Na[GeF5]·2HF: the first quarternary phase in the H-Na-Ge-F system.

The structure of cis- or trans-bridged [GeF5]- anionic chains have been investigated [Mallouk et al. (1984). Inorg. Chem. 23, 3160-3166] showing the first crystal structures of µ-F-bridged pentafluorogermanates. Herein, we report the second crystal structure of trans-pentafluorogermanate anions present in the crystal structure of sodium trans-pentafluorogermanate(IV) bis(hydrogen fluoride), Na[GeF5]·2HF. The crystal structure [orthorhombic Pca21, a = 12.3786 (3), b = 7.2189 (2), c = 11.4969 (3) Šand Z = 8] is built up from infinite chains of trans-linked [GeF6]2- octahedra, extending along the b axis and spanning a network of pentagonal bipyramidal distorted Na-centred polyhedra. These [NaF7] polyhedra are linked in a trans-edge fashion via hydrogen fluoride molecules, in analogy to already known sodium hydrogen fluorides and potassium hydrogen fluorides.

Three Ways to (Pseudo)cubic Structure Models: Phase Transition and Pseudosymmetry in Orthorhombic Cs3MO4 (M = V, Nb, or Ta).

The new oxometalates Cs3NbO4 and Cs3TaO4 together with Cs3VO4 crystallize with the K3NO4 structure type [Pnma, a = 12.495(2) Å, b = 9.0183(14) Å, and c = 6.6529(10) Å for the V compound; a = 12.928(2) Å, b = 9.177(3) Å, and c = 6.739(4) Å for the Nb; and a = 12.963(4) Å, b = 9.122(2) Å, and c = 6.774(1) Å for the Ta compound]. Their crystal structures were evaluated on the basis of single-crystal and powder X-ray diffractometry, assisted by vibrational spectroscopy, thermoanalysis, and DFT calculations. The crystal structures contain tetrahedral [M5+O4]3- anions, representing the first occurrence of Nb and Ta in a tetrahedral oxidic environment. Many representatives of the orthorhombic K3NO4 structure type have been described in the literature with a cubic structure model with disordered O atomic positions. Based on studies on Cs3MO4 (M = P, V, Nb, or Ta), we show here three different effects which can lead to (pseudo)cubic data sets. Two of them are problems of crystallographic nature (overlooked twinning or adverse atomic form factor ratios), but the third one, phase transformation into a plastic crystalline high-temperature modification, leads to a "truly" cubic structure with dynamically disordered (freely rotating) oxometalate anions. This might be of interest with respect to a large and growing number of sulfido- and selenidometalate materials which are today in discussion as solid-state electrolytes and to the mechanism of the unusually efficient ion transport therein.

Influence of Disorder on the Bad Metal Behavior in Polar Amalgams.

The two new ternary amalgams K1-xRbxHg11 [x = 0.472(7)] and Cs3-xCaxHg20 [x = 0.20(3)] represent two different examples of how to create ternary compounds from binaries by statistical atom substitution. K1-xRbxHg11 is a Vegard-type mixed crystal of the isostructural binaries KHg11 and RbHg11 [cubic, BaHg11 structure type, space group Pm3̅m, a = 9.69143(3) Å, Rietveld refinement], whereas Cs3-xCaxHg20 is a substitution variant of the Rb3Hg20 structure type [cubic, space group Pm3̅n, a = 10.89553(14) Å, Rietveld refinement] for which a fully substituted isostructural binary Ca phase is unknown. In K1-xRbxHg11, the valence electron concentration (VEC) is not changed by the substitution, whereas in Cs3-xCaxHg20, the VEC increases with the Ca content. Amalgams of electropositive metals form polar metal bonds and show "bad metal" properties. By thermal analysis, magnetic susceptibility and resistivity measurements, and density functional theory calculations of the electronic structures, we investigate the effect of the structural disorder introduced by creating mixed-atom occupation on the physical properties of the two new polar amalgam systems.

Polymorphism and Fast Potassium-Ion Conduction in the T5 Supertetrahedral Phosphidosilicate KSi2 P3.

