The Indium Borate In19B34O74(OH)11 with T2 Supertetrahedra

Magnesium cations as templates for the self-assembly of supramolecular luminescent {Mg@[B18φ34-35]}-clusters

Solvothermal reaction of magnesium nitrate and boron oxide in N,N-dimethylformamide produced a number of particularly complex supramolecular magnesium borates. Five topologically different types of negatively charged {Mg@[B18φ34-35]}-clusters, φ = O, OH, were observed with the magnesium cation as a core and octadecaborate anions as shells. The clusters assemble via common borate polyhedra forming 1D chains, a 2D mesoporous layer, and 3D mesoporous frameworks with an effective channel width of up to 16 Å. Topological analysis of the clusters in combination with the modular crystallography approach indicates that numerous new functional materials can be obtained by varying their assembly mode. At least one compound containing such clusters exhibits a very strong luminescence.

A Mini Review on Borate Photocatalysts for Water Decomposition: Synthesis, Structure, and Further Challenges

The development of novel photocatalysts, both visible and UV-responsive, for water decomposition reactions is of great importance. Here we focused on the application of the borates as photocatalysts in water decomposition reactions, including water splitting reaction, hydrogen evolution half-reaction, and oxygen evolution half-reaction. In addition, the rates of photocatalytic hydrogen evolution and oxygen evolution by these borate photocatalysts in different water decomposition reactions were summarized. Further, the review summarized the synthetic chemistry and structural features of existing borate photocatalysts for water decomposition reactions. Synthetic chemistry mainly includes high-temperature solid-state method, sol-gel method, precipitation method, hydrothermal method, boric acid flux method, and high-pressure method. Next, we summarized the crystal structures of the borate photocatalysts, with a particular focus on the form of the B-O unit and metal-oxygen polyhedral in the borates, and used this to classify borate photocatalysts, which are rarely mentioned in the current photocatalysis literature. Finally, we analyzed the relationship between the structural features of the borate photocatalysts and photocatalytic performance to discuss the further challenges faced by the borate photocatalysts for water decomposition reactions.

Supertetrahedral anions in the phosphidosilicates Na1.25Ba0.875Si3P5 and Na31Ba5Si52P83

Solid ionic conductors are one key component of all-solid-state batteries, and recent studies with lithium, sodium and potassium phosphidosilicates revealed remarkable ion conduction capabilities in these compounds. We report the synthesis and crystal structures of two quaternary phosphidosilicates with sodium and barium, which crystallize in new structure types. Na1.25Ba0.875Si3P5 contains layers of T3 supertetrahedra, while Na31Ba5Si52P83 forms defect T5 entities and contains Si-Si bonds and P3 trimers. Though T1-relaxometry data indicate a relatively low activation energy for Na+ migration of 0.16 eV, the crystal structures lack sufficient three-dimensional migration paths necessary for fast sodium ion conductvity.

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.

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.

A Series of Chalcogenide Borates RE6Ta2MgQB8O26 (RE = Sm, Eu, Gd; Q = S, Se) Featuring a B4O10 Cluster

New compounds with multiple anions are receiving increasing interest in view of their diverse structures and physical properties. Here we report four isostructural hexanary RE₆Ta₂MgQB₈O₂₆ (RE = Sm, Eu, Gd; Q = S, Se), belonging to the rare chalcogenide borates. Their structures feature an unprecedented [B₄O₁₀]^8- unit comprised of one BO₄ and three BO₃ units. Their 3D structures are constructed by the connection between QRE₆ octahedra and the _∞{[Mg(TaB₄O₁₃)₂]^16-} polyanionic layer. Density functional theory calculations on the electronic structure and a birefringence of 4 are also performed.

Uncommon structural and bonding properties in Ag16B4O10

Ag₁₆B₄O₁₀ has been obtained as a coarse crystalline material via hydrothermal synthesis, and was characterized by X-ray single crystal and powder diffraction, conductivity and magnetic susceptibility measurements, as well as by DFT based theoretical analyses. Neither composition nor crystal structure nor valence electron counts can be fully rationalized by applying known bonding schemes. While the rare cage anion (B₄O₁₀)⁸⁻ is electron precise, and reflects standard bonding properties, the silver ion substructure necessarily has to accommodate eight excess electrons per formula unit, (Ag⁺)₁₆(B³⁺)₄(O²⁻)₁₀ × 8e⁻, rendering the compound sub-valent with respect to silver. However, the phenomena commonly associated with sub-valence metal (partial) structures are not perceptible in this case. Experimentally, the compound has been found to be semiconducting and diamagnetic, ruling out the presence of itinerant electrons; hence the excess electrons have to localize pairwise. However, no pairwise contractions of silver atoms are realized in the structure, thus excluding formation of 2e–2c bonds. Rather, cluster-like aggregates of an approximately tetrahedral shape exist where the Ag–Ag separations are significantly smaller than in elemental silver. The number of these subunits per formula is four, thus matching the required number of sites for pairwise nesting of eight excess electrons. This scenario has been corroborated by computational analyses of the densities of states and electron localization function (ELF), which clearly indicate the presence of an attractor within the shrunken tetrahedral voids in the silver substructure. However, one bonding electron pair of s and p type skeleton electrons per cluster unit is extremely low, and the significant propensity to form and the thermal stability of the title compound suggest d¹⁰–d¹⁰ bonding interactions to strengthen the inter-cluster bonding in a synergistic fashion. With the present state of knowledge, such a particular bonding pattern appears to be a singular feature of the oxide chemistry of silver; however, as indicated by analogous findings in related silver oxides, it is evolving as a general one.

Ag₁₆B₄O₁₀, obtained via hydrothermal synthesis, displays an unprecedented bonding scheme, hosting excess electrons localized pairwise in cluster-like silver subunits.

