Crystal Structures of the New Borate Fluorides BaMBO3F2 (M=Ga, Al)

Two new borate fluorides, BaMBO3F2 (M=Ga, Al), have been synthesized by hydrothermal and solid-state reactions. The structure of BaGaBO3F2 has been determined by single-crystal X-ray diffraction (P63/m, a=4.907(2) ?, c=9.620(5) ?, Z=2, wR(F2)=0.039 for 334 unique reflections). BaAlBO3F2 has been confirmed to be isostructural by Rietveld refinement of powder X-ray data (a=4.882(1) ?, c=9.398(1) ?, Z=2, Rwp=0.222, CHI3=2.59). The BaMBO3F2 structure-type is built of (001) layers of corner-sharing MO3F2 triangular bipyramids and BO3 triangles, with the Ba atoms filling 12-coordinated interlayer sites.