Synthesis, structure and 77Se/ 119Sn NMR spectroscopy of the new polyselenide, tris(tetraselenido)stannate(IV), [Sn(Se 4) 3] 2−

Abstract

The reaction of sodium pentaselenide with SnCl 4 or SnCl 2·2H 2O in dimethylformamide (DMF), in a 3:1 ratio, forms the new soluble anion [Sn(Se 4) 3] 2− in high (>79%) yields. The compound (Ph 4P) 2[Sn(Se 4) 3] ( I) crystallizes in the monoclinic space group P2 1/ c with unit cell dimensions, a = 13.320(2), b = 11.678(3), c = 34.817(9) Å, β = 98.85(2)° and V = 4535 Å 3. A single-crystal X-ray diffraction study of I shows that three chelating Se 4 2− ligands provide an octahedral coordination about the central Sn 4+ atom. The crystal structure was solved and refined with conventional techniques to R = 6.0% and Rw = 7.0%. The average SnSe distance is 2.709(13) Å, while the average SeSe bond distance is 2.324(12) Å. The IR spectrum of I (CsI pellet) shows two sets of absorptions at 273, 256 cm −1 and 181, 173 cm −1, respectively, assigned tentatively to ν(SeSe) and ν(SnSe) vibrations. The 119Sn NMR spectrum of I in DMF, shows a single resonance at − 723 ppm (vs Me 4Sn). The 77Se NMR spectrum of I in DMF, shows two resonances at 618 and 459 ppm. Thermal decomposition of I results in formation of SnSe 2 at 510°C. Further heating, above 600°C, results in SnSe.