Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. 12. A potentiometric and 29Si-NMR study of silicon tropolonates

Abstract

Complexation in the H +-Si(OH) 4-tropolone (HL) system was studied in 0.6 M (Na)Cl medium at 25° C. Speciation and formation constants were determined from potentiometric (glass electrode) and 29Si-NMR data. Experimental data cover the ranges 1.5 ⩽ - log[H +] ⩽ 8.4, 0.002 ⩽ B ⩽ 0.012 M, and 0 ⩽ C ⩽ 0.060 M ( B and C stand for the total concentration of Si and tropolone, respectively). In acid solutions (-log[H +] ⩽ 3) a hexacoordinated cationic complex, SiL 3 +, is formed with log K(Si(OH) 4 + 3HL + H + XXX SiL 3 + + 4H 2O) = 7.08 ± 0.03. Furthermore, the formation of a disilicic acid was established from 29Si-NMR data. The dimerization constant of Si(OH) 4 was found to be 10 exp (1.2 ± 0.1). In model calculations the solubility of quartz and amorphous SiO 2 in the presence of tropolone is demonstrated. Data were analyzed using the least-squares computer program LETAGROPVRID.