Mg₅TiO₄(BO₃)₂

Abstract

Single crystals of pentamagnesium titanium(IV) tetraoxide bis(borate), Mg(5)TiO(4)(BO(3))(2), were prepared by slow cooling of the melt from 1623 K in air. The crystal is isostructural with the mineral ludwigite (Mg(2)FeO(2)BO(3)). The Mg and Ti atoms are coordinated by six O atoms and the B atom is coordinated by three O atoms. There are three Mg sites and one mixed site statistically occupied by Mg and Ti atoms. Atoms are at the following special positions: 2a (0, 0, 0) and 2d (0, 1/2, 1/2) for two Mg atoms, 4g (x, y, 0) for the mixed Ti/Mg site and the BO(3) group, and 4h (x, y, 1/2) for a third Mg and two oxide O atoms. MgO(6) and (Ti/Mg)O(6) octahedra are connected by sharing of edges to form zigzag folding layers along the c axis. Triangular prismatic tunnels are formed between the folding layers by sharing apical O atoms of the MgO(6) and (Ti/Mg)O(6) octahedra.