K3Mo2O5.6F3.4 and K3V2O3.3F5.7 - exploring transition metal cation valence and anion distribution in oxyfluorides

Oxyfluorides come in many different structures and are highly adaptable in composition, not least because of their mixed-anionic nature. Slight changes, unless specifically looked for, can easily go unnoticed. In this paper, we present two oxyfluorides, K3Mo2O5.6F3.4 and K3V2O3.3F5.7, synthesized under high-pressure/high-temperature conditions, and demonstrate the importance of careful analysis of composition, oxidation state and O/F anion distribution for an accurate description of oxyfluorides. Their crystal structures were determined by single-crystal X-ray diffraction and the transition metal cation valences analyzed by X-ray photoelectron spectroscopy (XPS). The O/F anion ratio was calculated using the principle of charge neutrality and the local distribution within the crystallographic framework was studied using bond valence (BV) and charge distribution (CHARDI) calculations. Madelung Part of Lattice Energy (MAPLE) calculations and magnetic measurements provide insight into phase stability and corroborate the mixed-valent nature of the compounds.

Pressure-Assisted Synthesis of Highly Crystalline 1T''-Lix MoS2

Lix MoS2 is not only a lithium battery material, but is also an important precursor for the synthesis of MoS2 nanomaterials. Current syntheses of MoS2 , such as in n-butyllithium/LiBH4 or electrochemically, are not satisfying in terms of defined stoichiometry and crystallinity, so an accurate experimental crystal structure determination of this important and widely used material has been long awaited. A high-pressure/high-temperature synthesis yielded highly crystalline 1T''-Lix MoS2 (x=1, 1.333). 1T''-LiMoS2 crystallizes in the space group P1 ‾ $\bar 1$ with a=6.2482(3) Å, b=6.6336(3) Å, c=6.7480(3) Å, α=119.321(2)°, β=90.010(2)° and γ=90.077(2)°. The arrangement of Mo atoms within the b-c-plane confirmed a predicted Peierls distortion. A similar atom distribution pattern to that of Mo is also observed for the lithium atoms. Calculation of bond valence site energies gave an activation barrier of 1.244 eV for 2D lithium-ion migration. For x=1.333, a phase-pure synthesis was achieved.

Pressure-Induced Dislocations and Their Influence on Ionic Transport in Li+-Conducting Argyrodites

The influence of the microstructure on the ionic conductivity and cell performance is a topic of broad scientific interest in solid-state batteries. The current understanding is that interfacial decomposition reactions during cycling induce local strain at the interfaces between solid electrolytes and the anode/cathode, as well as within the electrode composites. Characterizing the effects of internal strain on ion transport is particularly important, given the significant local chemomechanical effects caused by volumetric changes of the active materials during cycling. Here, we show the effects of internal strain on the bulk ionic transport of the argyrodite Li6PS5Br. Internal strain is reproducibly induced by applying pressures with values up to 10 GPa. An internal permanent strain is observed in the material, indicating long-range strain fields typical for dislocations. With increasing dislocation densities, an increase in the lithium ionic conductivity can be observed that extends into improved ionic transport in solid-state battery electrode composites. This work shows the potential of strain engineering as an additional approach for tuning ion conductors without changing the composition of the material itself.

A new high-pressure polymorph of K2MoO2F4

In this paper, a new high-pressure (HP) polymorph of the otherwise known oxyfluoride K2MoO2F4 is presented. The crystal structure was determined by use of single-crystal X-ray diffractometry and its features are described in detail herein. HP-K2MoO2F4 crystallizes in the monoclinic space group C2/m (no. 12) with the cell parameters a = 13.8579(5), b = 5.8109(2), c = 6.9442(3) Å, β = 90.36(1)°, V = 559.18(4) Å3, and Z = 4 at T = 301(2) K. Bond valence (BV) and charge distribution (CHARDI) calculations were carried out to support the assignment of oxygen and fluorine to the various anion positions and Madelung part of lattice energy (MAPLE) calculations were used to validate the structure model. Infrared spectroscopy provided further information on the structure and water content of the inseparable side phase.

