Transformation of molecular compounds with Ba(Sr)/Al/Si and Ca(Sr, Ba)/Ti(Zr, Hf)/Si heteroelements as new efficient route to metal silicate materials

Silicon-based moieties were anchored in heterometallic alkoxide platforms to obtain molecular clusters based on the M-O-M-O-Si motif for the generation of mixed-metal silicate materials. Single-source molecular precursors with structures [M{(-ddbfo)(2)Al(OSiPh3)(2)}(2)], where dbbfoH = 2,3-dihydro-2,2-dimethylbenzofuran-7-ol and M = Ba (1), Sr (2), [Sr4Ti2((6)-O)((3),(2)-OCH2CH2OMe)(8)(-OCH2CH2OMe)(2)(OSiPh3)(4)] (3), [Sr4M2((4)-OH)((3),(2)-OCH2CH2OMe)(4)(,(2)-OCH2CH2OMe)(6)(-X)(OSiPh3)(4)] (4, with M = Zr and X = Cl; 5 with M = Hf and X = OH), [Sr3Hf2((5)-O)((3),(2)-OCH2CH2OMe)(4)(OCH2CH2OMe)(4)(OSiPh3)(4)] (6), and [Ca2M2((3)-OH)(2)(,(2)-OCH2CH2OMe)(4)((2)-HOCH2CH2OMe)(2)(-OCH2CH2OMe)(2)(OSiPh3)(4)] for M = Zr (7), Hf (8), were prepared by substitution of methyl groups, using Ph3SiOH or chloride atoms with KOSiPh3, in [M{(-ddbfo)(2)AlMe2}(2)] (M = Sr, Ba) or [M4M2((6)-O)((3),(2)-OCH2CH2OMe)(8)(OCH2CH2OMe)(2)(HOCH2CH2OMe)(x)Cl-4] (M = Ca, Sr, Ba, M = Ti, Zr, Hf and x = 0, 4). The precursors were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray structural analysis. Thermal decomposition of compounds 1-8 at 1000 degrees C led to formation of ceramic materials that consisted of mixed-metal oxide nanocrystallites embedded in an amorphous SiO2 matrix. Compounds 1 and 2 decomposed to BaAl2Si2O8 and SrAl2Si2O8 aluminosilicates, 4 gave a mixture of SrSiO3, ZrO2, SrZrO3 and Sr7ZrSi6O21, 5 and 6 gave mixtures of various compounds, including SrHfO3, Hf0.96Si0.04O2, and SiO2, 7 lead to CaZrO3, ZrO2 and Ca3ZrSi2O9 and 8 gave a HfO2, Ca2HfSi4O12 and SiO2 phase. The thermolysis of compound 3 gave SiO2 particles of average size 40-90 nm, which contained spherical SrTiO3, SrSiO3 and Sr2TiSi2O8 nanocrystallites of diameter 5-16 nm.