New [PbBi₂O₄][Bi₂O₂]Cl₂ and\n[Pb_nBi_10‑nO₁₃][Bi₂O₂]_<i>n</i>Cl_4+<i>n</i> Series by Association of Sizable Subunits: Relationship with\nArppe’s Compound Bi₂₄O₃₁Cl₁₀ and Luminescence Properties

Abstract

Four\nnew mixed lead–bismuth oxychloride compounds have been prepared\nand characterized by single crystal X-ray diffraction. Their crystal\nstructures are described on the basis of the association of distinct\nbuilding units found in parent Pb or Bi oxychlorides. The new compound\nPbBi₄O₆Cl₂ is formed of the stacking\nof 2D positive [Bi₂O₂]²⁺ layers and\nneutral [PbBi₂O₄]⁰ double layers\nseparated by Cl^– anions. Similar motifs with finite\nlengths are combined together in the new series [Pb_<i>n</i>Bi_{10‑<i>n</i>}O₁₃]­[Bi₂O₂]<i>_n</i>Cl_4+<i>n</i>. From the structural viewpoint, it is striking that\nthis family of homologous phases is strongly related to Bi₂₄O₃₁Cl₁₀ well-known as Arppe’s compound\nin which the fluorite-like [Bi₂O₂]<i>_n</i> subunit was increased from <i>n</i> =\n1 (mixed Bi/Pb Arppe’s compound) to <i>n</i> = 2,\n3, and 4 new members. The preparation of the respective powders shows\nthe predominant stability of the <i>n</i> = 2 term which\nwas prepared as a single-phase, while other terms have not been obtained\nin absence of secondary phases. For <i>n</i> = 2, the impedance\nspectroscopy shows a conductivity value σ ∼ 10^–3 S cm^–1 at 650 °C and suggests a contribution\nof Cl^– in the diffusion process. Most remarkable,\nPbBi₄O₆Cl₂ as well as [Pb₂Bi₈O₁₃]­[Bi₂O₂]₂Cl₆ show very bright red emission at low temperature,\nwhich could be assigned to Bi³⁺ transitions by comparison\nto BaBi₄O₆Cl₂. The different shapes\nof the excitation spectra lead to the assumption of a complete Pb–Bi\nenergy transfer.