Photoluminescence of Mn2+ in the Borosulfate Zn[B2 (SO4 )4 ] : Mn2+ -A Tool to Detect Weak Coordination Behavior of Ligands

The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in, e.g., phosphor-converted white light-emitting diodes (pc-wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5 -3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal-ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer-like borosulfate ligand in the Mn2+ -containing solid solutions Zn1-x Mnx [B2 (SO4 )4 ] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2 (SO4 )4 ]:Mn2+ shows orange narrow-band luminescence at 590 nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn-O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal-ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors.

High-Pressure and High-Temperature Dion-Jacobson Layered Perovskite Polymorphs of KWO3 F

Two new Dion-Jacobson layered perovskite polymorphs of the known oxyfluoride compound KWO3 F are reported. A high-pressure modification was synthesized using a multianvil setup and subsequently transformed into a high-temperature phase at ∼311 °C. The crystal structures of both polymorphs were determined by use of single-crystal X-ray diffraction and are described in detail herein. Differential thermal analyses and thermogravimetric analyses were carried out to further investigate the phase transition characteristics. Bond valence (BV) and charge distribution (CHARDI) calculations confirm the occupancy of mixed O|F anion positions, and Rietveld refinements as well as MAPLE calculations support the structure models.

Expanding transition metal borate chemistry to include main group elements: high-pressure synthesis and structural relation of β-MgB4O7

The high-pressure/high-temperature synthesis of β-MgB4O7 at 9 GPa and 1200 °C is presented. The determination of its crystal structure by single-crystal X-ray diffraction has shown that the compound is isotypic to the transition metal borates with the structure type of β-MB4O7 (M = Mn–Zn). β-MgB4O7 crystallizes in the orthorhombic space group Cmcm with the lattice parameters a = 10.848(2), b = 6.513(2), and c = 5.144(1) Å. The structural relation between the normal-pressure phase α-MgB4O7 to the here presented high-pressure phase β-MgB4O7 and to other reference compounds is discussed.

Polymorphism and polymorph-dependent luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2

Building on studies of monoclinic Li₃SiNO₂, a polymorph, β-Li₃SiNO₂, with a previously unknown structure type was synthesized. The β-phase crystallizes in the orthorhombic space group Pbca (no. 61) with lattice parameters of a = 18.736(2), b = 11.1267(5), c = 5.0897(3) Å, and a cell volume of V = 1057.2(1) ų. Using high-temperature solid-state reactions in sealed tantalum tubes, it was possible to obtain high purity samples (<5 wt% of side phase LiSi₂N₃ according to Rietveld analysis) containing exclusively one or the other polymorph, depending solely on the cooling rate. In contrast to the monoclinic phase, orthorhombic β-Li₃SiNO₂ additionally contains a third layer and shows a layer-sequence of the type ABCB. Doped with the activator ion Eu²⁺, the new polymorph exhibits an intense yellow emission (λ_max = 586 nm, fwhm = 89 nm, 0.33 eV, 2650 cm^-1) under irradiation with UV to blue light. Hence, the structural difference between the two polymorphs goes along with a significant blue-shift of 16 nm. The results from single-crystal diffraction and single-grain luminescence measurements were confirmed by Rietveld analysis of bulk samples and powder luminescence data.

Li2 Ba4 Al2 Ta2 N8 O, the First Barium Nitridoalumotantalate with BCT-Zeolite Type Structure