The all-solid-state battery (ASSB) is a promising candidate for electrochemical energy storage. In view of the limited availability of lithium, however, alternative systems based on earth-abundant and inexpensive elements are urgently sought. Besides well-studied sodium compounds, potassium-based systems offer the advantage of low cost and a large electrochemical window, but are hardly explored. Here we report the synthesis and crystal structure of K-ion conducting T5 KSi2 P3 inspired by recent discoveries of fast ion conductors in alkaline phosphidosilicates. KSi2 P3 is composed of SiP4 tetrahedra forming interpenetrating networks of large T5 supertetrahedra. The compound passes through a reconstructive phase transition from the known T3 to the new tetragonal T5 polymorph at 1020 °C with enantiotropic displacive phase transitions upon cooling at about 155 °C and 80 °C. The potassium ions are located in large channels between the T5 supertetrahedral networks and show facile movement through the structure. The bulk ionic conductivity is up to 2.6×10-4  S cm-1 at 25 °C with an average activation energy of 0.20 eV. This is remarkably high for a potassium ion conductor at room temperature, and marks KSi2 P3 as the first non-oxide solid potassium ion conductor.

Electrochemical Synthesis and Crystal Structure of the Organic Ion Intercalated Superconductor (TMA)0.5Fe2Se2 with Tc = 43 K.

Intercalation of organic cations in superconducting iron selenide can significantly increase the critical temperature (Tc). We present an electrochemical method using ß-FeSe crystals (Tc ≈ 8 K) floating on a mercury cathode to intercalate tetramethylammonium ions (TMA+) quantitatively to obtain bulk samples of (TMA)0.5Fe2Se2 with Tc = 43 K. The layered crystal structure is closely related to the ThCr2Si2-type with disordered TMA+ ions between the FeSe layers. Although the organic ions are not detectable by X-ray diffraction, packing requirements as well as first-principle density functional theory calculations constrain the specified structure. Our synthetic route enables electrochemical intercalations of other organic cations with high yields to greatly optimize the superconducting properties and to expand this class of high-Tc materials.

Synthesis and Crystal Structure of Three Ga-rich Lithium Gallides, LiGa6, Li11Ga24, and LiGa2.

Three new binary phases have been synthesized in the Ga-rich part of the Li-Ga system: LiGa6, Li11Ga24, and LiGa2. Their crystal structures and the respective phase formation conditions have been investigated with X-ray single crystal structure refinements, Rietveld refinements of X-ray powder diffraction data, and thermal analyses. They complete the Ga-rich part of the Li-Ga phase diagram together with the reported phases Li6-xGa14 with 2 ≤ x ≤ 3 and LiGa3.42. The compositions of two of the new gallides, LiGa6 and LiGa2, had been predicted in previous thermoanalytical studies, but their crystal structures remained unknown. All three new binary main group compounds adopt new structure types. LiGa6 crystallizes with the trigonal space group R3̅c (No. 167, a = 6.1851(8) Å, c = 23.467(4) Å), Li11Ga24 crystallizes with the hexagonal space group P63mc (No. 186, a = 13.7700(19) Å, c = 23.250(5) Å), and LiGa2 crystallizes with the orthorhombic space group Cmce (No. 64, a = 8.51953(4) Å, b = 14.44163(7) Å, c = 15.29226(7) Å). All phases form air- and moisture-sensitive crystals of bright metallic luster. They can be synthesized starting from the pure elements and taking into account their incongruent melting behavior by adequate tempering sequences derived from differential scanning calorimetry (DSC) studies of the system. Lithium gallides do not form electron-precise Zintl phases. The electronic structures of these polar intermetallic phases combine ionic, covalent, and metallic bonding contributions and have been analyzed by density functional theory (DFT) calculations in the cases of LiGa6 and LiGa2. Measurements of the specific electronic resistivities have also been performed and prove the metallic behavior.

Finding the Right Blend: Interplay Between Structure and Sodium Ion Conductivity in the System Na5AlS4-Na4SiS4.

The rational design of high performance sodium solid electrolytes is one of the key challenges in modern battery research. In this work, we identify new sodium ion conductors in the substitution series Na5-x Al1-x Si x S4 (0 ≤ x ≤ 1), which are entirely based on earth-abundant elements. These compounds exhibit conductivities ranging from 1.64 · 10-7 for Na4SiS4 to 2.04 · 10-5 for Na8.5(AlS4)0.5(SiS4)1.5 (x = 0.75). We determined the crystal structures of the Na+-ion conductors Na4SiS4 as well as hitherto unknown Na5AlS4 and Na9(AlS4)(SiS4). Na+-ion conduction pathways were calculated by bond valence energy landscape (BVEL) calculations for all new structures highlighting the influence of the local coordination symmetry of sodium ions on the energy landscape within this family. Our findings show that the interplay of charge carrier concentration and low site symmetry of sodium ions can enhance the conductivity by several orders of magnitude.

