A basic bismuth(III) nitrate with the composition [Bi₆O₄(OH)₄]_0.5[Bi₆O₅(OH)₃]_0.5(NO₃)_5.5 formed in a slow crystal growth mode has an ordered crystal structure with the monoclinic space group P2₁ 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 ų (Henry et al. 2003). In a very fast crystal growth mode the complex ions disorder in another P2₁ 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 ų. 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 ų and a trigonal R cell with a = 15.18650(6), c = 15.8416(1) Å (hexagonal setting) and V = 3164.1 ų. 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 R 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 [Bi₆O₄(OH)₄]_0.54(1)[Bi₆O₅(OH)₃]_0.46(1)(NO₃)_5.54(1).