Li3Ba4Sc3(BO3)4(B2O5)2: featuring the coexistence of isolated BO3 and B2O5 units

Abstract

A new mixed alkali/alkaline earth scandium borate with the composition Li₃Ba₄Sc₃B₈O₂₂, has been obtained using a high-temperature flux method. Its structure contains two types of isolated and almost co-planar BO₃ and B₂O₅ groups and can be described as Li₃Ba₄Sc₃(BO₃)₄(B₂O₅)₂. Sc atoms connect the oxygen atoms belonging to the BO₃ or B₂O₅ groups in the form of six-coordinated octahedron ScO₆ to compose a unique ²_∞[Sc₃B₈O₂₂] double-layer with the Li and Ba atoms filling in the space among the double layers. Although many kinds of B–O groups have been found in borates, two types of isolated B–O groups coexisting in a single compound is uncommon as it directly violates the Pauling rule of parsimony.