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]Sn₃Se_7.5 (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 [Sn₃Se_7.5]_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 [Sn₃Se_7.5]_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.