Cu9.1Te4Cl3: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity.

Cu9.1Te4Cl3 is a new polymorphic compound in the class of coinage metal polytelluride halides. Copper is highly mobile, which results in multiple order-disorder phase transitions in a limited temperature interval from 240 to 370 K. Mainly as a consequence of thermal transport properties, the compound's thermoelectric figure of merit reaches values up to ZT = 0.15 in the temperature range between room temperature and 523 K. Its structure is closely related to that of Ag10Te4Br3, another coinage metal polytelluride halide, which represents the first p-n-p-switchable semiconductor approachable by a simple temperature change. The title compound outperforms Ag10Te4Br3 in terms of thermoelectric properties by 1 order of magnitude and therefore acts as a link between the class of p-n-p compounds and thermoelectric materials.

Oxonitridosilicate Oxides RE26Ba6[Si22O19N36]O16:Eu2+ (RE = Y, Tb) with a Unique Layered Structure and Orange-Red Luminescence for RE = Y.

The oxonitridosilicate oxides RE26Ba6[Si22O19N36]O16:Eu2+ (RE = Y, Tb) were synthesized by high-temperature reaction in a radiofrequency furnace starting from REF3, RE2O3 (RE = Y, Tb), BaH2, Si(NH)2, and EuF3. The structure elucidation is based on single-crystal X-ray data. The isotypic materials crystallize in the monoclinic space group Pm (no. 6) [Z = 3, a = 16.4285(8), b = 20.8423(9), c = 16.9257(8) Å, ß = 119.006(3)° for RE = Y and a = 16.5465(7), b = 20.9328(9), c = 17.0038(7) Å, ß = 119.103(2)° for RE = Tb]. The unique silicate layers are made up from Q1-, Q2-, and Q3-type Si(O/N)4- as well as Q4-type SiN4-tetrahedra, forming three slightly differing types of cages. The corresponding 3-fold superstructure as well as pronounced hexagonal pseudosymmetry complicated the structure elucidation. Rietveld refinement on powder X-ray diffraction data, energy-dispersive X-ray spectroscopy and infrared spectroscopy support the findings from single-crystal X-ray data. When excited with UV to blue light, Y26Ba6[Si22O19N36]O16:Eu2+ shows broad orange-red luminescence (λem = 628 nm, fwhm ≈ 125 nm/3130 cm-1). An optical band gap of 4.2 eV was determined for the doped compound by means of UV/vis spectroscopy.

NMR interaction tensors of 51V and 207Pb in vanadinite, Pb5(VO4)3Cl, determined from DFT calculations and single-crystal NMR measurements, using only one general rotation axis.

Orientation-dependent NMR spectra of a single crystal of the mineral vanadinite, Pb5(VO4)3Cl, were acquired using only one rotation axis with a general orientation in the hexagonal crystal lattice (space group P63/m). The chemical shift (CS) tensors for the 207Pb on Wyckoff positions 6h and 4f, and both CS and quadrupole coupling tensor Q for 51V at the positions 6h were determined by including the NMR response of symmetry-related atoms in the unit cell (and in case of 207Pb at 4f, also the isotropic shift from MAS NMR spectra). This previously suggested 'single rotation method' greatly reduces the necessary amount of data acquisition and analysis. The precise orientation of the rotation axis could not be found by X-ray diffraction experiments because of the high linear absorption coefficient of vanadinite, which is chiefly due to its high lead content. The axis orientation was therefore included into the multi-parameter data fit routine. This NMR-based approach is widely applicable, and offers an alternative way of orienting single crystals. The NMR parameters derived from the tensor eigenvalues are δiso=(-1729±9) ppm, Δδ=(-1071±5) ppm, ηCS=0.362±0.008 for 207Pb at positions 6h, and δiso=(-1619±2) ppm, Δδ=(-780±58) ppm, ηCS=0.06±0.08 for positions 4f. For 51V, δiso=(-509±3) ppm, Δδ=(-37±2) ppm, ηCS=0.78±0.09, with the quadrupolar coupling described by χ=(2.52±0.01) MHz and ηQ=0.047±0.003. In contrast to the precisely determined tensor eigenvalues, the orientation of the eigenvectors in the crystal ab -plane of the vanadinite system could only be resolved by resorting to data obtained from density functional theory (DFT) calculations.

