Tin Bromido Aluminate Networks with Bright Luminescence

The novel tin bromido aluminates [Sn-3(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)(infinity)[Sn-3(AlBr4)(6)] network filled with intercalated Al2Br6 molecules. 2 represents a 3D structure isotypic to Pb(AlCl4)(2) or alpha-Sr[GaCl4](2). 3 and 4 exhibit infinite (1)(infinity)[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 5s(2)p(0)<- 5s(1)p(1) 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.