NUCLEAR-MAGNETIC-RESONANCE STUDIES OF SILICON(IV) COMPLEXES IN AQUEOUS-SOLUTION .2. TRIS-TROPOLONATO AND TRIS-3-HYDROXYPYRIDIN-4-ONATO COMPLEXES

Quantitative data for the reaction: 3LH + Si(OH)4 + H+ half-arrow-right-over-half-arrow-left [SiL3]+ + 4H2O in aqueous solution have been obtained by H-1 NMR spectroscopy, where LH = tropolone, 4-methyltropolone, 3-hydroxy-2-methylpyridin-4-one, 1,2-dimethyl-3-hydroxypyridine-4-one and 1-ethyl-3-hydroxy-2-methylpyridin-4-one. Equilibrium studies were carried out in D2O solutions for both types of complex. The measurements for the complexes derived from 3-hydroxypyridin-4-ones were repeated in H2O and the results are compared with the D2O data. We present the first air-stable organic substrate capable of etching glass at a significant rate in non-fluorinated acidic solution. The dissolution of silica was confirmed by the detection of the Si-29 NMR resonance characteristic of the six-coordinate silicon(IV) complex formed. Information has been obtained on the rate of dissolution of glass by 1-ethyl-3-hydroxy-2-methylpyridin-4-one in acid solution.