Trigonal Prismatic Coordination Research Articles

Influence of Lithium Intercalation on Magnetic Properties of MoS2 Nanosheets

MoS2 is a member of a large class of 2-dimensional transition metal dichalcogenides (TMDs) with general formula MX2 (M-transition metal, X-chalcogen atom). In these 2D materials X-M-X monolayer comprises of M-layer sandwiched between two X-layers. Monolayers are held by weak van der Waals interaction in bulk compounds. Among various TMDs reported MoS2 has received great attention due to its exclusive properties like large spin-orbit coupling, layer dependent bandgap (1.2 eV to 1.8 eV) and high on/off current ratio making it a promising candidate for spintronics devices.1 Bulk MoS2 is diamagnetic in nature, hence it is necessary to tune its ferromagnetic properties to make it a potential candidate for spintronics applications. Several experiments like transition metal doping, inducing defects in MoS2 and structural phase transition have been shown to influence the ferromagnetic properties.MoS2 exists in different polymorphs, namely 1T, 2H and 3R. Mo in 2H and 3R phase resides in trigonal prismatic geometry. In this coordination electrons in d-orbital pair up oppositely resulting in a net zero magnetic moment. Whereas, in 1T phase Mo residing in octahedral geometry stabilizes in spin-polarized state giving net magnetic moment of 2μB per MoS2. This provides a pathway for enabling MoS2 ferromagnetic through structural phase transition (i.e. 3R/2H to 1T). Intercalating ions within the interlayer sites between adjacent MoS2 layers which takes place with an associated charge transfer to molybdenum enable such structural phase transition. This process leads to the trigonal prismatic (2H/3R) coordination of molybdenum unstable. Hence the system stabilizes in octahedral geometry (1T) via intralayer atomic plane gliding through transverse S-layer displacement. In this work, we utilize MoS2 nanosheets synthesized from wet chemical method to investigate the magnetic properties of Li+ intercalated MoS2 nanosheets. MoS2 nanosheets with different degrees of disorder can be obtained by controlling the annealing temperature.2 Planar and edge defect-rich MoS2 (MS-DR) are obtained upon annealing at 500 °C and defect-suppressed ordered layers of MoS2 nanosheets (MS-DS) are obtained upon annealing at 900 °C for 1 h. The former shows larger magnetization (0.10 emu/g) compared to the latter (0.03 emu/g). After lithium intercalation these MoS2 nanosheets show enhanced magnetization, 0.37 emu/g (for MS-DR) and 0.22 emu/g (MS-DS). Since the deintercalation process retains Li within the nanosheets based on the extent of defects present in MoS2, these nanosheets retain ferromagnetism even after deintercalation process. This presentation will discuss in detail the ferromagnetic properties of MoS2 nanosheets upon Li intercalation/deintercalation process.

YIrIn with ZrNiAl-type structure

Abstract The indide YIrIn was synthesized from the elements in a sealed tantalum ampoule in a high-frequency furnace. YIrIn adopts the ZrNiAl type. The crystal structure was refined from single-crystal X-ray diffractometer data: P6–2m, a = 750.63(6), c = 392.04(3) pm, wR = 0.0346, 308 F 2 values and 16 variables. Refinement of the occupancy parameters revealed a small degree of Ir/In mixing (0.912(9) Ir2/0.088(9) In1) on the 2d site. The YIrIn structure contains two crystallographically independent iridium sites, both with tri-capped trigonal prismatic coordination: Ir1@In6Y3 and Ir2@In3Y6.

Layering the charge

Batteries Layered metal oxides such as lithium cobalt oxide have attracted great attention for rechargeable batteries. In lithium cells, only the octahedral structure forms, but in sodium cells, trigonal prismatic structures are also possible. However, there is a lack of understanding about how to predict and control the formation of each structure. Zhao et al. used the simple properties of ions, namely their charge and their radius appropriately weighted by stoichiometry, to determine whether sodium in the interlayers between the transition metal or other ion-oxide layers remain octahedral rather than switching over to trigonal prismatic coordination. Science , this issue p. [708][1] [1]: /lookup/doi/10.1126/science.aay9972

Rational design of layered oxide materials for sodium-ion batteries.

