Jörn Bruns

ZUSAMMENFASSUNG: Die Reaktion von KReO ₄ mit B ₂ O ₃ in einer Schmelze aus Re ₂ O ₇ führt zu der Bildung eines farblosen, kristallinen Pulvers von K[B(ReO ₄ ) ₄ ]. Die durch Einkristalldiffraktometrie bestimmte Kristallstruktur ist nicht‐zentrosymmetrisch (Raumgruppe I ) und weist das bis dato unbekannte [B(ReO ₄ ) ₄ ] ⁻ ‐Anion auf. Letzteres ist das erste Exemplar eines monomeren Anions mit Bor als Zentralatom, welches über B‐O‐Re‐Bindungen zu vier Perrhenat‐Anionen koordiniert. Die Verbindung wurde zusätzlich via Ramanspektroskopie untersucht und die jeweiligen Schwingungsmodi den beobachteten Banden mittels DFT‐Rechnungen zugeordnet. Des Weiteren konnte durch Frequenzverdopplung (second harmonic generation; SHG) das Fehlen eines Inversionszentrums nachgewiesen werden.

The reaction of KReO ₄ with B ₂ O ₃ in molten Re ₂ O ₇ results in the formation of a colorless crystalline powder of K[B(ReO ₄ ) ₄ ]. The single‐crystal structure determination reveals a non‐centrosymmetric structure (space group I ), containing the hitherto unknown [B(ReO ₄ ) ₄ ] ⁻ anion. This anion presents the first example of a monomeric anion with boron as a central atom coordinated by four perrhenate anions forming B─O─Re bonds. The compound has been further characterized by Raman spectroscopy, with additionally DFT calculations to assign the vibration modes. Moreover, the absence of inversion symmetry has been proven by second harmonic generation (SHG) measurements.

Despite consistent growth in the number of compounds known to host homo‐ and hetero polycations of group 16 elements, only two, Se ₄ [HS ₂ O ₇ ] ₂ and Se ₄ [S ₄ O ₁₃ ], provided an exclusively oxidic coordination environment, the former being the first structural characterization of the Se ₄ ²⁺ cation in 1968. With the first selenium borosulfates Se ₄ [B(S ₂ O ₇ ) ₂ ] ₂ (SO ₃ ), Se ₄ [B(S ₂ O ₇ ) ₂ ] ₂ , Se ₄ [B ₂ (SO ₄ ) ₂ (S ₂ O ₇ ) ₂ ]‐I, Se ₄ [B ₂ (SO ₄ ) ₂ (S ₂ O ₇ ) ₂ ]‐II, and Se ₄ [B ₂ (SO ₄ ) ₄ ] we extended this list by five compounds. Aside from Se ₄ [HS ₂ O ₇ ] ₂ , Se ₄ [S ₄ O ₁₃ ] was synthesized but never structurally characterized. In this contribution we also evaluate the crystal structure of the tetrasulfate Se ₄ [S ₄ O ₁₃ ]. All compounds are synthesized under solvothermal conditions. Powder reflectance spectra of the selenium borosulfates are in accordance with the yellow body color of the compounds. Magnetic measurements confirm the diamagnetic character of the Se ₄ ²⁺ ions, in agreement with the calculations. Temperature‐programmed powder X‐ray diffraction reveals that the borosulfates of the study form sequentially with increasing decomposition temperature, enabling their selective synthesis. Furthermore, we performed infrared spectroscopy, Rietveld refinements and thermal analyses.

Despite consistent growth in the number of compounds known to host homo‐ and hetero polycations of group 16 elements, only two, Se ₄ [HS ₂ O ₇ ] ₂ and Se ₄ [S ₄ O ₁₃ ], provided an exclusively oxidic coordination environment, the former being the first structural characterization of the Se ₄ ²⁺ cation in 1968. With the first selenium borosulfates Se ₄ [B(S ₂ O ₇ ) ₂ ] ₂ (SO ₃ ), Se ₄ [B(S ₂ O ₇ ) ₂ ] ₂ , Se ₄ [B ₂ (SO ₄ ) ₂ (S ₂ O ₇ ) ₂ ]‐I, Se ₄ [B ₂ (SO ₄ ) ₂ (S ₂ O ₇ ) ₂ ]‐II, and Se ₄ [B ₂ (SO ₄ ) ₄ ] we extended this list by five compounds. Aside from Se ₄ [HS ₂ O ₇ ] ₂ , Se ₄ [S ₄ O ₁₃ ] was synthesized but never structurally characterized. In this contribution we also evaluate the crystal structure of the tetrasulfate Se ₄ [S ₄ O ₁₃ ]. All compounds are synthesized under solvothermal conditions. Powder reflectance spectra of the selenium borosulfates are in accordance with the yellow body color of the compounds. Magnetic measurements confirm the diamagnetic character of the Se ₄ ²⁺ ions, in agreement with the calculations. Temperature‐programmed powder X‐ray diffraction reveals that the borosulfates of the study form sequentially with increasing decomposition temperature, enabling their selective synthesis. Furthermore, we performed infrared spectroscopy, Rietveld refinements and thermal analyses.

