Silicon-29 NMR studies of tetraalkylammonium silicate solutions.: 1.: Equilibria, 29Si chemical shifts, and 29Si relaxation

The addition of tetraalkylammonium cations to aqueous silicate solutions enhances the abundance of symmetric, cagelike, polysilicate anions including the cubic octamer, Si8O208-. The equilibrium ratio of tetramethylammonium (TMA) cations to the octameric silicate anion is 8:1 for solutions with a concentration ratio [OH-]:[Si] greater than or equal to 1:1. Evidence indicates that organocations directly associate with cagelike polyanions to form a protective shell of hydrophobic hydration that impedes hydrolysis of the central anion.