Sodium-ion batteries have captured widespread attention for grid-scale energy storage owing to the natural abundance of sodium. The performance of such batteries is limited by available electrode materials, especially for sodium-ion layered oxides, motivating the exploration of high compositional diversity. How the composition determines the structural chemistry is decisive for the electrochemical performance but very challenging to predict, especially for complex compositions. We introduce the "cationic potential" that captures the key interactions of layered materials and makes it possible to predict the stacking structures. This is demonstrated through the rational design and preparation of layered electrode materials with improved performance. As the stacking structure determines the functional properties, this methodology offers a solution toward the design of alkali metal layered oxides.

Polyoxometalate clusters in minerals: review and complexity analysis.

Most research on polyoxometalates (POMs) has been devoted to synthetic compounds. However, recent mineralogical discoveries of POMs in mineral structures demonstrate their importance in geochemical systems. In total, 15 different types of POM nanoscale-size clusters in minerals are described herein, which occur in 42 different mineral species. The topological diversity of POM clusters in minerals is rather restricted compared to the multitude of moieties reported for synthetic compounds, but the lists of synthetic and natural POMs do not overlap completely. The metal-oxo clusters in the crystal structures of the vanarsite-group minerals ([As3+V4+2V5+10As5+6O51]7-), bouazzerite and whitecapsite ([M3+3Fe7(AsO4)9O8-;n(OH)n]), putnisite ([Cr3+8(OH)16(CO3)8]8-), and ewingite ([(UO2)24(CO3)30O4(OH)12(H2O)8]32-) contain metal-oxo clusters that have no close chemical or topological analogues in synthetic chemistry. The interesting feature of the POM cluster topologies in minerals is the presence of unusual coordination of metal atoms enforced by the topological restraints imposed upon the cluster geometry (the cubic coordination of Fe3+ and Ti4+ ions in arsmirandite and lehmannite, respectively, and the trigonal prismatic coordination of Fe3+ in bouazzerite and whitecapsite). Complexity analysis indicates that ewingite and morrisonite are the first and the second most structurally complex minerals known so far. The formation of nanoscale clusters can be viewed as one of the leading mechanisms of generating structural complexity in both minerals and synthetic inorganic crystalline compounds. The discovery of POM minerals is one of the specific landmarks of descriptive mineralogy and mineralogical crystallography of our time.

Effects of defects and anions on the geometry, electronic structures and exchange interaction of Fe-doped 2H-MoSe2 monolayer

The stability, electronic structure and magnetic properties of Fe doped, Fe-VSe and Fe-NM (NM = B, N) codoped 2H-MoSe2 monolayers with a high concentration of 12.5% are systematically investigated using first-principles calculations. The results show that the Fe dopants are coupled ferromagnetically via p-d exchange mechanism with high d4 spin configuration in the zigzag direction, ascribing to the antiferromagnetic coupling between the localized Fe 3d orbitals and delocalized Se 4p orbitals. Due to large distortion around Fe dopants, the introducing of Se vacancy alters the trigonal prismatic coordination field and causes Hund’s exchange splitting of Fe 3d orbitals, further leading to obvious ferromagnetic coupling and high ferromagnetic stability (ΔEFM-AFM = −724.0 meV) for the Fe-VSe codoped MoSe2 configurations. The non-compensated Fe-NM (NM = B, N) codoping can largely enhance the total moments and structural stability of Fe-doped MoSe2 monolayer due to strong electrostatic attraction and synergistic interaction of anionic dopants. The Fe-doped MoSe2 monolayer is an attractive route to achieve stable room temperature spintronic devices by precise control of synthesis conditions, such as the introducing of Se vacancies and nonmagnetic elements.

A capped trigonal prismatic cobalt(ii) complex as a structural archetype for single-ion magnets.

Two mononuclear, seven-coordinate Co(ii) and Fe(ii) complexes [CoII(BPA-TPA)](BF4)2 (1-Co) and [FeII(BPA-TPA)](ClO4)2 (2-Fe) with a capped trigonal prismatic coordination geometry have been synthesized from the pentapyridyldiamine (BPA-TPA) ligand. 1-Co exhibits easy plane anisotropy in which slow magnetic relaxation is observed under a 1.0 kOe dc field. It is the first example of a single-ion magnet (SIM) of a 3d transition metal ion with a capped trigonal prismatic configuration. 2-Fe is not a SIM at 1.8 K.

Trends in trigonal prismatic Ln-[1]ferrocenophane complexes and discovery of a Ho3+ single-molecule magnet.

Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc3(THF)2Li2]−, of the late trivalent lanthanide ions (Ln = Gd (1), Ho (2), Er (3), Tm (4), Yb (5), Lu (6)). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc2−) average twist angle with decreasing ionic radius (rion) of the central Ln ion, resulting in the largest average Fc2− twist angles for the Lu3+ compound 6. Such high sensitivity of the twist angle to changes in rion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho3+ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM) with barriers to magnetization reversal (U) of 110–131 cm−1. In contrast, compounds featuring Ln ions with prolate electron density (3–5) don't show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2) exchange to yield [HoFc3(THF*)2Li2]− (2-THF*) and [HoFc3(py)2Li2]− (2-py) motifs. We find that larger average Fc2− twist angles (in 2-THF* and 2-py as compared to in 2) result in faster magnetic relaxation times at a given temperature.

Second-order charge-density-wave transition in single crystals of La3Co4Sn13

We present the temperature dependence of the electrical resistivity, the magnetic susceptibility, and the specific heat of a high-quality single crystal of ${\mathrm{La}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$. As opposed to earlier reports on this system, these bulk properties exhibit clear anomalies at the phase transition at ${T}^{*}=151(1)$ K, while the present data confirm the second-order character of this transition. X-ray diffraction with synchrotron radiation is used to solve the fourfold superstructure in space group $I{2}_{1}3$ as it exists below ${T}^{*}$ in the charge-density-wave (CDW) state of ${\mathrm{La}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$. Unlike conventional CDW systems, we have observed hysteresis between the zero-field-cooled and field-cooled magnetization below the CDW transition. This discrepancy can be attributed to a possible magnetic instability arising out of correlations of Co in the lattice, developing at the CDW transition. The crystal structure shows that any modifications of the electronic state of Co might be due to modified binding characteristics of the Sn atoms comprising the trigonal prismatic coordination of Co, while the coordination of Co itself is hardly changed at the phase transition. The superconducting transition is observed at ${T}_{\text{sc}}=2.85(2)$ K. The superconducting energy gap is estimated as 5 K on the basis of the specific heat measured down to 0.1 K. These results suggest that ${\mathrm{La}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$ is a conventional weak-electron-phonon-coupling superconductor.

Synthesis, Crystal Structures and Photoluminescent Properties of One-Dimensional Europium(III)- and Terbium(III)-Glutarate Coordination Polymers, and Their Applications for the Sensing of Fe3+ and Nitroaromatics

Two lanthanide–glutarate coordination polymers, viz. : {[Eu(C5H6O4)(H2O)4]Cl}n, (1) and [Tb(C5H7O4)(C5H6O4)(H2O)2]n, (2) have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, and X-ray crystallography. In 1, the Eu(III) ions are coordinated by four O atoms from two bidentate chelating carboxylate groups, one O atom from a bridging carboxylate group and four O atoms from water molecules adopting an EuO9 distorted tri-capped trigonal prismatic coordination geometry. In 2, the Tb(III) ions are coordinated by six O atoms from three bidentate chelating carboxylates, one O atom from a bridging carboxylate and two O atoms from water molecules to generate distorted tri-capped trigonal prismatic TbO9 polyhedron. In both compounds, the metal polyhedra share edges, producing centrosymmetric Ln2O2 diamonds, and are linked into [001] chains by bridging glutarate di-anions. The crystal structures are consolidated by O–H···O and O–H···Cl hydrogen bonds in 1, and O–H···O hydrogen bonds in 2. Compound 1 exhibits a red emission attributed to the 5D0 → 7FJ (J = 1–4) transitions of the Eu(III) ion, whereas 2 displays green emission corresponding to the 5D4 → 7FJ (J = 0–6) transitions of the Tb(III) ion. Both the compounds exhibit high sensitivity and selectivity for Fe3+ ions due to luminescence quenching compared with other metal ions, which include; Na+, Mg2+, Al3+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+ and Cd2+. Compounds 1 and 2 also show high luminescence quenching sensitivity for 4-nitrophenol over the other aromatic and nitroaromatic compounds, namely; bromobenzene, 1,3-dimethylbenzene, nitrobenzene, 4-nitrotolune, 4-nitrophenol, 2,6-dinitrophenol and 2,4,6-trinitrophenol.

