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Synthesis, characterization and computational studies of Boron-Oxygen compounds

Jones, Charlotte Louise (2016) Synthesis, characterization and computational studies of Boron-Oxygen compounds. PhD thesis, Prifysgol Bangor University.

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Abstract

A total of twenty-one new non-metal cation polyborate salts are reported; nineteen of these contain the pentaborate anion, [B5O6(OH)4]-, one contains the triborate monoanion, [B3O3(OH)4]-, and one contains the heptaborate dianion, [B7O9(OH)5]2-. The crystal structures of ten salts containing these polyborate anions are reported: pyrrolidinium pentaborate (1), N-methylpyrrolidinium pentaborate.½ acetone (2.½CH3COCH3), N,N-dimethylpyrrolidinium pentaborate (3), 2-hydroxymethylpyrrolidinium pentaborate hemihydrate (4.½H2O), (2-hydroxyethyl)-N-methylpyrrolidinium pentaborate.0.3 hydrate (5.0.3H2O), 4-aminobenzylammonium pentaborate hemihydrate (9.½H2O), N,N-dimethyl-1-adamantylammonium pentaborate sesquihydrate (14.1.5H2O), N,N,N-trimethyl-1-adamantylammonium pentaborate trihydrate (15.3H2O), N,N,N-trimethyl-2-adamantylammonium pentaborate trihydrate (17.3H2O) and 4,4’-bipiperidinium heptaborate dihydrate (20.2H2O). The crystal structure of an additional amine-boric acid co-crystallized species is also reported. All of the synthesized compounds reported in Chapter 3 were characterized using spectroscopic (IR, multi-element NMR) and analytical (melting point, elemental analysis, thermal analysis, powder X-ray diffraction) techniques. The solid-state structures of the polyborate salts form giant H-bonded anionic lattices, with the ‘brickwall’ structure found to be sufficiently flexible to accommodate larger cations (within limits). When these limits are approached, they may be stretched further to accommodate the size of the cations by using ‘spacer’ molecules which increase the size of the lattice. It is only once the lattice cannot be stretched any further and/or when there are sufficient cation-anion interactions to dominate the energetics that polyborates other than pentaborates may be observed. The strength of the H-bonds found within polyborate salts were calculated using DFT theory; the results show that the α-reciprocal R22(8) H-bond interaction is the most energetically favoured (-21 kJ mol-1), which is also the most commonly observed interaction within the solid-state structures of pentaborate salts. The synthesis and characterization of Lewis base adducts of triorganoboroxines is also described within this thesis. Eight new adducts are reported, including the crystal structures of the triorganoboroxine.amine adducts of tri(4-chlorophenyl)boroxine.morpholine (30) and tri(4-chlorophenyl)boroxine.benzylamine (33). The Lewis acidity of the triorganoboroxines were also investigated and it was discovered that strongly electron-withdrawing pentafluorophenyl substituents greatly increase the Lewis acidity of the B atoms, resulting in a higher acceptor number.

Item Type: Thesis (PhD)
Subjects: Degree Thesis
Departments: College of Physical and Applied Sciences > School of Chemistry
Degree Thesis
Date Deposited: 27 Jun 2017 08:13
Last Modified: 27 Jun 2017 08:13
URI: http://e.bangor.ac.uk/id/eprint/9875
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