Hubert Huppertz

Five transition metal borates were synthesized in a Walker-type module under high-pressure/high-temperature conditions of 8–9 GPa and 800–1200 °C. They all exhibit the same interpenetrating, anionic borate network B 12 O 26 16− , crystallizing in the space group I 4 1 / acd , and therefore show high similarities to the borates Ti 5 B 12 O 26 and Ga 5 B 12 O 25 (OH). Cr 5 B 12 O 25 (OH) and V 5 B 12 O 25 (OH) are isotypic to Ga 5 B 12 O 25 (OH), whereas Mn 5 Mn 0.83 B 12 O 26 and Fe 5 Fe 0.14 B 12 O 24.3 (OH) 1.7 feature the partial occupation of an additional, cuboctahedral cavity in the structure. This is due to a partial reduction of the cations to the oxidation state +2, as presented with the novel compound Mn 5 MnB 12 O 22 (OH) 4 , which only features Mn 2+ for charge compensation. These structures feature a twelvefold coordination of manganese and iron.