Single-crystals of Li₂ Ba₄ Al₂ Ta₂ N₈ O:Eu²⁺ were synthesized from Ba₃ N₂ , Al₂ O₃ , Li₃ N, Eu₂ O₃ , and lithium metal by a high-temperature solid-state reaction in a weld shut tantalum ampule. The crystal structure of Li₂ Ba₄ Al₂ Ta₂ N₈ O was determined by single-crystal X-ray diffraction and it crystallizes in the orthorhombic space group Pnnm (no. 58) with the lattice parameters a=1006.71(3), b=1026.58(3), c=607.10(2) pm, and a volume of V=0.62742(3) nm³ . The compound is built up from AlN₄ and TaN₄ tetrahedra, which form a three-dimensional network corresponding to the BCT-zeolite type structure. Li₂ Ba₄ Al₂ Ta₂ N₈ O is homeotypic to Li₂ Sr₄ Si₄ N₈ O and Li₂ Sr₄ Al₂ Ta₂ N₈ O but, additionally, it could be successfully doped with the activator ion Eu²⁺ and hence features an experimental observed overall emission at λ_max =565 nm (fwhm=89 nm) consisting of a superposition of two adjusted emission bands at λ_max =557 nm (fwhm=69 nm) and at λ_max =604 nm (fwhm=102 nm).

Ba4Al7Li28.08O26.92N1.08, the Barium Oxonitridolithoaluminate with a Highly Condensed LiO4 Tetrahedra Framework

The new compound Ba₄Al₇Li_28.08O_26.92N_1.08 consists of AlO₄/AlO₃N tetrahedra, 10-fold coordinated Ba²⁺ cations, and a highly condensed edge- and corner-sharing LiO₄ tetrahedra framework, which leads to a degree of condensation greater than 1. The first barium oxonitridolithoaluminate was synthesized by a high-temperature solid-state reaction in a weld-shut tantalum ampoule and the crystal structure has been determined by single-crystal X-ray diffraction. Ba₄Al₇Li_28.08O_26.92N_1.08 crystallizes in the monoclinic space group P2₁/m (no. 11) with the lattice parameters a = 1052.41(3), b = 615.93(2), c = 1088.45(4) pm, β = 98.86(1)°, and a volume of V = 0.69712(4) nm³. In addition, Ba₄Al₇Li_28.08O_26.92N_1.08 doped with the activator ion Eu²⁺, exhibits a broad band emission with a maximum at λ_max = 524 nm (2.34 eV) with a fwhm of 112 nm (4373 cm^-1/0.54 eV), which can be described by a superposition of two adjusted emission bands at λ_max = 515 nm (2.41 eV) with a fwhm of 70 nm (2704 cm^-1/0.34 eV), and at λ_max = 574 nm (2.18 eV) with a fwhm of 127 nm (4127 cm^-1/0.51 eV).

High-pressure synthesis and crystal structure determination of Tb2SiB2O8

We report the high-pressure/high-temperature synthesis (11 GPa, 1300 °C) of the new compound Tb2SiB2O8. This rare earth borosilicate crystallizes in the orthorhombic space group Pbcn (no. 60) with the unit cell parameters a = 13.2480(3), b = 4.3904(1), and c = 9.1611(3) Å. It is built up of corner-sharing [BO4] tetrahedra forming infinite chains, that are connected to layers via [SiO4] tetrahedra. The layers are connected via [TbO7] polyhedra.

Cd[B2(SO4)4] and H2[B2(SO4)4] - a phyllosilicate-analogous borosulfate and its homeotypic heteropolyacid

Borosulfates consist of heteropolyanionic networks of corner-shared (SO₄)- and (BO₄)-tetrahedra charge compensated by metal or non-metal cations. The anionic substructures differ significantly, depending on the different branching of the silicate-analogous borosulfate building blocks. However, only one acid has been characterized by single crystal X-ray diffraction so far. Herein, we present H₂[B₂(SO₄)₄] as the first phyllosilicate analogue representative, together with the homeotypic representative Cd[B₂(SO₄)₄]. The latter can be considered the cadmium salt of the former. Their crystal structures and crystallographic relationship are elucidated. For H₂[B₂(SO₄)₄], the bonding situation is examined using Hirshfeld-surface analysis. Further, the optical and thermal properties of Cd[B₂(SO₄)₄] are investigated by FTIR and UV-Vis spectroscopy, thermogravimetry, as well as temperature-programmed powder X-ray diffraction.

