Preparation and crystal structure of a new bismuth chromate: Bi8(CrO4)O11

Single crystals of a new bismuth chromate, Bi₈(CrO₄)O₁₁, were prepared by hydrothermal reaction of NaBiO₃·nH₂O in K₂CrO₄ solution. The bismuth chromate crystallizes in the monoclinic space group P2₁/m with a=9.657(3), b=11.934(3), c=13.868(2)Å and β=104.14(1)°, Z=4 and the final R factors are R=0.038 and R_w=0.041 for 3541 unique reflections. The crystal structure has a slab built up by (CrO₄)²⁻ tetrahedra and distorted bismuth polyhedra which are five-fold pyramids, six-fold trigonal prisms and octahedra. The distance of lone pair from nucleus for bismuth atoms ranges from 0.29 to 1.12 Å, depending on the coordination environment. Bi₈(CrO₄)O₁₁ decomposes to Bi₁₄CrO₂₄ and a small amount of an unknown phase at 796 °C.