SrIr9In18 – A Structurally Complex Intermetallic Compound with Sr@Ir4In12, Ir@In8 and Ir@In9 Building Units

Single crystals of SrIr9In18 were obtained by induction melting of the elements in a glassy carbon crucible followed by annealing at 1070 K. SrIr9In18 was structurally characterized by X‐ray powder and single crystal diffraction: P4m2, a = 811.21(5), c = 854.49(5) pm, wR2 = 0.0511, 1223 F2 values, and 46 variables. The structure is of a new type. The basic building units are Ir@In8 (distorted square‐prismatic, square anti‐prismatic and bicapped trigonal prismatic coordination) and Ir@In9 (distorted trigonal prismatic coordination) polyhedra, which condense to a three‐dimensional network, which leaves large cavities for the strontium cations, which are coordinated to four iridium and twelve indium atoms. The [Ir9In18]2– polyanionic network is stabilized through Ir–In (267–290 pm) and In–In (302–354 pm) bonding.

Structural Systematics of Lanthanide(III) Picrate Solvates: Adducts of the Carboxamide Ligands Dimethylacetamide and N-Methylpyrrolidinone

The carboxamide-O donor ligands dimethylacetamide (dma) and N-methylpyrrolidinone (nmp) form complexes of lanthanide picrates, Ln(pic)3, of stoichiometry Ln(pic)3(carboxamide)3 in a remarkable variety of phases. Complexes [Ln(pic)3(dma)3], Ln=La, Ce, Nd, Sm, Gd, Yb, Lu, and Y, adopt the 9-coordinate molecular form of tricapped trigonal-prismatic coordination geometry seen to predominate, as two stereoisomers, in related species involving dimethylsulfoxide (dmso), trimethylphosphate (tmp), and hexamethylphosphoramide (hmpa) but as four different phases (depending on Ln), none of which is the same as for the previously known La complex. For Ln=Pr, 9-coordinate species of composition [Pr(pic)3(dma)2(alcohol)] (alcohol=ethanol and propan-2-ol) have been characterised and a low quality determination indicates that a similar species (with propan-2-ol) is formed by Y. For nmp, the composition [Ln(pic)3(nmp)3] is maintained across the series for Ln=La, Ce, Pr, Nd, Gd, Er, Tm, Yb, and Lu but 9-coordination is not for Ln=Er, Tm, Yb, and Lu. A decreased coordination there is a result of one or two picrate ligands acting as phenoxide-O donors only, a marked contrast with the analogous Ln(pic)3 complexes with dmso, tmp, hmpa, and dma, where picrate chelation is universal, but with some parallel to related ScIII complexes. Several polymorph pairs can be identified among the nmp complexes.

Structural Systematics of Lanthanide(III) Picrate Solvates: Hexamethylphosphoramide and Octamethylpyrophosphoramide Adducts

Crystalline products of the reactions of lanthanide picrates, Ln(pic)3 (pic=2,4,6-trinitrophenoxide), with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) have been characterised by single-crystal X-ray diffraction studies. With hmpa and lighter lanthanides (La, Sm, Eu), isomorphous species (monoclinic, P21/c, Z 4) of stoichiometry [Ln(pic)3(hmpa)3]·0.5H2O, have been defined where the molecular units in the lattice contain 9-coordinate Ln with tricapped trigonal-prismatic coordination geometry. The picrate ligands are bidentate through phenoxide-O and 2-nitro-O, with the latter occupying the capping positions, while the hmpa ligands are singly O-bound to one trigonal face. Heavier lanthanides (Gd, Lu) and Y have been found to give isomorphous (monoclinic, P21/n, Z 4) species of stoichiometry [Ln(pic)3(hmpa)2], with 8-coordinate Ln of an irregular geometry best considered as close to that of a bicapped trigonal-prism. The picrate ligands chelate in the same manner as in the lighter Ln complexes but with one spanning a trigonal edge, and the hmpa-O donors occuping two apices of the other trigonal face. The ligand ompa has been found to act as a bidentate chelate in all isolated species, displacing one picrate from the metal ion coordination sphere to give ionic complexes. For La, Nd, and Gd, isomorphous (monoclinic, P21/n, Z 4) complexes of stoichiometry [Ln(pic)2(ompa)2(OH2)](pic)·0.5H2O containing 9-coordinate, tricapped trigonal-prismatic Ln with a single aqua ligand have been defined, while for Er, Yb, Lu, and Y, both the coordinated and lattice water molecules are lost in isomorphous (monoclininc, P21/c, Z 8) 8-coordinate, square-antiprismatic species of stoichiometry [Ln(pic)2(ompa)2](pic). For Er, further polymorphs, one monoclinic, P21/c, and the other triclinic, , have also been characterised.

Polymorphism and photoluminescence properties of K3ErSi2O7.

