Formation of subvalent bismuth cations in molten gallium trichloride and benzene solutions

Abstract

Liquid GaCl₃ and GaCl₃–NaCl mixtures oxidize bismuth metal to subvalent bismuth cations and such species are also formed in Bi–GaCl₃–benzene and Bi–BiCl₃–GaCl₃–benzene solutions at room temperature. In Bi–GaCl₃ and Bi–GaCl₃–NaCl melts, ⁷¹Ga NMR, UV–VIS and Raman spectroscopy identify Ga⁺, halogallate(III) ions, Bi⁺ and the cluster Bi₅³⁺ as reaction products and Bi₅(GaCl₄)₃ can be crystallized from Bi–GaCl₃ melts. Furthermore, Raman spectra and powder diffraction data or quenched samples of the Bi–GaCl₃ system give evidence for the formation of more reduced bismuth clusters at high formal bismuth concentrations. In benzene solution, Bi⁺ and Bi₅³⁺ are formed; no evidence for other, more reduced, species are found. In order to interpret the ⁷¹Ga NMR and Raman spectra of the Bi–GaCl₃–benzene system properly, a detailed investigation of the Ga–GaCl₃–benzene system was undertaken. The spectroscopic data from this system support the view that the chlorogallate (III) ion accompanying the subvalent ions Ga⁺ and Bi₅³⁺ in Bi–GaCl₃–benzene solution is Ga₃Cl₁₀^–. Liquid X-ray scattering (LXS) measurements confirm the speciation of the Bi–GaCl₃–benzene system and show that the structure of Bi₅³⁺ is virtually identical with that in the solid state. Interactions between Bi₅³⁺ and the aromatic solvent are evident from a Raman band at 986 cm^–1 next to the most intense band of C₆H₆ at 992 cm^–1. However, LXS and ¹³C NMR are inconclusive as to the nature of this interaction. Upon dilution of Bi–GaCl₃–benzene solutions by n-heptane, a new modification of Bi₅(GaCl₄)₃ precipitates, as shown by powder diffraction. Rietveld analysis shows this modification to possess cubic symmetry (Fm3c, a= 17.114 Å) and a high degree of structural disorder.