High-pressure synthesis and crystal structure of the mixed-valent titanium borate Ti5B12O26

摘要

The new titanium borate was synthesized under high-pressure/high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1350 degrees C. Ti5B12O26 is built up exclusively from corner-sharing BO4-tetrahedra and shows a structural relation to the Zintl phase NaTl. Consisting Of B12O26-clusters as fundamental building blocks, the structure of Ti5B12O26 can be described via two interpenetrating diamond structures as in NaTl, where each atom corresponds to one B12O26-Cluster. The tetragonal titanium borate crystallizes with eight formula units in the space group 14(1)/acd and exhibits lattice parameters of a = 1121.1(2) pm and c = 2211.5(4) pm. Ti5B12O26 is a mixed-valent compound with Ti-III and Ti-IV cations. The environment of the titanium cations, as well as charge distribution calculations, leads us to the assumption that Ti-III and Ti-IV are located on different crystallographic sites.