Two polymorphs of tripotassium erbium disilicate, K3ErSi2O7, were synthesized by high-temperature flux crystal growth during the exploration of the flux technique for growing new alkali rare-earth elements (REE) containing silicates. Their crystal structures were determined by single-crystal X-ray diffraction analysis. One of them (denoted 1) crystallizes in the space group P63/mmc and is isostructural with disilicates K3LuSi2O7, K3ScSi2O7 and K3YSi2O7, while the other (denoted 2) crystallizes in the space group P63/mcm and is isostructural with disilicates K3NdSi2O7, K3REESi2O7 (REE= Gd-Yb), K3YSi2O7, K3(Y0.9Dy0.1)Si2O7 and K3SmSi2O7. In the crystal structure of polymorph 1, the Er cations are in an almost perfect octahedral coordination, while in the crystal structure of polymorph 2, part of the Er cations are in a slightly distorted octahedral coordination and the other part are in an ideal trigonal prismatic coordination environment. Sharing six corners, disilicate Si2O7 groups in the crystal structure of polymorph 1 link six ErO6 octahedra, forming a three-dimensional network and nine-coordinated potassium cations are located in its holes. In the crystal structure of polymorph 2, the disilicate Si2O7 groups connect four ErO6 octahedra, as well as one ErO6 trigonal prism. Three differently coordinated potassium cations are situated between them. Different site symmetries of the erbium cations in the crystal structures of polymorphs 1 and 2 affect their photoluminescence properties. Only polymorph 2 exhibits luminescence. Intense narrow lines in the emission spectrum are a result of the 4f-4f transition. The green emission line at 560 nm is the result of the Er3+ transition 4S3/2→4I15/2, and the luminescence line at 690 nm is the result of a 4F9/2→4I15/2 transition. The crystal morphologies of the two polymorphs are similar. Crystals of polymorph 1 are in the form of a hexagonal prism in combination with a hexagonal base, while crystals of polymorph 2 contain a dihexagonal prism in combination with a hexagonal base, although poorly developed faces of the dihexagonal pyramid can also be noticed.

Luminescent Pr(III)-Based Coordination Polymer: Syntheses, Structures, N2 and CO2 Adsorption Properties

A new Pr(III)-based metal organic framework with formula {[Pr2(C8H3O6N)(SO4)2]·5H2O}n was hydrothermally synthesized and characterized by techniques of single crystal X-ray diffraction, infrared spectra (IR), thermogravimetric analysis (TGA), elemental analysis, powder X-ray diffraction (PXRD), and luminescent measurements. X-ray crystal structure analyses reveal that complex 1 is binuclear structure and all Pr(III) atoms show a coordination number of nine with a tricapped trigonal prismatic coordination geometry. Throughout the molecular structure, this lanthanide metal–organic frameworks exhibits a 3D architecture built by the 1D double-stranded chains of Pr ions linked by the 5-nitroisophthalic acid ligand and 2D Pr–SO42− grid. In addition, the fluorescence, nitrogen adsorption properties and carbon dioxide adsorption properties of complex 1 were also investigated. The results indicate that the complex is not only a luminescent and mesoporous material, but also a potential material for selective absorption of carbon dioxide.

Synthesis and Properties of (BiSe)0.97MoSe2: A Heterostructure Containing Both 2H-MoSe2 and 1T-MoSe2

The metastable heterostructure, (BiSe)0.97MoSe2, containing alternating bilayers of BiSe and MoSe2 trilayers was synthesized using the modulated elemental reactant method to determine if charge transfer from BiSe to MoSe2 would stabilize the metallic 1T polymorph of MoSe2. Optimum synthesis conditions were determined by following the structural evolution as a function of temperature. The structure of the product contained distorted rock salt-structured BiSe layers alternating with hexagonal MoSe2 layers. High-angle annular dark field scanning transmission electron microscopy images revealed that two different polymorphs of MoSe2 coexisted in (BiSe)0.97MoSe2. Raman spectroscopy confirmed the presence of 1T MoSe2 layers. X-ray photoelectron spectroscopy (XPS) indicated that there were two different electronic states for both Mo and Bi. The Mo states are consistent with having octahedral and trigonal prismatic coordination of molybdenum as found in the 1T and 2H polymorphs of MoSe2. The two different electro...

