Structural and thermal studies of non-metal cation pentaborate salts with cations derived from 1,5-diazobicyclo[4.3.0]non-5-ene, 1,8-diazobicyclo[5.4.0]undec-7-ene and 1,8-bis(dimethylamino)naphthalene

The reaction of the cyclic amines 1,5-diazobicyclo[4.3.0]non-5-ene (DBN), 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) and 1,8-bis(dimethylamino)naphthalene (PS) with B(OH)3 in a 1:5 ratio affords in high yields the non-metal cation pentaborate salts [HDBN][B5O6(OH)4] (1), [HDBU][B5O6(OH)4] (2) and [HPS][B5O6(OH)4]·B(OH)3 (3). Compounds 1–3 were characterized by spectroscopic studies (NMR, IR) and compounds 1 and 3 were further characterized by single-crystal XRD studies. The pentaborate salts compounds show extensively H-bonded supramolecular anionic lattices which are templated by the cations. Thermal analysis (TGA) of 1–3 showed that thermally decomposed in air at 1000° to B2O3 in a two step process involving dehydration (<250 °C) and oxidation (250–600 °C). BET analysis of materials derived from thermolysis of 1–3 had internal porosities of <1 m2/g.

Graphical abstractThe cation originating from protonated 1,8-bis(dimethylamino)naphthalene (PS) is accommodated within the supramolecular H-bonded pentaborate anionic lattice of [PSH][B5O6(OH)4]·B(OH)3 by the inclusion of H-bonded B(OH)3 ‘spacer’ molecules.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Three new non-metal cation pentaborate salts of have been synthesised. ► Solid-state structures (XRD) show H-bonded supramolecular anionic lattices. ► TGA analysis showed that these salts thermally decompose in air to B2O3. ► BET analysis of thermally derived materials had porosities of <1 m2/g.