[Bi₂O₂]²⁺ Layers in Bi₂O₂(OH)(NO₃): Synthesis And Structure Determination

Bi₂O₂(OH)(NO₃) is the first bismuth oxynitrate containing [Bi₂O₂]²⁺ layers for which the crystal structure has been determined. The current study presents its synthesis, formula determination using powder XRD, thermogravimetric analysis and nitrate assay, and finally, crystal structure refinement from twinned crystals. Bi₂O₂(OH)(NO₃) crystallizes in the orthorhombic system, a = 5.3878(11), b = 5.3984(10) and c = 17.136(2) Å , with the space group Cmc2₁. The structure refinement based on 1257 independent reflections converged to R_I (obs) = 0.0321 and R_Iw (obs) = 0.0765. The Bi₂O₂(OH)(NO₃) structure is based on [Bi₂O₂]²⁺ sheets in the (ab) plane. The interlayer space is composed of two slices containing OH⁻ and (NO₃)⁻ groups, respectively. Within the nitrate layers, the disorder over two possible NO^3- orientations (related by a four fold axis) involves half occupied positions for two of the oxygen atoms. An attempt to lower the symmetry and/or enlarge the unit cell, looking for an (NO₃)⁻ ordering, failed