Six Coordinate Tris(catecholato)silicates of Primary Amine Residues—Synthesis, Characterization, and Thermolysis Studies. X-Ray Structures of [n-C₃H₇NH₃]₂[Si(C₆H₄O₂)₃]·1/2(C₆H₁₄N₂) and of a Bulky Secondary Ammonium Ion, [(i-C₄H₉)₂NH₂]₂[Si(C₆H₄O₂)₃]·H₂O

Abstract

Synthesis of the hypervalent tris(catecholato)silicate ion, [(C₆H₄O₂)₃-Si]²⁻ having five different primary ammonium cations viz. n-propylammonium (1), isopropylammonium (2) n-butylammonium (3), cyclohexylammonium (4), benzylammonium (5), and a bulky secondary ammonium cation, namely diisobutylammonium (6), have been achieved by the reaction of catechol and tetraethoxysilane (TEOS) in presence of the corresponding amine. Elemental analysis, IR, NMR (¹H, ¹³C, and ²⁹Si), and mass spectral data have been used for their characterization. Single crystal x-ray structures of 1 and 6 indicate nearly same distortion of the “SiO₆” octahedron but interesting differences in the hydrogen bonding interactions arising from the catecholato oxygens and the N—H bonds of the ammonium cations. While compound 1 exhibits hydrogen bonding more discretely and by revealing strong interaction between the n-propylammonium ions, compound 6 shows an extended intermolecular hydrogen bonding aided by a water molecule present in the lattice to lead to infinite one dimensional chain arrangement. TG and EG analyses of compounds, 1–5 indicate 1) the formation of the previously observed spirosilane intermediate, [Si(C₆H₄O₂)₂] and 2) their less thermal stability compared to those having secondary or tertiary ammonium cations.

Keywords:

• Hydrogen bonding
• primary amine residues
• six coordinate silicates
• thermal behavior
• x-ray structure