Synthesis and spectroscopic characterization of tris(<i>tert</i>-butoxy)siloxy titanium and hafnium complexes: Molecular precursor to [M/Si/O (M = Ti, Hf)] materials

<p></p> <p>The reaction of one equivalent of metallocene dichloride Cp<sub>2</sub>MCl<sub>2</sub> (M = Ti, Hf) with two molar equivalents of sodium salt of tri(<i>tert</i>-butoxy)siloxane, (<i><sup>t</sup></i>BuO)<sub>3</sub>SiONa, in toluene yields Cp<sub>2</sub>Ti[OSi(O<i><sup>t</sup></i>Bu)<sub>3</sub>]<sub>2</sub> (<b>1</b>) and Cp<sub>2</sub>Hf[OSi(O<i><sup>t</sup></i>Bu)<sub>3</sub>]<sub>2</sub> (<b>2</b>). These compounds were characterized by analytical and spectroscopic techniques (C/H/N analysis, FT-IR, NMR, EI-MS, and thermal analysis). An independent thermolysis of <b>1</b> and <b>2</b> at low temperature resulted in the formation of the corresponding metal silicates MO<sub>2</sub>·2 SiO<sub>2</sub> [M = Ti (<b>3</b>) and Hf (<b>4</b>)] as evidenced by infrared spectroscopy, powder X-ray diffraction analysis (PXRD), and scanning electron microscopy (SEM). These thermally stable amorphous metal silicate materials (<b>3</b> and <b>4</b>), albeit exhibiting moderate surface areas, are found to be microporous by N<sub>2</sub> adsorption studies. UV-vis-NIR spectroscopy shows low energy band gap E<sub>g</sub> = 2.63 eV for <b>3</b> and 2.99 eV for <b>4</b> due to the silicon oxide mixed with the corresponding transition metal oxides. The photocatalytic activity of titanium silicate material (<b>3</b>) has been explored in terms of degradation of methylene blue.</p>