Silicon-29 NMR Studies of Tetraalkylammonium Silicate Solutions. 1. Equilibria, (29)Si Chemical Shifts, and (29)Si Relaxation.
The addition of tetraalkylammonium cations to aqueous silicate solutions enhances the abundance of symmetric, cagelike, polysilicate anions including the cubic octamer, Si(8)O(20)(8)(-). The equilibrium ratio of tetramethylammonium (TMA) cations to the octameric silicate anion is 8:1 for solutions with a concentration ratio [OH(-)]:[Si] >/= 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.
Kinrade
Stephen D.
SD
Department of Chemistry, Lakehead University, Thunder Bay, Ontario, P7B 5E1, Canada, and School of Chemical Sciences, University of Illinois at Urbana-Champaign, 505 South Mathews Avenue, Urbana, Illinois 61801.
Knight
Christopher T. G.
CT
Pole
David L.
DL
Syvitski
Raymond T.
RT