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Halogen-free chelated orthoborate ionic liquids and organic ionic plastic crystals

journal contribution
posted on 14.04.2012, 00:00 authored by F Shah, S Glavatskih, P Dean, D MacFarlane, Maria ForsythMaria Forsyth, O Antzutkin
Five halogen-free orthoborate salts comprised of three different cations (cholinium, pyrrolidinium and imidazolium) and two orthoborate anions, bis(mandelato)borate and bis(salicylato)borate, were synthesised and characterised by DSC, X-ray diffraction and NMR. DSC measurements revealed that glass transition points of these orthoborate salts are in the temperature range from −18 to −2 °C. In addition, it was found that [EMPy][BScB] and [EMIm][BScB] salts have solid–solid phase transitions below their melting points, i.e. they exhibit typical features of plastic crystals. Salts of the bis(salicylato)borate anion [BScB]− have higher melting points compared with corresponding salts of the bis(mandelato)borate anion [BMB]−. Single crystal X-ray diffraction crystallography (for [Chol][BScB] crystals) and solid-state multinuclear (13C, 11B and 15N) NMR spectroscopy were employed for the structural characterisation of [Chol][BScB], [EMPy][BScB] and [EMIm][BScB], which are solids at room temperature: a strong interaction between [BScB]− anions and [Chol]+ cations was identified as (i) hydrogen bonding between OH of [Chol]+ and carbonyl groups of [BScB]− and (ii) as the inductive C–Hπ interaction. In the other salt, [EMIm][BScB], anions exhibit ππ stacking in combination with C–Hπ interactions with [EMIm]+ cations. These interactions were not identified in [EMPy][BScB] probably because of the lack of aromaticity in cations of the latter system. Our data on the formation of a lanthanum complex with bis(salicylato)borate in the liquid mixture of La3+(aq) with [Chol][BScB] suggest that this class of novel ILs can be potentially used in the extraction processes of metal ions of rare earth elements.

History

Journal

Journal of materials chemistry

Volume

22

Issue

14

Pagination

6928 - 6938

Publisher

Royal Society of Chemistry

Location

Cambridge, England

ISSN

0959-9428

eISSN

1364-5501

Language

eng

Publication classification

C1 Refereed article in a scholarly journal