High-pressure synthesis of borate-nitrates: crystal structure of M 3B7O13(NO3) (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+)

The orthorhombic nitrate-boracites with the sum formula M 3B7O13NO3 (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+) were synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 6 GPa and 800 °C, respectively. The crystal structures of the five isotypic substances, which crystallize in the space group Pca21, were determined via single-crystal X-ray diffraction and the structural features of the incorporated nitrate anions are discussed.

Crystal structure determination and characterization of Sm3SiO5F3

In this paper, we present the crystal structure of the novel compound Sm3SiO5F3. Single crystals were obtained using a high-pressure/high-temperature approach. Sm3SiO5F3 crystallizes in the triclinic space group P 1 ‾ $\bar{1}$ (aP24) with a = 6.1894(2), b = 7.1315(2), c = 7.3997(3) Å, α = 103.66(1), β = 98.06(1), γ = 90.16(1)°, V = 314.03(2) Å3, Z = 2 at T = 300 K and, to the best of our knowledge, presents a new structure type. BLBS and CHARDI calculations were used to assign oxidation states to the atoms, thus allowing us to differentiate between fluorine and oxygen atoms within the crystal structure. MAPLE calculations were carried out to support the structure solution. Electron microprobe measurements corroborate the ratio of Sm to Si and unequivocally prove the presence of Si within the compound. Despite various attempts, bulk synthesis of the compound could not be realized.

Fundamental Study of the Optical and Vibrational Properties of Fx-AZB@MOF systems as Functions of Dye Substitution and the Loading Amount

Controlling the switching efficiency of photoactive hybrid systems is an obligatory key prerequisite for systematically improving the design of functional materials. By modulating the degree of fluorination and the amount being embedded into porous hosts, the E/Z ratios of fluorinated azobenzenes were adjusted as both functions of substitution and the degree of loading. Octafluoroazobenzene (F8-AZB) and perfluoroazobenzene (F10-AZB) were inserted into porous DMOF-1. Especially for perfluoroazobenzene (F10-AZB), an immense stabilization of the E isomer was observed. In complementary molecular dynamics simulations performed at the DFTB (density functional tight binding) level, an in-depth characterization of the interactions of the different photoisomers and the host structure was carried out. On the basis of the resulting structural and energetic data, the experimentally observed increase in the amount of the Z conformer for F8-AZB can be explained, while the stabilization of E-F10-AZB can be directly related to a fundamentally different interaction motif compared to its tetra- and octafluorinated counterparts.

The crystal structure and luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2+

Obtained by a high temperature solid-state synthesis, the compound Li3SiNO2:Eu2+ was characterized via SCXRD, PXRD, and luminescence spectroscopy. This revealed a new structure type and interesting luminescence properties.

On the Reduction of MoO3 to MoO2 : A Path to Control the Particle Size and Morphology

During the reduction of molybdenum trioxide (MoO₃) to metallic molybdenum, the first reduction step yielding molybdenum dioxide as an intermediary product is of crucial importance. In this study, we examined the impact of the parameters reduction temperature, water influx, and potassium content on the hydrogen reduction of this first reaction step. Beginning from the same starting material, the chemical vapor transport mechanism was utilized to yield the phase pure MoO₂. Analyses including powder X‐ray diffraction, inductively coupled plasma‐mass spectrometry, scanning electron microscopy, and high performance optical microscopy were performed on the product phases. Modulations of the specific surface areas of molybdenum dioxide ranging from 2.28 to 0.41 m²/g were possible. Furthermore, a distinct shift from small plate‐like grains to cuboid‐like forms was achieved.