Dynamic solution behaviour of metal complexes of the hexaamine cage ligand Me8tricosane

The solid state structures of the hexaamine cage complexes [M(Me8tricosane)]2+ (M = Zn, Cd, Hg) were previously shown to feature highly symmetric octahedral or trigonal prismatic coordination geometries. Here we show that the solution NMR spectra of each of these three complexes are far more complex than what would be expected if the solid state structures were retained after dissolution. The large numbers of resonances observed in the solution NMR spectra reflects establishment of equilibria involving multiple diastereoisomers with different nitrogen atom configurations. Support for this explanation was provided by the 15N HSQC spectrum of the Zn complex, and by variable temperature 1H and 13C NMR spectra of each of the three metal complexes. In addition, the results of calculations performed using DFT methods showed that the differences in energy between diastereoisomers were sometimes very small, and therefore unlikely to present a significant barrier to isomerisation processes.

Charge density wave and spin 1/2 insulating state in single layer 1T-NbS2

In bulk samples and few layer flakes, the transition metal dichalcogenides NbS2 and NbSe2 assume the H polytype structure with trigonal prismatic coordination of the Nb atom. Recently, however, single and few layers of 1T-NbSe2 with octahedral coordination around the transition metal ion were synthesized. Motivated by these experiments and by using first-principles calculations, we investigate the structural, electronic and dynamical properties of single layer 1T-NbS2. We find that single-layer 1T-NbS2 undergoes a star-of-David charge density wave. Within the generalized gradient approximation, the weak interaction between the stars leads to an ultraflat band that results to be located at the Fermi level and isolated from all other bands. The spin-polarized generalized gradient approximation stabilizes a total spin 1/2 magnetic state with a magnetic moment localized on the central Nb in the star and the opening of a 0.15 eV band gap. In the GGA + U framework, the magnetic moment on the central Nb is enhanced to and a larger gap occurs. Most important, this approximation gives a small energy difference between the 1T and 1H polytypes (only +0.5 mRy/Nb), suggesting that the 1T-polytype can be synthesized in a similar way as done for single layer 1T-NbSe2. Finally we compute first and second nearest neighbors magnetic inter-star exchange interactions finding J1 = 9.5 K and J2 = 0.4 K ferromagnetic coupling constants.

The rare earth metal hydride tellurides REHTe (RE=Y, La–Nd, Gd–Er)

Abstract The synthesis and crystal structure of a series of rare earth metal hydride tellurides with the composition REHTe (RE = Y, La–Nd, Gd–Er) is reported. These compounds have been obtained by the reaction of rare earth metal dihydrides (REH2) with elemental tellurium in sealed tantalum capsules at T = 700°C using cesium chloride (CsCl) as fluxing agent, which can be washed away with water due to the astonishing insensitivity of these hydride tellurides (REHTe) against hydrolysis. All of the compounds crystallize in the hexagonal space group P6̅m2 with a filled WC-type crystal structure, exhibiting a mutual trigonal-prismatic coordination of the heavy ions (RE 3+ and Te2−), while the hydride anions reside in the trigonal prismatic voids surrounded by three rare earth metal cations expanding their coordination pattern to a tricapped trigonal prism. This 1H-type crystal structure is compared with the 1H- and 2H-type structures of the respective hydride selenides (REHSe, RE = Y, La–Nd, Gd–Tm, Lu). Both hexagonal basic crystal structures can be derived from the AlB2-type structure as demonstrated in a Bärnighausen tree by group-subgroup relationships.

Black Current: Structure, Characterization, and Optoelectronic Properties of Ce3 Cl3 [MoO6

The admixture of CeO2 , Ce, CeCl3 , and MoO3 with an excess of LiCl as flux in evacuated silica ampules leads to large black single crystals as well as a black microcrystalline powder of Ce3 Cl3 [MoO6 ] after tempering at 850 °C for three days. The title compound crystallizes in the hexagonal space group P63 /m (a=934.93(4), c=538.86(2) pm) with two formula units per unit cell. The crystal structure consists of rather unusual trigonal-prismatic [MoO6 ]6- units besides Ce3+ ions in a tetra-capped trigonal-prismatic coordination, formed by four Cl- and six O2- ions. The black color is related to an optical band gap of 1.35(2) eV, which was determined by diffuse reflectance spectroscopy and confirmed by theoretical calculations. The low band gap between the 4f1 state of cerium (HOMO) and the 5d0 state of molybdenum (LUMO) gave rise to the idea of electronic excitation between these two states by IR irradiation, creating a drop in the resistivity of the material, which was detected by appropriate measurements.