HP‐CsB₅O₈: Synthesis and Characterization of an Outstanding Borate Exhibiting the Simultaneous Linkage of All Structural Units of Borates

Abstract

The new cesium pentaborate HP-CsB5 O8 is synthesized under high-pressure/high-temperature conditions of 6 GPa and 900 °C in a Walker-type multianvil apparatus. The compound crystallizes in the orthorhombic space group Pnma (Z=4) with the parameters a=789.7(1), b=961.2(1), c=836.3(1) pm, V=0.6348(1) nm(3) , R1 =0.0359 and wR2 =0.0440 (all data). The new structure type of HP-CsB5 O8 exhibits the simultaneous linkage of trigonal BO3 groups, corner-sharing BO4 tetrahedra, and edge-sharing BO4 tetrahedra including the presence of threefold-coordinated oxygen atoms. With respect to the rich structural chemistry of borates, HP-CsB5 O8 is the second structure type possessing this outstanding combination of the main structural units of borates in one compound. The structure consists of corrugated chains of corner- and edge-sharing BO4 tetrahedra interconnected through BO3 groups forming octagonal channels. Inside these channels, cesium is 13+3-fold coordinated by oxygen atoms. (11) B MQMAS NMR spectra are analyzed to estimate the isotropic chemical shift values and quadrupolar parameters. IR and Raman spectra are obtained and compared to the calculated vibrational frequencies at the Γ-point. The high-temperature behavior is examined by means of temperature-programmed powder diffraction.

La3B6O13(OH): The First Acentric High‐Pressure Borate Displaying Edge‐Sharing BO4 Tetrahedra

“…For the characterization and validation of the edge‐sharing BO 4 tetrahedra in Dy 4 B 6 O 15 , Raman spectroscopy is an eligible method because it features two sharp bands for the B 2 O 6 group in the range between ≈1200 and 1450 cm −1 , that is, at positions where normally no signals appear in this substance class. Calculations made for HP‐CsB 5 O 9 confirmed the assignment of these vibrational bands to the edge‐sharing BO 4 tetrahedra . Furthermore, the possible existence of this structural feature in borate and borosilicate glasses is of great interest in the glass community and makes characterization by solid‐state NMR spectroscopy inevitable.…”

“…The B⋅⋅⋅B distance inside the edge‐sharing tetrahedra of La 3 B 6 O 13 (OH) is 2.077 Å and, therefore, corresponds well with the values in already known high‐pressure borates such as Dy 4 B 6 O 15 (2.072 Å), α‐Gd 2 B 4 O 9 (2.04 Å), and HP‐NiB 2 O 4 (2.088 Å) . Higher B⋅⋅⋅B distances were found, for example, in HP‐KB 3 O 5 (2.21 Å) and HP‐CsB 5 O 8 (2.17 Å), where the oxygen atoms forming the common edge are coordinated by a third boron atom and not a metal cation, as in the aforementioned compounds with smaller B⋅⋅⋅B distances. All B−O distances and O‐B‐O angles can be gathered from Table and Table .…”

“…Since then, several other borates containing edge‐sharing BO 4 tetrahedra have been discovered under high‐pressure, like α‐ RE 2 B 4 O 9 ( RE =Y, Sm‐Ho), HP‐ M B 2 O 4 ( M =Fe, Co, Ni), HP‐KB 3 O 5 , and HP‐CsB 5 O 8 , and also under ambient and hydrothermal conditions, like in KZnB 3 O 6 , Li 4 Na 2 CsB 7 O 14 , β‐CsB 9 O 14 , and α‐Ba 3 [B 10 O 17 (OH) 2 ] …”

The UV-phosphor strontium fluorooxoborate Sr[B5O7F3]:Eu

“…A B-O [3] bond is presumably weaker than a B-O [2] bond causing a shift to smaller wavenumbers from the standard regime. The presence of an infrared band in this range in other borates featuring three-fold-coordinated oxygen [10,[20][21][22] supports our tentative assignment. A respective asymmetric mode is to be expected at lower frequencies, maybe the sharp vibration around 720 cm −1 might fit -but this is rather speculative as the spectrum is very busy in this regime.…”

High‐Pressure Synthesis and Crystal Structure of the Highly Condensed Yttrium Borate YB7O12

“…Since the beginning of our investigations of high‐pressure borates, one of our main goals was the synthesis of anionic backbones as highly condensed as possible. Previous attempts of our group to accomplish that, led to the discovery of various high‐pressure borates with highly connected boron‐oxygen frameworks, for example CsB 5 O 8 , HP‐ M B 3 O 5 , ( M = K, Rb, Tl), HP‐Cs 1– x (H 3 O) x B 3 O 5 ( x = 0.5–0.7), and HP‐(NH 4 )B 3 O 5 , all of them containing simultaneously planar BO 3 groups as well as edge‐ and corner‐sharing BO 4 tetrahedra. The presence of these different structural groups and connections between them enriched by threefold‐coordinated oxygen atoms makes it difficult to find a quantitative parameter for the comparison of these borates with respect to a degree of condensation expressed by the ratio B/O.…”