Neutron single-crystal refinement of cerussite, PbCO3, and comparison with other aragonite-type carbonates

The crystal structure of cerussite, PbC03, was refined with 669 merged single-crystal neutron data (Fo > 3G(Fo)) to R = 0.032, Rw = 0.Of5 (space group Pmcn;a = 5.179(1),b = 8.492(3),c = 6.141(2);Z = 4). - Cerussite belongs to the aragonite-type compounds. The weak aplanarity of the carbonate group, d = 0.026(1) A, is of the same order of magnitude as in aragonite, CaC03, and strontianite, SrC03, and the direction of the deviation from planarity is the same. The minor details of the stereochemistry differ slightly from the expectations to be drawn from the structures of the alkaline earth carbonates on the basis of the effective ionic radii of the twovalent metals.