Lesley S. Dent Glasser

Silicon-29 and carbon-13 NMR studies of organosilicon chemistry: X. The structure of Si8O11(OSiMe3)10

Abstract Trimethylsilylation of tetramethylammonium silicate produced a compound of formula C 30 H 90 O 21 Si 18 . NMR studies using the 13 C and 29 Si nuclei have shown that the structure of this compound is related to a double four-membered cage by the replacement of one SiOSi bridge by trimethylsiloxy units.

The unexpected behaviour of potassium aluminosilicate solutions

Potassium aluminosilicate solutions with low Si:Al ratios form gels more slowly with increasing KOH content but at higher Si:Al ratios the reverse is true; there are also significant differences in other solution properties.

Silicate species in solution. Part 1. Experimental observations

Changes in the pH or concentration of sodium silicate solutions produce changes in the degree of polymerisation of the silicate species, and these have been followed by the technique of trimethylsilylation. Provided that the pH remains relatively high, above ca. 10 or 11 according to concentration, equilibrium is rapidly re-established after such changes. At lower pH, equilibrium is approached more slowly, and changes in distribution with time can be followed.

Silicate species in solution. Part 2. The structure of polymeric species

The following rules are formulated concerning the structure of polymeric species in solution: (1) connectivity is maximised consistent with a lower ring size of four tetrahedra (except possibly in trimeric species); (2) all tetrahedra in a given species show as nearly as possible the same degree of connectivity. Both these rules are consistent with the idea that the lability of silicate groups in solution decreases with increasing connectivity.

Penta-co-ordinated aluminium: a solid-state 27Al, n.m.r. study

Penta-co-ordinated aluminates are shown to give 27Al n.m.r. chemical shifts of approximately 35 p.p.m. using solid-state n.m.r. spectroscopy.

Trimethylsilylation of linear and cyclic tetrameric silicates

The suppression of cyclisation side reactions during silicate derivatisation by the method of Tamas et al., using dimethylformamide as solvent, is demonstrated; the cyclic nature of the silicate skeleton in Pb2SiO4 is confirmed.

A penta-co-ordinated aluminate dimer; X-ray crystal structure

X-Ray structural analysis of a new barium aluminate glycolate (BaAlO8C6.75H14.75) has revealed a novel aluminate anion, formed from two distorted trigonal bipyramids sharing an edge to give a dimer.

Polymerisation of the silicate anion in acidic solutions. Gelation and trimethylsilylation studies

Trimethylsilylation studies on silicic acid solutions, produced by hydrolysis of tetramethoxysilane, show that gel time is independent of the rate of disappearance of monomeric silicic acid.

Trimethylsilyl derivatives for the study of silicate structures. Part III. Sodium silicate hydrates

A study was made of the yield and distribution of the products formed when Na2H2SiO4,4H2O, Na2H2SiO4,5H2O, and Na2H2SiO4,8H2O were treated by a direct method of trimethylsilylation reported previously. These soluble silicates are particularly prone to side reactions due to polymerisation of silicate ions in solution, yielding a distribution of products many of which are undetected chromatographically.Quantitative yields of the expected orthosilicate derivatives were obtained only when vanishingly small concentrations of silicate were used. Further experiments with the mineral hemimorphite confirmed that, for a unified method of trimethylsilylation applicable to different structures, careful control of the water content in the reaction medium is essential. Improvements in the trimethylsilylation and chromatographic procedures are described.