The Triple Salt Sr14[Ta4N13][TaN4]O-A Nitridotantalate Oxide with 19-fold Rock Salt Superstructure.

A new structure motif in nitridometalate chemistry is the tetracatena-nitridotantalate anion [Ta4N13]19-. It occurs in the crystal structure of the triple salt Sr14[Ta4N13][TaN4]O (monoclinic, space group P21/c with a = 15.062(2) Å, b = 7.2484(6) Å, c = 24.266(3) Å, and ß = 97.280(10)o) together with ortho-tantalate and isolated oxide anions. Synthesis followed a new approach with employment of Sr surplus and reductive conditions aimed at the preparation of subvalent compounds. The new structure type was established on the basis of single-crystal X-ray diffraction data and also Rietveld refinement. It is a complex superstructure of the rock salt structure type with Ta and Sr atoms forming the face-centered cubic packing and N and O atoms occupying 18/19 of the octahedral voids. We discuss structure and stability of the triple salt with respect to other known nitridometalates and the use of this triple salt for preparative access toward new metal-rich compounds in this field.

Electrocrystallization: A Synthetic Method for Intermetallic Phases with Polar Metal-Metal Bonding.

Isothermal electrolysis is a convenient preparation technique for a large number of intermetallic phases. A solution of the salt of a less-noble metal is electrolyzed on a cathode consisting of a liquid metal or intermetallic system. This yields crystalline products at mild reaction conditions in a few hours. We show the aptness and the limitations of this approach. First, we give an introduction into the relevance of electrolytic synthesis for chemistry. Then we present materials and techniques our group has developed for electrocrystallization that are useful for electrochemical syntheses in general. Subsequently, we discuss different phase formation eventualities and propose basic rationalization concepts, illustrated with examples from our work. The scope of this report is to present electrocrystallization as a well-known yet underestimated synthetic process, especially in intermetallic chemistry. For this purpose we adduce literature examples (Li3Ga14, NaGa4, K8Ga8Sn38), technical advice, basic concepts, and new crystal structures only available by this method: Li3Ga13Sn and CsIn12. Electrocrystallization has recently proven especially helpful in our work concerning synthesis of intermetallic phases with polar metal-metal bonding, especially Hg-rich amalgams of less-noble metals. With the term "polar metal-metal bonding" we describe phases where the constituting elements have large electronegativity difference and yet show incomplete electron transfer from the less-noble to the nobler metal. This distinguishes polar intermetallic phases from classical Zintl phases where the electron transfer is virtually complete. Polar metallic phases can show "bad metal behavior" and interesting combinations of ionic and metallic properties. Amalgams of less-noble metals are preeminent representatives for this class of intermetallic phases as Hg is the only noble metal with endothermic electron affinity and thus a very low tendency toward anion formation. To illustrate both the aptness of the electrocrystallization process and our interest in polar metals in the above-mentioned sense, we present amalgams but also Hg-free intermetallics.

Chemical Twinning of Salt and Metal in the Subnitridometalates Ba23 Na11 (MN4 )4 with M=V, Nb, Ta.

The subnitridometalates Ba23 Na11 (MN4 )4 (M=V, Nb, Ta) crystallize in a new structure type, which shows ionic ortho-nitridometalate anions and motifs from simple (inter)metallic packings: Na-centered [Na8 ] cubes as cutouts of the bcc structure of elemental Na and Na-centered [Ba10 Na2 ] icosahedra as found in Laves phases, for example. Single-crystal and powder X-ray diffraction studies in combination with quantum-chemical calculations of the electronic structure and Raman spectroscopy support the characterization of the subnitridometalates as "chemical twins". They consist of independent building units with locally prevalent ionic or metallic bonding in an overall metallic compound.

M2PO3N (M = Ca, Sr): ortho-Oxonitridophosphates with ß-K2SO4 Structure Type.

Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 °C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 °C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) Å, b = 5.5778(3) Å, c = 9.8132(7) Å, R1 = 0.020, wR2 = 0.047] crystallizes in the ß-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(α00)0ss [Z = 4, a = 6.7942(7) Å, b = 5.4392(6) Å, c = 9.4158(11) Å, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu(2+), Ca2PO3N exhibits luminescence in the green range (λem = 525 nm) of the visible spectrum if excited by near-UV light (λexc = 400 nm).

Structural chemistry and number theory amalgamized: crystal structure of Na11Hg52.

