New sterically hindered tin(iv) siloxane precursors to tinsilicate materials: synthesis, spectral, structural and photocatalytic studies

Abstract

A series of sterically hindered tin(IV) siloxanes were synthesized by the reaction between tris(tert-butoxy)silanol/tri-phenylsilanol and organotin chlorides {[(^tBu)₂Sn(OSi(O^tBu)₃)₂] (1), [(^tBu)₂Sn(OSi(O^tBu)₃)Cl] (2), [(n-Bu)₂Sn(OSi(O^tBu)₃)₂] (3), [(n-Bu)₂Sn(OSi(O^tBu)₃)Cl] (4), [(Me)₂Sn(OSi(O^tBu)₃)₂] (5), [(Me)₂Sn(OSi(O^tBu)₃)Cl] (6), [(^tBu)₂Sn(OSiPh₃)₂] (7), [(^tBu)₂Sn(OSiPh₃)Cl] (8) whereas ^tBu = tertiary butyl; n-Bu = butyl; Me = methyl}. All the compounds were characterized by analytical and spectroscopic (FT-IR and ¹H, ¹³C, ²⁹Si, ¹¹⁹Sn NMR) methods. Compounds 1 and 7 were structurally characterized by single-crystal X-ray crystallography. The coordination geometry of tin (SnO₂C₂) is slightly distorted from tetrahedral due to sterically crowded ligands around the tin atom. In order to convert tinsilicate materials, compounds 1 and 3 were selected for thermolysis to give identical SnO₂·2SiO₂ materials at low temperature (∼350 °C). The degradation was investigated by thermal analysis (TGA/DTA), both compounds having butyl groups which facile eliminate to butene gas via a β-hydride elimination process (∼250 °C). The molecular route to oxide materials at low temperature described here represents an alternative to the sol–gel technique. The tinsilicate material was examined by several techniques including infrared, powder X-ray diffraction analysis (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The optical band gap of the material has been studied by UV-vis-NIR spectroscopy and the result is a low band gap value (E_g = 2.549 eV) due to the silicon oxide mixed with tin oxide. The prepared material acts as photocatalyst for the degradation of methylene blue (MB).