Structural (XRD) and thermal (DSC, TGA) and BET analysis of materials derived from non-metal cation pentaborate salts

Beckett, Michael A., Horton, Peter N., Hursthouse, Michael B., Knox, David A. and Timmis, James L. (2010) Structural (XRD) and thermal (DSC, TGA) and BET analysis of materials derived from non-metal cation pentaborate salts. Dalton Transactions, 39 (16), 3944-3951. (doi:10.1039/b927072h). (PMID:20372719)

Abstract

The synthesis, structural characterization (XRD), and thermal properties of nine non-metal cation (NMC) pentaborate anion salts, [NMC][B5O6(OH)(4)] (1a-1i) is described (NMC = [NH3CMe2(CH2OH)](+) (a), [O(CH2CH2)(2)NH2](+) (b), [NH3CMe(CH2OH)(2)](+) (c), [2-(2-CH2CH2OH)PyH](+) (d), [(CH2)(4)NH(CH2CH2OH)](+) (e), [(CH2)(5)NH(CH2CH2OH)](+) (f), [2-MeImid](+) (g), [Me3NCMe2(CH2OH)](+) (h), [O(CH2CH2)(2)NMe2](+) (i). Single-crystal X-ray diffraction studies on all compounds show that they contain isolated pentaborate anions, H-bonded together in a supramolecular array, with the cations occupying the cavities within the network. Compound 1c was obtained as a partial hydrate (0.16H(2)O). TGA and DSC analysis ( in air, 25-1000 degrees C) indicate that compounds 1a-1i thermally decompose via a 2 stage process to B2O3. The. first stage (<250 degrees C) is dehydration to condensed polymeric pentaborates {approximate composition: [NMC][B5O8] (2a-2i)}. Five condensed pentaborates (2a-c, 2e, 2g) were synthesised and characterized by powder XRD and BET analysis. These condensed pentaborates were amorphous. The isolated pentaborates intumesced at similar to 600 degrees C ( occupying similar to 10 times their original volume), and then contracted back to black glassy B2O3 solids at 1000 degrees C. The intumescent materials (3a), (3b), (3e), (3g), and a. final B2O3 sample (4b) were synthesised and isolated and their porosities determined. BET surface area analysis on the isolated pentaborates (1a-c, 1e, 1g), the condensed pentaborates (2a-c, 2e, 2g), intumesced materials (3a, 3b, 3e, 3g), and B2O3 (4b) showed that they were all 'non-porous' (<1.59 m(2) g(-1))

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Contributors

Author: Peter N. Horton

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