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{(μ-ddbfo) 2 Al(OSiPh 3 ) 2 } 2 ], where dbbfoH = 2,3-dihydro-2,2-dimethylbenzofuran-7-ol and M = Ba ( 1 ), Sr ( 2 ), [Sr 4 Ti 2 (μ 6 -O)(μ 3 ,η 2 -OCH 2 CH 2 OMe) 8 (η-OCH 2 CH 2 OMe) 2 (OSiPh 3 ) 4 ] ( 3 ), [Sr 4 M′ 2 (μ 4 -OH)(μ 3 ,η 2 -OCH 2 CH 2 OMe) 4 (μ,η 2 -OCH 2 CH 2 OMe) 6 (μ-X)(OSiPh 3 ) 4 ] ( 4 , with M′ = Zr and X = Cl; 5 with M′ = Hf and X = OH), [Sr 3 Hf 2 (μ 5 -O)(μ 3 ,η 2 -OCH 2 CH 2 OMe) 4 (OCH 2 CH 2 OMe) 4 (OSiPh 3 ) 4 ] ( 6 ), and [Ca 2 M′ 2 (μ 3 -OH) 2 (μ,η 2 -OCH 2 CH 2 OMe) 4 (η 2 -HOCH 2 CH 2 OMe) 2 (η-OCH 2 CH 2 OMe) 2 (OSiPh 3 ) 4 ] for M′ = Zr ( 7 ), Hf ( 8 ), were prepared by substitution of methyl groups, using Ph 3 SiOH or chloride atoms with KOSiPh 3 , in [M{(μ-ddbfo) 2 AlMe 2 } 2 ] (M = Sr, Ba) or [M 4 M′ 2 (μ 6 -O)(μ 3 ,η 2 -OCH 2 CH 2 OMe) 8 (OCH 2 CH 2 OMe) 2 (HOCH 2 CH 2 OMe) 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 °C led to formation of ceramic materials that consisted of mixed-metal oxide nanocrystallites embedded in an amorphous SiO 2 matrix. Compounds 1 and 2 decomposed to BaAl 2 Si 2 O 8 and SrAl 2 Si 2 O 8 aluminosilicates, 4 gave a mixture of SrSiO 3 , ZrO 2 , SrZrO 3 and Sr 7 ZrSi 6 O 21 , 5 and 6 gave mixtures of various compounds, including SrHfO 3 , Hf 0.96 Si 0.04 O 2 , and SiO 2 , 7 lead to CaZrO 3 , ZrO 2 and Ca 3 ZrSi 2 O 9 and 8 gave a HfO 2 , Ca 2 HfSi 4 O 12 and SiO 2 phase. The thermolysis of compound 3 gave SiO 2 particles of average size 40-90 nm, which contained spherical SrTiO 3 , SrSiO 3 and Sr 2 TiSi 2 O 8 nanocrystallites of diameter 5-16 nm. The heterometallic alkoxides based on M-O-M′-O-Si motif were used for the preparation of ceramic materials consisting of mixed metal oxide nanocrystallites embedded in SiO 2 matrix.