NMR studies of borate and silicate systems involving Na / TAA cations.

Abstract

The preparation and analysis of borate species (using 11B NMR) within a
series of previously unreported aqueous T AA borate solutions is described. The TAA cations took the form [R3NCH2CH(OH)CH20 Ht { where R = CH3, CH2CH3,
CH2CH20H, CH2C6H5 and CH2CH(OH)CH20H}; the resultant borate solutions were found to contain both neutral and cationic borate species. Three new pentaborate compounds [C10H6(N(CH3)2)2H][Bs06(0CH3)4], [(CH3)3NCH2CH20H][Bs0 6(0H)4] and [4-CH3C5H4N, 4-CH3C5H4NH][Bs06(0H)4), have been prepared and their structures determined by single crystal XRD studies. Aqueous silicate solutions containing either new T AA cations or T AA borate ester complexes have been prepared. The influence of the cation upon silicate speciation was monitored using 29Si NMR spectroscopy. It was found that the 1,2-dihydroxy-functionalised TAA cations (i.e. [R3NCH2CH(OH)CH20Ht) lost
their structure directing control over the silicate anion distribution upon chelation of the ortho-borate anion by the 1,2-diol moiety of the cation.
The co-condensation of organotrihydroxysilanes and silicate aruons m aqueous solution has also been investigated. Attempts (by 2D 29Si - 29 Si COSY
NMR) to provide conclusive evidence for the formation of Si-0-Si linkages between the r and Q11 units were unsuccessful. The incorporation of ortho-borate anions and metal cations into an aqueous sodium silicate solution utilising preformed organotrialkoxysilane complexes is also described. [B(OH)4r was chelated by 1,2-dihydroxy-functionalised organotrihydroxysilane derivatives, whilst the metal ions (e.g. Sn2+, Pb2+, Zn2+) were introduced with a EDTA-substituted organotrihydroxysilane.
The drying of an aqueous sodium silicate solution has been investigated. A
combination of solution and solid-state 29 Si NMR techniques demonstrated that
dehydration of the solution led to an increase in the extent of cross-linking between Q11 silicate units.

Date of Award	Mar 2007
Original language	English
Awarding Institution	University of Wales, Bangor
Sponsors	PILKINGTON GROUP LTD
Supervisor	Mike Beckett (Supervisor)