Tin Bromido Aluminate Networks with Bright Luminescence.

Abstract

The novel tin bromido aluminates [Sn3 (AlBr4 )6 ](Al2 Br6 ) (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 Al2 Br6 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 5s2 p0 ←5s1 p1 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.