Li2B6O9F2, a New Acentric Fluorooxoborate

Abstract Novel Li 2 B 6 O 9 F 2 can be either synthesized from LiBF 4 and B 2 O 3 or from LiB 3 O 5 and LiBF 4 , at 673 K. The three dimensional anionic network is related to the polymeric anion of pentaborates M B 5 O 8 ( M : Rb, Cs); replacing one bridging oxygen atom per repetition unit of the latter by BF 2 O 2 tetrahedron yields the again three dimensional fluorooxoborate anion of the title compound.The new solid electrolyte is stable up to 753 K and decomposes evolving BF 3 . It is a purely ionic conductor with conductivities of 1.3 × 10 –8 and 2.2 × 10 –10 S · cm –1 at 573 and 473 K, respectively.