The crystal structure of a complex barium,aluminium, copper(II) fluoride: Ba4Cu2Al3F21

Ba₄Cu₂Al₃F₂₁ is orthorhombic : a = 5.299(1) Å, b = 7.318(1) Å, c = 41.529(7) Å, Z = 4. The crystal structure was solved in the space group P2₁2₁2₁ (n^o19) from X-ray single crystal data using 5682 unique reflections (3698 with F_O/σ(F) > 4). It consists in a succession along c of 8 layers of 2 different types of sheets. The first layer, formulated Cu₂AlF₁₁]⁴⁻ in which copper-fluorine octahedra are linked by edges to form infinite distorted chains connected together by aluminium-fluorine octahedra, is followed by two Al₂F₁₀]⁴⁻ layers of infinite cischains of aluminium-fluorine octahedra linked by two vertices and another Cu₂AlF₁₁]⁴⁻ layer. These 4 layers are doubled along c by one of the screw-axes 2₁. The barium ions, 12-coordinated, are inserted between the sheets.