SYNTHESIS AND CHARACTERIZATION OF DIANIONIC HEXACOORDINATE SILICON(IV) COMPLEXES OF SUBSTITUTED CATECHOLS, FLAVONES, AND FLUORONE: X-RAY CRYSTAL STRUCTURES OF [(n-C3H7)2NH2]2[(Cl4C6O2)3Si] • 3 CH3CN AND [(n-C3H7)2NH2]2[(Br4C6O2)3Si] • 2 (CH3)2SO

Reaction of tetraethoxysilane (TEOS) with substituted catechols (I-X), 7,8-dihydroxyflavone (XI), 3,3',4'-trihydroxyflavone (XII), 3',4',5,7-tetrahydroxyflavone (XIII), and 9-phenyl-2,3,7-trihydroxy-6-fluorone (XIV) in the presence of an amine (molar ratio 1:3:2) in acetonitrile affords the corresponding dianionic hexacoordinate silicon(IV) complexes 1-15 having a SiO6 structural fragment. The dianionic silicates were isolated as di-n-propylammonium/triethylammonium/di-n-butylammonium salts and were characterized by elemental analysis and various spectroscopic data (IR, H-1, C-13, and Si-29 NMR). The solid state structures of compounds [(n-C3H7)(2)NH2](2)[{Cl4C6O2}(3)Si] (1) and [(n-C3H7)(2)NH2](2)[{Br4C6O2}(3)Si] (2) were determined by single crystal X-ray diffraction. Both 1 and 2 crystallize in the monoclinic space group C2/c and reveal (i) bidentate mode of ligation, (ii) octahedral coordination around silicon, and (iii) hydrogen bonding features.