New [PbBi2O4][Bi2O2]Cl2 and [PbnBi10-nO13][Bi2O2]nCl4+n Series by Association of Sizable Subunits: Relationship with Arppe's Compound Bi24O31Cl10 and Luminescence Properties

Four new mixed lead-bismuth oxychloride compounds have been prepared and characterized by single crystal X-ray diffraction. Their crystal structures are described on the basis of the association of distinct building units found in parent Pb or Bi oxychlorides. The new compound PbBi4O6Cl2 is formed of the stacking of 2D positive [Bi2O2](2+) layers and neutral [PbBi2O4](0) double layers separated by Cl- anions. Similar motifs with finite lengths are combined together in the new series [PbnBi10-nO13][Bi2O2](n)Cl4+n. From the structural viewpoint, it is striking that this family of homologous phases is strongly related to Bi24O31Cl10 well-known as Arppe's compound in which the fluorite-like [Bi2O2](n) subunit was increased from n = 1 (mixed Bi/Pb Arppe's compound) to n = 2, 3, and 4 new members. The preparation of the respective powders shows the predominant stability of the n = 2 term which was prepared as a single-phase, while other terms have not been obtained in absence of secondary phases. For n = 2, the impedance spectroscopy shows a conductivity value sigma similar to 10(-3) S cm(-1) at 650 degrees C and suggests a contribution of Cl- in the diffusion process. Most remarkable, PbBi4O6Cl2 as well as [Pb2Bi8O13][Bi2O2](2)Cl-6 show very bright red emission at low temperature, which could be assigned to Bi3+ transitions by comparison to BaBi4O6Cl2. The different shapes of the excitation spectra lead to the assumption of a complete Pb-Bi energy transfer.