Alcohol-solvothermal syntheses, crystal structures and photocatalytic properties of tin selenides with polyselenide ligands

Abstract

Diselenide-containing selenidostannates [TM(en)3]Sn3Se6(Se2) (TM = Mn (1), Fe (2), and Zn (3)) and [Ni(en)3]Sn3Se7.5 (4) (en = ethylenediamine) were prepared by the reactions of TMCl2, SnCl4·5H2O, Se and en in C2H5OH solvent under solvothermal conditions. The same reaction in C2H5OH/PEG-200 mixed solvent produced novel polyselenidostannates [TM(en)3][Sn(Se4)3] (TM = Mn (5), Fe (6), Zn (7), and Ni (8)). In 1–3, the interconnections of semi-cubic Sn3Se4 building units via four μ-Se2− and two μ-Se22− bridges give rise to the polymeric lamellar [Sn3Se6(Se2)]n2n− anion. The 1-D [Sn3Se7.5]n2n− anionic chain in 4 is built from the semi-cubic Sn3Se4 units interlinked by three μ-Se bridges and one μ-Se2 bridge at two Sn atoms with the third Sn atom being coordinated by a terminal Se2− anion. All the Sn4+ ions of [Sn3Se6(Se2)]n2n− are in five-fold coordination forming trigonal bipyramidal SnSe5 units, while both trigonal bipyramidal SnSe5 and tetrahedral SnSe4 units are observed in the 1-D [Sn3Se7.5]n2n− anion. In 5–8 the Sn4+ ion is chelated by three tetraselenide Se42− ligands, forming a [Sn(Se4)3]2− anion with the Sn4+ ion in an octahedral SnSe6 geometry. All the SnSe4 chelating rings of the [Sn(Se4)3]2− anion are in a half-chair conformation. The polymeric selenidostannates 1–4 are potential semiconductors with band gaps in the range of 2.04–2.18 eV. Compounds 5–8 have narrow band gaps between 1.55 eV and 1.74 eV, and exhibit distinct red shifts compared with the absorption edges of the layered selenidostannates 1–4. The manganese and iron compounds exhibit photocatalytic activities in the photodegradation of organic dye methylene blue (MB) under visible light irradiation at room temperature. The thermal decomposition residues of the manganese and iron compounds display higher catalytic activities than their precursors in the photodegradation of MB.