Syntheses and structural elucidations for the mixed (poly‐)sulfate As ₂ [S ₂ O ₇ ] ₂ [S ₃ O ₁₀ ] ( 1 ) and the two disulfate‐containing pnictogenates [SeCl ₃ ][Pn(S ₂ O ₇ ) ₂ ] (Pn = Sb ( 3 ) and Bi ( 4 )) are reported. As ₂ [S ₂ O ₇ ] ₂ [S ₃ O ₁₀ ] ( C 2/ c , a = 2852.0(2) pm, b = 665.05(3) pm, c = 988.49(4) pm, β = 102.531(2)°, V = 1830.2(1) Å ³ ) is the first example of a mixed condensed polysulfate, showing two [As(S ₂ O ₇ )] units which are bridged by a [S ₃ O ₁₀ ] moiety. For direct structural comparison to the binary sulfate, we redetermined the crystal structure of As ₂ [SO ₄ ] ₃ ( 2 ) at 100 K. The pnictogenates [SeCl ₃ ][Sb(S ₂ O ₇ ) ₂ ] ( P 2 ₁ / c , a = 1197.5(2) pm, b = 1435.2(2) pm, c = 927.6(1) pm, β = 99.362(6)°, V = 1572.9(5) Å ³ ) and [SeCl ₃ ][Bi(S ₂ O ₇ ) ₂ ] ( P 2 ₁ / c , a = 1230.86(7) pm, b = 1343.33(7) pm, c = 930.65(6) pm, β = 98.827(2)°, V = 1520.6(1) Å ³ ) are isotypic. They show complex Pn···O coordination, differing from [M(S ₂ O ₇ ) _n ] ( n = 2, 3, 4) species known from other main group elements. Furthermore, they engage in chalcogen bonding with the [SeCl ₃ ] ⁺ cations. We used quantum chemical calculations (DFT) to get insights on the molecular electrostatic potential surfaces and performed quantum theory of atoms in molecules and natural bond orbital analyses to quantify the strength of the noncovalent interactions.

The reaction of boric acid and methanesulfonic acid yielded single crystals of B ₆ O ₉ ·CH ₃ SO ₃ H (monoclinic, I 2/ a , Z = 8, a = 873.19(3), b = 14.2254(5), c = 1759.33(8) pm, β = 103.433(2)°, and V = 2125.56(1) × 10 ⁶ pm ³ ). The crystal structure exhibits corrugated layers of the central structural motif, which are planar B ₃ O ₃ rings, which are linked to each other via oxygen atoms resulting in a trigonal planar coordination of all boron atoms. Intercalated in these layers are chains of methanesulfonic acid molecules showing medium strong hydrogen bonds. The compound has also been analyzed via thermal gravimetry, IR and Raman spectroscopy. ¹ H, ¹¹ B, and ¹³ C solid‐state NMR analyses corroborate the structural findings and are in good agreement with expected values.

The solvothermal reaction of RbCl, boric acid, and chlorosulfuric acid yielded Rb[B(SO ₄ ) ₂ ]. The crystal structure of Rb[B(SO ₄ ) ₂ ] (tetragonal, P 4/ ncc, Z = 4, a = 9.1823(3) Å, c = 7.4559(5) Å, V = 628.64(6) Å) is isotypical to the previously published borosulfates A [B(SO ₄ ) ₂ ] ( A = K , Ag) and exhibits 1D anionic chains of vertex‐connected (SO ₄ )‐ and (BO ₄ )‐tetrahedra. The product has been obtained phase pure according to powder X‐ray diffraction and subsequent Rietveld refinement.

Subvalent silver oxides, where silver exhibits an oxidation state between 0 and + 1, have traditionally been discovered serendipitously due to a lack of systematic synthesis methods and understanding of their bonding schemes. This study presents a novel, purposeful approach to synthesizing multinary subvalent silver oxides through high‐pressure techniques. By subjecting the monovalent silver oxide Ag ₂ PdO ₂ to hydrostatic pressure of ∼30 GPa and laser heating at 1500 K, subvalent Ag ₅ Pd ₂ O ₄ forms besides PdO. The crystal structure of Ag ₅ Pd ₂ O ₄ , determined via in situ single‐crystal X‐ray diffraction, reveals distinct layers of cationic silver aggregates and anionic oxopalladate units. Electronic structure calculations confirm the subvalent nature of silver in Ag ₅ Pd ₂ O ₄ , showing a vanished band gap and increased electron density on silver atoms. The findings pave the way for developing materials with rich magneto‐electronic functionalities, owing to the interplay between subvalent silver and transition metal cations.

The reaction of elemental palladium with B ₂ O ₃ and SO ₃ at elevated temperature results in the formation of blue crystals of Pd[B(S ₂ O ₇ ) ₂ ] ₂ . Dependent on the reaction conditions, the compound crystallizes in two different polymorphs obtained as bulk samples. In both structures the Pd ²⁺ cations are coordinated by six oxygen atoms in form of an almost perfect octahedron. All oxygen atoms belong to the borosulfate anions [B(S ₂ O ₇ ) ₂ ] ⁻ and link via Pd ²⁺ cations to an extended network structure. Within the uncommon octahedral oxygen coordination, the Pd ²⁺ cations reveal a d ⁸ high‐spin configuration, which leads to paramagnetism. Occasionally, red crystals are formed during the reaction next to the major fraction of blue crystals of Pd[B(S ₂ O ₇ ) ₂ ] ₂ . Single crystal X‐ray structure analysis on the red crystals reveals the sum formula Pd[B(SO ₄ )(S ₂ O ₇ )] ₂ with Pd ²⁺ in square‐planar coordination.