Synthesis and Characterization of Tris(catecholato)Silicates,[(C 6 H 4 O 2 ) 3 Si] 2− with Different Counter Cations – First Pyrolysis Study and X-ray Structure of [{(CH 3 ) 2 CH} 2 NH 2 ] 2 [(C 6 H 4 O 2 ) 3 Si] · 2CH 3 CN · H 2 O

Abstract

The synthesis of hypervalent tris(catecholato)silicate ion, [(C₆H₄O₂)₃Si]²⁻ with six different counter cations: (i) diethylammonium (I), (ii) triethylammonium (II), (iii) diisopropylammonium (III), (iv) morpholinium (IV), (v) piperazinium (V) and (vi) N-methylpiperazinium (VI) has been achieved (yield: ca.95%) by the reaction of catechol and tetraethoxysilane in presence of the corresponding amine. Single crystal X-ray structure of compound (III) has been determined. It crystallizes in orthorhombic system [space group P2₁2₁2₁; a = 11.735(2), b = 13.708(3), c = 23.283(5) Å α = 90°, β = 90°, γ = 90°; Volume = 3745.4(11) ų; Density = 1.165 gcm⁻³; Z = 4; R = 0.0585; wR2(I) = 0.1610 and 3677 reflections] and the structure shows slightly distorted octahedral geometry around silicon. Results of TG, DT and EG analysis of compounds (I) – (VI) reveal the influence of the counter cation on thermal stability. Bench scale pyrolysis of (I) and (II) convert them to [(C₆H₄O₂)₂Si]_n by the quantitative expulsion of ammonium catecholate salt, (M⁺)₂[(C₆H₄O₂)]²⁻. CP-MAS ²⁹Si-nmr spectral data suggests that [(C₆H₄O₂)₂Si]_n is a simple mixture.