Single crystal X-ray study of rhombohedral cobaltfluorine (OH) boracite

Co3B7O13F(OH), space group R3c, arh =12.0738(6) Å, αrh = 89.59(5), Z=6, residual R=0.059 (1970 reflections, 78 parameters). In contrast to cubic boracites the structure contains strong metal-halogen bonds (d(Co—F)=2.169(3) Å). Some of the oxygen-boron bonds are considerably weakened