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Issue 16, 2010
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Structural (XRD) and thermal (DSC, TGA) and BET analysis of materials derived from non-metal cation pentaborate salts

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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)2NH2]+ (b), [NH3CMe(CH2OH)2]+ (c), [2-(2-CH2CH2OH)PyH]+ (d), [(CH2)4NH(CH2CH2OH)]+ (e), [(CH2)5NH(CH2CH2OH)]+ (f), [2-MeImid]+ (g), [Me3NCMe2(CH2OH)]+ (h), [O(CH2CH2)2NMe2]+ (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 (0.16H2O). TGA and DSC analysis (in air, 25–1000 °C) indicate that compounds 1a–1i thermally decompose via a 2 stage process to B2O3. The first stage (<250 °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 ∼600 °C (occupying ∼10 times their original volume), and then contracted back to black glassy B2O3 solids at 1000 °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 m2 g−1).

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

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Publication details

The article was received on 24 Dec 2009, accepted on 17 Feb 2010 and first published on 11 Mar 2010


Article type: Paper
DOI: 10.1039/B927072H
Citation: Dalton Trans., 2010,39, 3944-3951
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    Structural (XRD) and thermal (DSC, TGA) and BET analysis of materials derived from non-metal cation pentaborate salts

    M. A. Beckett, P. N. Horton, M. B. Hursthouse, D. A. Knox and J. L. Timmis, Dalton Trans., 2010, 39, 3944
    DOI: 10.1039/B927072H

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