Tin Bromido Aluminate Networks with Bright Luminescence

Abstract

The novel tin bromido aluminates [Sn3(AlBr4)6](Al2Br6) (1), Sn(AlBr4)2 (2), [EMIm][Sn(AlBr4)3] (3) and [BMPyr][Sn(AlBr4)3] (4) ([EMIm]: 1-ethyl-3-methylimidazolium, [BMPyr]: 1-butyl-1-methyl-pyrrolidinium), are obtained from a ionic-liquid-based reaction of AlBr3 and SnCl2 or SnBr2, resulting in colorless and transparent crystals. 1 contains a neutral, inorganic ∞3[Sn3(AlBr4)6] network filled with intercalated Al2Br6 molecules. 2 represents a 3D structure isotypic to Pb(AlCl4)2 or α-Sr[GaCl4]2. 3 and 4 exhibit infinite ∞1[Sn(AlBr4)3]n− chains that are separated by the voluminous [EMIm]+/[BMPyr]+ cations. All title compounds contain Sn2+ coordinated by AlBr4 tetrahedra, resulting in chains or 3D networks. Moreover, all title compounds show photoluminescence due to Br−→Al3+ ligand-to-metal charge-transfer excitation, followed by 5s2p0←5s1p1 emission on Sn2+. Most surprisingly, the luminescence is highly efficient (quantum yield >50 %). Specifically, 3 and 4 exhibit outstanding quantum yields of 98 and 99 %, which are the highest values observed for Sn2+-based luminescence so far. The title compounds have been characterized by single-crystal structure analysis, elemental analysis, energy-dispersive X-ray analysis, thermogravimetry, infrared and Raman spectroscopy, UV-Vis and photoluminescence spectroscopy.