Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The isotypic trielborates <jats:italic>c</jats:italic>‐Al<jats:sub>5</jats:sub>B<jats:sub>12</jats:sub>O<jats:sub>25</jats:sub>(OH), <jats:italic>c</jats:italic>‐Al<jats:sub>1.7</jats:sub>Ga<jats:sub>3.3</jats:sub>B<jats:sub>12</jats:sub>O<jats:sub>25</jats:sub>(OH), and <jats:italic>c</jats:italic>‐Ga<jats:sub>4</jats:sub>InB<jats:sub>12</jats:sub>O<jats:sub>25</jats:sub>(OH) were synthesized under high‐pressure/high‐temperature conditions of ≥12 GPa and ≥1100 °C. The three cubic compounds crystallize in the space group <jats:italic>Fm</jats:italic><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/ejic202001136-math-0001.png" xlink:title="urn:x-wiley:14341948:media:ejic202001136:ejic202001136-math-0001" />
<jats:italic>m</jats:italic> with <jats:italic>Z</jats:italic>=4 and <jats:italic>a</jats:italic>=10.8226(5), 10.9258(5), and 11.176(2) Å for <jats:italic>c</jats:italic>‐Al<jats:sub>5</jats:sub>B<jats:sub>12</jats:sub>O<jats:sub>25</jats:sub>(OH), <jats:italic>c</jats:italic>‐Al<jats:sub>1.7</jats:sub>Ga<jats:sub>3.3</jats:sub>B<jats:sub>12</jats:sub>O<jats:sub>25</jats:sub>(OH), and <jats:italic>c</jats:italic>‐Ga<jats:sub>4</jats:sub>InB<jats:sub>12</jats:sub>O<jats:sub>25</jats:sub>(OH), respectively. The crystal structures of all three compounds were determined by single‐crystal X‐ray diffraction revealing disordered cubic structures composed of <jats:italic>M</jats:italic>O<jats:sub>6</jats:sub> octahedra (<jats:italic>M</jats:italic>=Al, Al/Ga, Ga, In) and BO<jats:sub>4</jats:sub> tetrahedra. Single‐crystal Raman and IR spectroscopic data further characterize the compounds, and the latter confirms the presence of hydroxyl groups.</jats:p>