Oxonium Ions Substituting Cesium Ions in the Structure of the New High‐Pressure Borate HP‐Cs_1−x(H₃O)_xB₃O₅ (x=0.5–0.7)

Abstract

The new high-pressure borate HP-Cs1-x (H3 O)x B3 O5 (x=0.5-0.7) was synthesized under high-pressure/high-temperature conditions of 6 GPa/900 °C in a Walker-type multianvil apparatus. The compound crystallizes in the monoclinic space group C2/c (Z=8) with the parameters a=1000.6(2), b=887.8(2), c=926.3(2) pm, β=103.1(1)°, V=0.8016(3) nm(3) , R1=0.0452, and wR2=0.0721 (all data). The boron-oxygen network is analogous to those of the compounds HP-MB3 O5 , (M=K, Rb) and exhibits all three structural motifs of borates-BO3 groups, corner-sharing BO4 tetrahedra, and edge-sharing BO4 tetrahedra-at the same time. Channels inside the boron-oxygen framework contain the cesium and oxonium ions, which are disordered on a specific site. Estimating the amount of hydrogen by solid-state NMR spectroscopy and X-ray diffraction led to the composition HP-Cs1-x (H3 O)x B3 O5 (x=0.5-0.7), which implies a nonzero phase width.

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

“…This leads to rather long BÀO distances to the oxygen atoms O1 and O4 at the common edge (154.1(2) and 152.9(2) pm, respectively), whereas the BÀO distances to the oxygen atoms at the remaining corners (O2 and O5) are shortened to 141.4(2) and 142.8(2) pm, respectively. The value of the O-B-O bond angle between the oxygen atoms at the common edge and the central boron atom is This kind of distortion is typical for tetrahedra forming B 2 O 6 groups, and is even stronger in the structure type of HP-KB 3 O 5 with the four phases HP-MB 3 O 5 (M = K, Rb, Tl) and HP-Cs 1Àx -(H 3 O) x B 3 O 5 (x = 0.5-0.7) [7] (see Table 6). A graphical comparison of the distances and angles inside the B 2 O 6 units of all known compounds with edgesharing BO 4 tetrahedra is shown in Figures 5 and 6.…”

“…The access to a high-pressure device using the multianvil technique [1] enabled us to synthesize the new high-pressure alkali metal borates HP-LiB 3 O 5 , [2] HP-Na 2 B 4 O 7 , [3] HP-KB 3 O 5 , [4] HP-RbB 3 O 5 , [5] HP-TlB 3 O 5 , [6] and HP-Cs 1Àx (H 3 O) x B 3 O 5 (x = 0.5-0.7). [7] Several interesting structural motifs in these phases, which had not been observed so far, emphasize the high-pressure route as a useful tool for establishing new structure types. For example, the structure of HP-LiB 3 O 5 is built up of layers of BO 4 tetrahedra linked by threefold-coordinated oxygen atoms (O [3] ), which are preferred in high-pressure borates.…”

“…HP-Cs 1Àx (H 3 O) x B 3 O 5 (x = 0.5-0.7) is a substitutional variant of HP-MB 3 O 5 (M = K, Rb, Tl); however, a large proportion of the cesium cations are replaced by oxonium ions. [7] This is because the diameter of the cesium ion exceeds the distance between two neighboring sites, so full occupation of the specific sites would lead to the overlap of two cesium ions; this is prevented by the partial substitution of Cs + with oxonium ions. Interestingly, this was the first time that oxonium ions had been found in a borate structure.…”

“…Interatomic distances [pm] of HP-CsB 5 O 8 compared to HP-MB 3 O 5 (M = K, Rb, Tl)[4][5][6] and HP-Cs 0.4 (H 3 O) 0.6 B 3 O 5[7] (standard deviations in parentheses).HP-CsB5 O 8 HP-KB 3 O 5 HP-RbB 3 O 5 HP-Cs 0.4 (H 3 O) 0.…”

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.…”