Syntheses and Characterization of the Mixed-Valent Manganese(II/III) Fluorides Mn2F5 and Mn3F8

We obtained single crystals of the binary mixed-valent fluorides Mn₂F₅ and Mn₃F₈ using a high-pressure/high-temperature approach. Mn₂F₅ crystallizes isotypic to CaCrF₅ in the monoclinic space group C2/c (No. 15), with a = 8.7078(8) Å, b = 6.1473(6) Å, c = 7.7817(7) Å, β = 117.41(1)°, V = 369.80(6) ų, Z = 4, and mC28 at T = 173 K. Mn₃F₈ crystallizes in the monoclinic space group P2₁ (No. 4) with a = 5.5253(2) Å, b = 4.8786(2) Å, c = 9.9124(4) Å, β = 92.608(2)°, V = 266.92(2) ų, Z = 2, and mP22 at T = 183 K and presents a new structure type. Crystal-chemical reasoning, CHARDI calculations, and quantum-chemical calculations allowed for the assignment of the oxidation states of the Mn atoms. In both bulk compounds, MnF₂ was present as an impurity, as evidenced by powder X-ray diffraction and IR and Raman spectroscopy.

Rb[Li5 Si2 O7 ] - A Latecomer in the Family of Alkali Lithosilicates Hiding a Green-Emitting Lithosilicate

In order to expand the field of alkali lithosilicates, a new representative of the substance class with a previously unknown structure type was found based on solid-state synthesis. The novel compound with the sum formula Rb[Li5 Si2 O7 ] crystallizes in the orthorhombic space group Pbcm (no. 57) with a=7.6269(3), b=9.5415(4), and c=9.4095(3) Å by means of single-crystal X-ray diffraction. The structure consists of a highly condensed lithosilicate framework, built up of corner- and edge-linked [LiO4 ]-tetrahedra and [Si2 O7 ]-units, and the rubidium ions aligned in channels. Suitable crystals of the material were obtained using sealed tantalum ampoules as reaction tube at a temperature of 750 °C. The new compound was further characterized via powder diffraction, Rietveld analysis, and EDX measurements. At first glance, Eu2+ -doped Rb[Li5 Si2 O7 ] reveals an intense green luminescence. In-depth crystal analysis shows that a core-shell formation is present even for apparently high quality single-crystals. As a minority phase, the known green phosphor RbLi[Li3 SiO4 ]2 :Eu2+ is the origin of the luminescence, representing a tiny core inside of the particles surrounded by a large matrix of transparent Rb[Li5 Si2 O7 ] dominating the single-crystal diffraction pattern.

The First High-Pressure Chromium Oxonitridoborate CrB4 O6 N-an Unexpected Link to Nitridosilicate-Chemistry

CrB₄O₆N crystallizes in the non‐centrosymmetric space group P6₃mc (no. 186) with the lattice parameters a=5.1036(1), c=8.3519(3) Å, and a volume of 188.40(1) ų. It was synthesized in a high‐pressure/high‐temperature experiment at 7 GPa and 1673 K and represents the first high‐pressure oxonitridoborate. It is built up of starlike‐shaped entities of four BO₃N tetrahedra, connected via one common nitrogen atom that resembles the fourfold‐coordinated nitrogen atoms in the homeotypic nitridosilicates MYbSi₄N₇ (M=Sr, Ba). Building up a network with channels that contain the Cr³⁺ ions, CrB₄O₆N contains for the first time a tetrahedral building unit in contrast to trigonal planar B(O/N)₃ entities in all other known oxonitridoborates. The structural relations as well as the results of spectroscopic measurements and calculations on the chromium oxonitridoborate are discussed.

Triple-Vertex Linkage of (BO4 )-Tetrahedra in a Borosulfate: Synthesis, Crystal Structure, and Quantum-Chemical Investigation of Sr[B3 O(SO4 )4 (SO4 H)]

Borosulfates are classified as silicate analogue materials. The number of crystallographically characterized compounds is still limited, whereas the structural diversity is already impressive. The anionic substructures of borosulfates exhibit vertex-connected (BO₄ )- and (SO₄ )-tetrahedra, whereas bridging between two (SO₄ )- or even between two (BO₄ )-tetrahedra is scarce. The herein presented compound Sr[B₃ O(SO₄ )₄ (SO₄ H)] is the first borosulfate with a triple-vertex linkage of three (BO₄ ) tetrahedra via one common oxygen atom. DFT calculations complement the experimental studies. Bader charges (calculated for all atoms) as well as charge-density calculations give hint to the electron distribution within the anionic substructure and density-of-states calculations support the interpretation of the bonding situation.

