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/PbCl2in [BMIm]Cl/[BMPyr]Cl/AlCl3-based ionic liquids. The colourless crystals of the title compounds contain infinite1∞[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 luminescencevias-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+.