The novel borate Lu5Ba6B9O27 with a new structure type: synthesis, disordered crystal structure and negative linear thermal expansion

Single crystals of Lu₅Ba₆B₉O₂₇ were obtained by cooling from a melt and polycrystals of the borate were prepared using a multi-step solid-state synthesis. The crystal structure was determined from single-crystal X-ray diffraction data. The borate crystallizes in a new structure type in the monoclinic crystal system in space group C2/c, with cell parameters a = 13.0927 (3), b = 9.9970 (2) and c = 20.4884 (4) Å, β = 106.827 (1)°, V = 2566.86 (9) ų and Z = 4. It is described as a framework composed of rings consisting of vertex-sharing [BO₃] triangles and [LuO₆] octahedra. The Ba atoms are in the cavities of the framework. The structure is disordered: one of the B atoms is surrounded by six O atoms with partial occupancies of 0.5. The thermal properties of Lu₅Ba₆B₉O₂₇ were investigated by thermal analysis and high-temperature X-ray powder diffraction. Its thermal expansion is highly anisotropic. The negative expansion (contraction) is along the b axis, i.e. parallel to the planes of the largest number of [BO₃] triangles. The coefficient of negative linear expansion ranges from -1.42 (at 20°C) to -5.57 × 10^-6 °C^-1 (at 1000°C). Thermal deformation of the ac plane is described in terms of the theory of shear deformation of monoclinic crystals. The Lu₅Ba₆B₉O₂₇ sample melts at 1170°C.

High-pressure synthesis and crystal structure of the mixed-cation borate Ga4In4B15O33(OH)3

The mixed cation triel borate Ga4In4B15O33(OH)3 was synthesized in a Walker-type multianvil apparatus at high-pressure/high-temperature conditions of 12.5 GPa and 1300°C. Although the product could not be reproduced in further experiments, its crystal structure could be reliably determined via single-crystal X-ray diffraction data. Ga4In4B15O33(OH)3 crystallizes in the tetragonal space group I41/a (origin choice 2) with the lattice parameters a = 11.382(2), c = 15.244(2) Å, and V = 1974.9(4) Å3. The structure of the quaternary triel borate consists of a complex network of BO4 tetrahedra, edge-sharing InO6 octahedra in dinuclear units, and very dense edge-sharing GaO6 octahedra in tetranuclear units.

Li2Na2[B12O19(OH)2]: a new open framework borate with a pcu-type net constructed from large cyclic dodeca-oxoboron units

A new open-framework borate with a pcu-type net has been made under solvothermal conditions by incorporating large cyclic dodeca-oxoboron clusters.

(NH4)InB8O14 – a high-pressure borate combining BO3 groups with corner- and edge-sharing BO4 tetrahedra

The first ammonium indium borate (NH4)InB8O14 was synthesized from indium oxide and boric acid under high-pressure/high-temperature conditions of 9 GPa and 1000°C with a Walker-type multianvil apparatus in a BN crucible. Although a reproduction of this synthesis product failed until now, we were able to determine the crystal structure via single-crystal X-ray diffraction data collected at room temperature. (NH4)InB8O14 crystallizes in the monoclinic space group P2/m (Z=2) with a=4.4053(2), b=7.8184(3), c=12.4685(4) Å, β=94.60(1)°, and V=428.06(3) Å3. The structure comprises all three basic structural units of borates, namely corner-sharing BO4 tetrahedra, edge-sharing BO4 tetrahedra, and planar BO3 groups. Large cavities in the borate network give space to disordered, isolated ammonium ions. The presence of nitrogen (confirmed by EDX analysis) appears to originate from the container material.

Exploration into the Syntheses of Gallium- and Indiumborates under Extreme Conditions: M5 B12 O25 (OH): Structure, Luminescence, and Surprising Photocatalytic Properties

Explorative solid-state chemistry led to the discovery of the two new compounds Ga₅ B₁₂ O₂₅ (OH) and In₅ B₁₂ O₂₅ (OH). Extreme synthetic conditions within the range of 12 GPa and a temperature of 1450 °C realized in a Walker-type multianvil apparatus resulted in the formation of an unprecedented tetragonal structure with the exclusive presence of condensed BO₄ tetrahedra, forming cuboctahedral cavities. Doping of these cavities with Eu³⁺ in In₅ B₁₂ O₂₅ (OH) yielded in an orange-red luminescence. Photocatalytic tests of In₅ B₁₂ O₂₅ (OH) revealed a hydrogen production rate comparable to TiO₂ but completely co-catalyst free.

Hydrothermal synthesis and characterization of the praseodymium borate-nitrate Pr[B5O8(OH)(H2O)0.87]NO3·2H2O

The praseodymium borate-nitrate Pr[B5O8(OH)(H2O)0.87]NO3·2H2O was obtained in a hydrothermal synthesis. It crystallizes monoclinically in the space group P21/n (no. 14) with four formula units (Z=4) and unit cell parameters of a=641.9(3), b=1551.8(7), c=1068.4(5) pm, with β=90.54(2)° yielding V=1.0643(8) nm3. The defect variant constitutes the missing member in the series of isostructural, early rare earth borate-nitrates of the composition RE[B5O8(OH)(H2O) x ]NO3·2H2O [RE=La (x=0; 1), Ce (x=1), Nd (x=0.85), Sm (x=0)]. In addition to powder and single-crystal X-ray diffraction data, the novel borate-nitrate was characterized through IR and Raman spectroscopy.

A novel supramolecular magnesoborate framework with snowflake-like channels built by unprecedented huge B69 cluster cages

A novel magnesoborate with a 3D supramolecular framework has been made under solvothermal conditions, showing wonderful snowflake-like motif channels assembled from unprecedented B₆₉ cluster cage units.