The recently elucidated crystal structure of the technologically important amalgam Na11Hg52 is described by means of a method employing some fundamental concept of number theory, namely modular arithmetical (congruence) relations observed between a slightly idealized set of atomic coordinates. In combination with well known ideas from group theory, regarding lattice-sublattice transformations, these allow for a deeper mutual understanding of both and provide the structural chemist with a slightly different kind of spectacles, thus enabling a distinct viw on complex crystal structures in general.

Alkali Metal Suboxometalates-Structural Chemistry between Salts and Metals.

The crystal structures of the new cesium-poor alkali metal suboxometalates Cs10MO5 (M = Al, Ga, Fe) show both metallic and ionic bonding following the formal description (Cs(+))10(MO4(5-))(O(2-))·3e(-). Comparable to the cesium-rich suboxometalates Cs9MO4 (M = Al, Ga, In, Fe, Sc) with ionic subdivision (Cs(+))9(MO4(5-))·4e(-), they contain an oxometalate anion [M(III)O4](5-) embedded in a metallic matrix of cesium atoms. Columnlike building units form with prevalent ionic bonding inside and metallic bonding on the outer surface. In the cesium-rich suboxometalates Cs9MO4, additional cesium atoms with no contact to any anion are inserted between columns of the formal composition [Cs8MO4]. In the cesium-poor suboxometalates Cs10MO5, the same columns are extended by face-sharing [Cs6O] units, and no additional cesium atoms are present. The terms "cesium-rich" and "cesium-poor" here refer to the Cs:O ratio. The new suboxometalates Cs10MO5 crystallize in two modifications with new structure types. The orthorhombic modification adopts a structure with four formula units per unit cell in space group Pnnm with a = 11.158(3) Å, b = 23.693(15) Å, and c = 12.229(3) Å for Cs10AlO5. The monoclinic modification crystallizes with eight formula units per unit cell in space group C2/c with a = 21.195(3) Å, b = 12.480(1) Å, c = 24.120(4) Å, and ß = 98.06(1)° for Cs10AlO5. Limits to phase formation are given by the restriction that the M atoms must be trivalent and by geometric size restrictions for the insertion of [Cs6O] blocks in Cs10MO5. All of the suboxometalate structures show similar structural details and form mixed crystal series with statistical occupation for the M elements following the patterns Cs9(M(1)xM(2)1-x)O4 and Cs10(M(1)xM(2)1-x)O5. The suboxometalates are a new example of ordered intergrowth of ionic and metallic structure elements, allowing for the combination of properties related to both ionic and metallic materials.

Redetermination of [EuCl2(H2O)6]Cl.

The crystal structure of the title compound, hexa-aqua-dichlorido-europium(III) chloride, was redetermined with modern crystallographic methods. In comparison with the previous study [Lepert et al. (1983 ▶). Aust. J. Chem. 36, 477-482], it could be shown that the atomic coordinates of some O atoms had been confused and now were corrected. Moreover, it was possible to freely refine the positions of the H atoms and thus to improve the accurracy of the crystal structure. [EuCl2(H2O)6]Cl crystallizes with the GdCl3·6H2O structure-type, exhibiting discrete [EuCl2(H2O)6](+) cations as the main building blocks. The main blocks are linked with isolated chloride anions via O-H⋯Cl hydrogen bonds into a three-dimensional framework. The Eu(3+) cation is located on a twofold rotation axis and is coordinated in the form of a Cl2O6 square anti-prism. One chloride anion coordinates directly to Eu(3+), whereas the other chloride anion, situated on a twofold rotation axis, is hydrogen bonded to six octa-hedrally arranged water mol-ecules.

A five-membered Ru5 ring in a hexagonal La14 cage: the La14Cl20Ru5 structure.

The title compound features a five-membered Ru(5) ring embedded in a La(14) hexagonal wheel-like cage, an incommensurate combination of the two building units. A formal electron partition of (La(3+))(14)(Cl(-))(20)(Ru(5))(22-) results in a (Ru(5))(22-) ring isoelectronic to (Cd(5))(2-). However, computational studies show that there is significant electron back-donation from the Ru(5) ring to the La(14) wheel. This interaction strongly stabilizes the Ru(5) ring. The resistivity and magnetic susceptibility of the compound have also been investigated.

Suboxides with complex anions: the suboxoindate Cs9InO4.

Salty metal: In the suboxometallate Cs(9)InO(4), metallic cesium columns (see picture; blue) lie next to ionic oxoindate(III) columns. The chemistry of the suboxides is thus expanded to structures containing complex anions.