The initial specific capacity of 460 mAh g-1 increases to 512 mAh g-1 in the 150th cycle and then decreases to a still very high value of 444 mAh g-1 at 0.5 A g-1 in the remaining 550 cycles. Even for a large current density, a pronounced cycling stability is observed. Here, we demonstrate that combining the results of X-ray powder diffraction experiments, pair distribution function analysis, and 23Na NMR and Mössbauer spectroscopy investigations performed at different stages of discharging and charging processes allows elucidation of very complex reaction mechanisms. In the first step after uptake of 1 Na/CuFeS2, nanocrystalline NaCuFeS2 is formed as an intermediate phase, which surprisingly could be recovered during charging. On increasing the Na content, Cu+ is reduced to nanocrystalline Cu, while nanocrystalline Na2S and nanosized elemental Fe are formed in the discharged state. After charging, the main crystalline phase is NaCuFeS2. At the 150th cycle, the mechanisms clearly changed, and in the charged state, nanocrystalline CuxS phases are observed. At later stages of cycling, the mechanisms are altered again: NaF, Cu2S, and Cu7.2S4 appeared in the discharged state, while NaF and Cu5FeS4 are observed in the charged state. In contrast to a typical conversion reaction, nanocrystalline phases play the dominant role, which are responsible for the high reversible capacity and long-term stability.

Synthesis and crystal structure of (1,4,7,10-tetra-aza-cyclo-dodecane-κ4 N)(tetra-sulfido-κ2 S 1,S 4)manganese(II).

The title compound, [Mn(S4)(C8H20N4)], was accidentally obtained by the hydro-thermal reaction of Mn(ClO4)2·6H2O, cyclen (cyclen = 1,4,7,10-tetra-aza-cyclo-dodeca-ne) and Na3SbS4·9H2O in water at 413 K, indicating that polysulfide anions might represent inter-mediates in the synthesis of thio-metallate compounds using Na3SbS4·9H2O as a reactant. X-ray powder diffraction proves that the sample is slightly contaminated with NaSb(OH)6 and an unknown crystalline phase. The crystal investigated was twinned with a twofold rotation axis as the twin element, and therefore a twin refinement using data in HKLF-5 format was performed. The asymmetric unit of the title compound consists of one MnII cation, one [S4]2- anion and one cyclen ligand in general positions. The MnII cation is sixfold coordinated by two cis-S atoms of the [S4]2- anions, as well as four N atoms of the cyclen ligand within an irregular coordination. The complexes are linked via pairs of N-H⋯S hydrogen bonds into chains, which are further linked into layers by additional N-H⋯S hydrogen bonding. These layers are connected into a three-dimensional network by inter-molecular N-H⋯S and C-H⋯S hydrogen bonding. It is noted that only one similar complex with MnII is reported in the literature.

Synthesis and crystal structure of catena-poly[[bis[(2,2';6',2''-terpyridine)-manganese(II)]-µ4-penta-thio-dianti-monato] tetra-hydrate] showing a 1D MnSbS network.

The asymmetric unit of the title compound, {[Mn2Sb2S5(C15H11N3)2]·4H2O} n , consists of two crystallographically independent MnII ions, two unique terpyridine ligands, one [Sb2S5]4- anion and four solvent water mol-ecules, all of which are located in general positions. The [Sb2S5]4- anion consists of two SbS3 units that share common corners. Each of the MnII ions is fivefold coordinated by two symmetry-related S atoms of [Sb2S5]4- anions and three N atoms of a terpyridine ligand within an irregular coordination. Each two anions are linked by two [Mn(terpyridine)]2+ cations into chains along the c-axis direction that consist of eight-membered Mn2Sb2S4 rings. These chains are further connected into a three-dimensional network by inter-molecular O-H⋯O and O-H⋯S hydrogen bonds. The crystal investigated was twinned and therefore, a twin refinement using data in HKLF-5 [Sheldrick (2015 ▸). Acta Cryst. C71, 3-8] format was performed.

HfTe2: Enhancing Magnetoresistance Properties by Improvement of the Crystal Growth Method.

We present a systematic study on the magnetotransport properties of HfTe2 single crystals grown by different synthetic protocols. Both chemical vapor transport (CVT) as well as the self-flux method were applied. Depending on the synthetic procedure the crystal quality is reflected by the residual resistivity ratio (RRR). The best CVT grown crystal shows a RRR of 262, while the crystal with the highest quality obtained with the Te self-flux method exhibits a value of 404. The superiority of the self-flux method can be traced back to its ability to reduce the amount of Zr as main contaminant more effectively compared to chemical vapor transport. The large RRR value is reflected in the magnetoresistance (MR) effect which reaches more than 9400%, outperforming the data published for HfTe2. The benefit of the self-flux approach was tested for WTe2 and a RRR of 2525 was reached significantly surpassing the data reported in literature. Crystals of both high and low RRR were compared with respect to the magnetotransport properties, i.e., transverse magnetoresistance and the Hall effect. The major factor determining the maximum value of the MR is the carrier mobility which is severely affected by the preparation conditions, while the carrier balance remains virtually unaffected.