Coexistence of Two Different Distorted Octahedral [MnF6 ]3- Sites in K3 [MnF6 ]: Manifestation in Spectroscopy and Magnetism

As a consequence of the static Jahn‐Teller effect of the ⁵E ground state of Mn^III in cubic structures with octahedral parent geometries, their octahedral coordination spheres become distorted. In the case of six fluorido ligands, [MnF₆]³⁻ anions with two longer and four shorter Mn−F bonds making elongated octahedra are usually observed. Herein, we report the synthesis of the compound K₃[MnF₆] through a high‐temperature approach and its crystallization by a high‐pressure/high‐temperature route. The main structural motifs are two quasi‐isolated, octahedron‐like [MnF₆]³⁻ anions of quite different nature compared to that met in ideal octahedral Mn^III Jahn‐Teller systems. Owing to the internal electric field of C_i symmetry dominated by the next‐neighbour K⁺ ions acting on the Mn^III sites, both sites, the pseudo‐rhombic (site 1) and the pseudo‐tetragonally elongated (site 2) [MnF₆]³⁻ anions are present in K₃[MnF₆]. The compound was characterized by single‐crystal and powder X‐ray diffraction, and magnetometry as well as by FTIR, Raman, and ligand field spectroscopy. A theoretical interpretation of the electronic structure and molecular geometry of the two Mn sites in the lattice is given by using a vibronic coupling model with parameters adjusted from multireference ab‐initio cluster calculations.

Modulating the Optical Characteristics of Spiropyran@Metal-Organic Framework Composites as a Function of Spiropyran Substitution

Understanding the interactions between the single components of hybrid systems is essential to drive the development of advanced functional materials. A prerequisite for this is the systematic variation of the building blocks of such compounds. Focusing on spiropyran@metal-organic framework (MOF) composite materials with noncovalently attached spiropyran dyes, both the host scaffold and the dye molecules can be systematically tuned. In this work, a broad substitution pattern was applied to systematically elucidate the characteristics of the resulting hybrid materials as a function of the supplemental substitution on spiropyran. The newly developed 12 composites exhibit substitution and host-dependent optical characteristics, which are particularly affected by the substitution of the 6'-position on the chromene ring. Through the favorable combination of the MOF host's polarity and an adequate strength of the spiropyran's indoline_donor-chromene_acceptor pair, reversible conversion between photoisomers is efficiently accomplished, especially for nitro-substituted spiropyrans inside MIL-68(In).

Polymorphs of the Gadolinite-Type Borates ZrB2 O5 and HfB2 O5 Under Extreme Pressure

Based on the results from previous high‐pressure experiments on the gadolinite‐type mineral datolite, CaBSiO₄(OH), the behavior of the isostructural borates β‐HfB₂O₅ and β‐ZrB₂O₅ have been studied by synchrotron‐based in situ high‐pressure single‐crystal X‐ray diffraction experiments. On compression to 120 GPa, both borate layer‐structures are preserved. Additionally, at ≈114 GPa, the formation of a second phase can be observed in both compounds. The new high‐pressure modification γ‐ZrB₂O₅ features a rearrangement of the corner‐sharing BO₄ tetrahedra, while still maintaining the four‐ and eight‐membered rings. The new phase γ‐HfB₂O₅ contains ten‐membered rings including the rare structural motif of edge‐sharing BO₄ tetrahedra with exceptionally short B−O and B⋅⋅⋅B distances. For both structures, unusually high coordination numbers are found for the transition metal cations, with ninefold coordinated Hf⁴⁺, and tenfold coordinated Zr⁴⁺, respectively. These findings remarkably show the potential of cold compression as a low‐energy pathway to discover metastable structures that exhibit new coordinations and structural motifs.

