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

[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)(infinity)[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+.

Automated summary

The newly synthesized compounds in ionic liquids exhibit unique structural arrangements and efficient white-light emission, showing rare high luminescence efficiency through s-p transitions.