Investigation of the crystal structure of a basic bismuth(III) nitrate with the composition [Bi6O4(OH)4](0.54(1))[Bi6O5(OH)3](0.46(1))(NO3)(5.54(1)).

A basic bismuth(III) nitrate with the composition [Bi(6)O(4)(OH)(4)](0.5)[Bi(6)O(5)(OH)(3)](0.5)(NO(3))(5.5) formed in a slow crystal growth mode has an ordered crystal structure with the monoclinic space group P2(1) and lattice parameters a = 15.850(3), b = 14.986(3), c = 18.230(4) Å, β = 107.329(17)° and volume V = 4133.6 Å(3) (Henry et al. 2003). In a very fast crystal growth mode the complex ions disorder in another P2(1) cell with slightly different lattice parameters a = 15.8404(1), b = 15.1982(1), c = 18.3122(1) Å, β = 106.829(1)° and V = 4219.8 Å(3). This cell can be related to two smaller cells: a monoclinic C2/m cell with a = 13.7161(1), b = 15.1943(1), c = 10.2399(1) Å, β = 98.586(1)° and V = 2110.1 Å(3) and a trigonal R3 cell with a = 15.18650(6), c = 15.8416(1) Å (hexagonal setting) and V = 3164.1 Å(3). These smaller cells correspond to average structures and hence the X-ray data do not account for the difference in the structures of the two different complex ions. However, when analysing neutron powder diffraction data, it is possible to distinguish between the two complex ions using a trigonal R3 cell with a = 15.1865(1) and c = 15.8416(1) Å (hexagonal setting). In a Rietveld type structure model refinement with a total of 28 atom sites (4 Bi, 3 N, 15 O and 6 H), the composition of this sample is determined to be [Bi(6)O(4)(OH)(4)](0.54(1))[Bi(6)O(5)(OH)(3)](0.46(1))(NO(3))(5.54(1)).