Structural, dynamical, and photochemical properties of ortho-tetrafluoroazobenzene inside a flexible MOF under visible light irradiation

Considering porous materials as host matrices is an elegant way to enable photoswitching of non-covalently attached organic dyes even in the solid state. By focusing on the resulting optical properties as a function of loading degree and synthesis procedure, the occurring host-guest and guest-guest interactions can be determined and further exploited. In the course of this study, the photochromic behavior of ortho-tetrafluoroazobenzene (tF-AZB) inside flexible DMOF-1 was investigated from these points of view. It was found that depending on the loading degree and temperature, tF-AZB shows varying E/Z ratios and switching efficiency. For systems with low loading, reversible visible light induced isomerization was observed over ten switching cycles: Upon violet light exposure, formation of 100% E isomer was generated, while green light irradiation resulted in ∼60% Z-tF-AZB. Complementary molecular dynamics simulations at DFTB (density functional tight binding)-level revealed changing binding sites for Z-tF-AZB inside DMOF-1. For the E isomer, only low oscillations have been found, which in turn display a rare T-stacking interaction. Although the interaction strengths of the E and Z isomers with DMOF-1 are in the same range, the different mobility of both isomers due to varying binding sites explains the preference of the E isomer even upon green light exposure.

High-pressure synthesis of REB5O8(OH)2 (RE = Ho, Er, Tm)

The rare earth oxoborates REB5O8(OH)2 (RE = Ho, Er, Tm) were synthesized in a Walker-type multianvil apparatus at a pressure of 2.5 GPa and a temperature of 673 K. Single-crystal X-ray diffraction data provided the basis for the structure solution and refinement. The compounds crystallize in the monoclinic space group C2 (no. 5) and are composed of a layer-like structure containing dreier and sechser rings of corner sharing [BO4]5− tetrahedra. The rare earth metal cations are coordinated between two adjacent sechser rings. Further characterization was performed utilizing IR spectroscopy.

Ni[B2 (SO4 )4 ] and Co[B2 (SO4 )4 ]: Unveiling Systematic Trends in Phyllosilicate Analogue Borosulfates

Borosulfates are compounds analogous to silicates, with heteropolyanionic subunits of vertex-linked (SO₄ )- and (BO₄ )-tetrahedra. In contrast to the immense structural diversity of silicates, the number of borosulfates is yet very limited and the extent of their properties is still unknown. This is particularly true for representatives with phyllosilicate and tectosilicate analogue anionic substructures. Herein, we present Ni[B₂ (SO₄ )₄ ] and Co[B₂ (SO₄ )₄ ], two new borosulfates with phyllosilicate analogue topology. While the anionic subunits of both structures are homeotypic, the positions of the charge compensating cations differ significantly: Ni^II is located between the borosulfate layers, while Co^II -in contrast-is embedded within the layer. Detailed analysis of these two structures based on single-crystal X-ray diffraction, magnetochemical investigations, X-ray photoelectron spectroscopy, and quantum chemical calculations, unveiled the reasons for this finding. By in silico comparison with other divalent borosulfates, we uncovered systematic trends for phyllosilicate analogues leading to the prediction of new species.

High-pressure synthesis and crystal structure of HP-Al2B3O7(OH)

Orthorhombic HP-Al2B3O7(OH) was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 12.4 GPa and 1200 °C, respectively. Its structure is isotypic to that of Ga2B3O7(OH) and has been determined via single-crystal X-ray diffraction at room temperature. HP-Al2B3O7(OH) crystallizes in the space group Cmce (Z = 8) with the lattice parameters a = 10.3124(4), b = 7.3313(3), c = 10.4801(5) Å, and V = 792.33(6) Å3. The compound has also been characterized by IR and Raman spectroscopy.

