No abstract

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 [Pb(n)Bi(10-n)O13][Bi2O2](n)Cl(4+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 σ ∼ 10(-3) S cm(-1) at 650 °C and suggests a contribution of Cl(-) in the diffusion process. Most remarkable, PbBi4O6Cl2 as well as [Pb2Bi8O13][Bi2O2]2Cl6 show very bright red emission at low temperature, which could be assigned to Bi(3+) transitions by comparison to BaBi4O6Cl2. The different shapes of the excitation spectra lead to the assumption of a complete Pb-Bi energy transfer.

The reactions between PbO, Bi 2 O 3 (or BiOCl), and SeO 2 by the chemical vapor transport method using HCl as a transporting agent afforded three novel bismuth/lead chloroselenites, namely, β-BiSeO 3 Cl (1), Bi 6 (SeO 3 ) 4 Cl 10 (2), and PbBi 10 (SeO 3 ) 12 Cl 8 (3). Compound 1 is noncentrosymmetric (space group Cc, SHG active) and has a giant unit cell (V = 19792(2) Å 3 ). In the context of the complex BiSeO 3 Cl phase diagram reported by Oppermann et al., it was assigned to the undescribed β-form on the basis of its IR spectra and powder X-ray diffraction pattern. The comparison between the α-, β-, and γ-forms suggests their formation via the condensation of volatile Bi(SeO 3 )Cl molecules. Analysis of the structures of the α-, β-, and γ-forms indicates that the α → β → γ phase transitions are associated with a dramatic fluctuation of structural complexity together with the transitional character of the β phase. Compounds 1 and 3 are layered compounds with identical ([M 8 Cl 16 ] 8+ and [M 14 (SeO 3 ) 24 ] 6− ) layers, where M stands for Bi in 1 and Pb/Bi in 3. There are additional [Bi 12 Cl 32 ] 4+ layered subunits in 1. The crystal structure of 2 consists of the [Bi 6 (SeO 3 ) 4 Cl 10 ] building blocks forming an open framework with six-membered-ring channels. These three compounds complete the poorly known bismuth selenium oxochloride panorama.