Abstract
The bismuth-rich subbromide Bi39Pb9Br47 = (Bi95+)4[Bi3Pb9Br47]20– was crystallized from a melt of bismuth, lead, and BiBr3. X-ray diffraction on several crystals revealed a (predominantly) monoclinic structure (space group C2/m, no. 12) with lattice parameters a = 18.832(1) Å, b = 18.961(1) Å, c = 36.355(2) Å and β = 97.51(1)°. The unit cell, which contains C4v-symmetric Bi95+ polycations and a complex bromido-plumbate(II)-bismuthate(III) framework, can be interpreted as one layer, which for the most part follows the tetragonal layer symmetry p4/mbm. The stacking of the layers along [001] lowers the symmetry of the structure. The high pseudosymmetry causes local disorder as well as twinning with partial pseudo-coincidence along the tetragonal c-axis. Due to small domain sizes diffuse scattering occurs. Weak maxima on the diffuse streaks can be assigned to an emergäing superstructure with a period of two layers and orthoärhombic symmetry, which corresponds to a repetitive polysynthetic twin with domain size of one unit cell only.
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