Synthesis, structure, and photoluminesence of the chloridoaluminates [BMIm][Sn(AlCl4)3], [BMPyr][Sn(AlCl4)3], and [BMIm][Pb(AlCl4)3]

Abstract

[BMIm][Sn(AlCl₄)₃] (1) ([BMIm]: 1-butyl-3-methylimidazolium), [BMPyr][Sn(AlCl₄)₃] (2) ([BMPyr]: 1-butyl-1-methyl-pyrrolidinium), and [BMIm][Pb(AlCl₄)₃] (3) are obtained by reaction of SnCl₂/PbCl₂ in [BMIm]Cl/[BMPyr]Cl/AlCl₃-based ionic liquids. The colourless crystals of the title compounds contain infinite ¹_∞[M(AlCl₄)₃]ⁿ⁻ chains (M: Sn, Pb) that are separated by the voluminous [BMIm]⁺/[BMPyr]⁺ cations. The central Sn²⁺/Pb²⁺ is coordinated by chlorine in the form of distorted squared anti-prismatic polyhedra. Each Cl atom, in turn, is part of an [AlCl₄]⁻ tetrahedron that interlinks Sn²⁺/Pb²⁺ to the chain-like building unit. In addition to the novel structural arrangement, all title compounds surprisingly show intense white-light emission. Although Sn²⁺ and Pb²⁺ are well-known as dopants in conventional phosphors, efficient luminescence via s–p-transitions of compounds containing Sn²⁺/Pb²⁺ in molar quantities and as regular lattice constituents is rare. The emission of [BMIm][Sn(AlCl₄)₃] and [BMPyr][Sn(AlCl₄)₃] is very efficient with quantum yields of 51 and 76%, which belong to the highest values known for s–p-based luminescence of Sn²⁺.