Cationic lead(II) halide complexes in molten alkali-metal nitrate. Part 3.—The structure of Pb2X3+ and the solvated PbII ion, determined by liquid X-ray scattering and raman spectroscopy

Abstract

Liquid X-ray scattering and Raman spectroscopy measurements have been made at 280 °C on binary and ternary mixtures in the system PbX₂–Pb(NO₃)₂–(K,Na)NO₃, where X = F, Cl, or Br. The furnaces and experimental techniques are described. The nitrate coordination of Pb(II) is shown to be Pb(NO₃)^2–₄ in halide-free melts of Pb(NO₃)₂–(K,Na)NO₃. The nitrate ions are asymmetrically bound via two oxygen atoms at distances of 2.4 and 3.1 Å and the lead(II) atoms is positioned slightly out of the nitrate plane. In melts containing halide ions X^– complexes of formal composition Pb₂X³⁺ are formed, with Pb—X—Pb angles of 84 and 81° for Pb₂Cl³⁺ and Pb₂Br³⁺, respectively. In Pb₂F³⁺ only the Pb—Pb distance can be experimentally determined. The Pb—F—Pb angle ranges between 96 and 139°. A remarkable characteristic of these complexes is the occurrence of very shot Pb—Pb distance of 3.4–3.8 Å, suggesting a significant metal–metal interaction.