K2SnOF4 and K2WO3F2 – different but similar

K2SnOF4 and K2WO3F2 were synthesized via a high-pressure/high-temperature route. Single-crystal analysis showed that both substances crystallize in the orthorhombic crystal system with space group Pnma and are isostructural to each other. The main motifs of the structures are octahedral [SnO2F4]4− and [WO4F2]4− entities for K2SnOF4 and K2WO3F2, respectively. Within the structures, these units are connected to quasi-isolated infinite chains. The substances were further characterized via powder X-ray diffraction, EDX and FT-IR spectroscopy. Doping of K2SnOF4 with Mn4+ yielded a red phosphor material which was analyzed by luminescence spectroscopy. The emission maximum is located at λ max = 631 nm.

Al5B12O25(OH) and Ga4InB12O25(OH) – two additional triel borates with the structure type M 5B12O25(OH) (M = Ga, In)

The isotypic triel borates Al5B12O25(OH) and Ga4InB12O25(OH) were synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 12.0 GPa/1400 °C and 12.3 GPa/1200 °C, respectively. The crystal structures of both compounds, determined by single-crystal X-ray diffraction, constitute new representatives of the structure type M 5B12O25(OH) (M = Ga, In) crystallizing in the space group I41/acd. The presence of the hydroxyl groups was confirmed via single-crystal IR spectroscopy.

Syntheses and crystal structures of the manganese hydroxide halides Mn5(OH)6Cl4, Mn5(OH)7I3, and Mn7(OH)10I4

Single-crystals of the new manganese hydroxide halides Mn5(OH)6Cl4, Mn5(OH)7I3, and Mn7(OH)10I4 were obtained by means of high-pressure/high-temperature synthesis in a Walker-type multianvil apparatus. The chloride crystallizes in the monoclinic space group P21/c (no. 14) with the lattice parameters (single-crystal data) a = 592.55(8), b = 1699.7(2), c = 597.33(8) pm, and β = 112.58(1)°. The iodides crystallize in the triclinic space group P 1 ‾ $\bar{1}$ (no. 2) with a = 653.16(2), b = 905.98(3), c = 1242.98(4) pm, α = 114.21(1)°, β = 99.91(1)°, and γ = 94.37(1)° for Mn5(OH)7I3 and a = 656.90(3), b = 906.59(4), c = 909.32(4) pm, α = 119.29(1)°, β = 97.99(1)°, and γ = 95.03(1)° for Mn7(OH)10I4. The crystal structures consist of edge-sharing Mn(OH)6–n X n (X = Cl, I; n = 1, 2, 3) octahedra arranged in stacked sheets. Adjacent layers are connected by hydrogen bonds of type O–H···X, confirmed by further characterization of single-crystals by IR-spectroscopy. The crystal chemical relationship with the aristotype Mg(OH)2 (brucite) is discussed on the basis of Bärnighausen trees (group–subgroup relations).

High-pressure synthesis and characterization of the non-centrosymmetric scandium borate ScB6O9(OH)3

The non-centrosymmetric scandium borate ScB6O9(OH)3 was obtained through a high-pressure/high-temperature experiment at 6 GPa and 1473 K. Single-crystal X-ray diffraction revealed that the structure is isotypic to InB6O9(OH)3 containing borate triple layers separated by scandium layers. The compound crystallizes in the space group Fdd2 with the lattice parameters a = 38.935(4), b = 4.4136(4), and c = 7.6342(6) Å. Powder X-ray diffraction and vibrational spectroscopy were used to further characterize the compound and verify the proposed structure solution.

Borosulfates-Synthesis and Structural Chemistry of Silicate Analogue Compounds

Borosulfates are oxoanionic compounds consisting of condensed sulfur- and boron-centered tetrahedra. Hitherto, they were mostly achieved from solvothermal syntheses in SO3 -enriched sulfuric acid, or from reactions with the superacid H[B(HSO4 )4 ]. The crystal structures are very similar to those of the corresponding class of silicates and their substitution variants, especially regarding the typical structural motif of corner-sharing tetrahedra. However, the borosulfates are supposed to be even more versatile, because (BO3 ) units might also be part of the anionic network. The following article deals with detailed reports on the different synthesis strategies, the crystal chemistry of borosulfates in comparison to silicates, and their hitherto identified properties.