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Issue 14, 2012
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Halogen-free chelated orthoborate ionic liquids and organic ionic plastic crystals

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Abstract

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–H⋯π interaction. In the other salt, [EMIm][BScB], anions exhibit π⋯π stacking in combination with C–H⋯π 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.

Graphical abstract: Halogen-free chelated orthoborate ionic liquids and organic ionic plastic crystals

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Publication details

The article was received on 09 Jun 2011, accepted on 23 Jan 2012 and first published on 28 Feb 2012


Article type: Paper
DOI: 10.1039/C2JM12657E
Citation: J. Mater. Chem., 2012,22, 6928-6938
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    Halogen-free chelated orthoborate ionic liquids and organic ionic plastic crystals

    F. U. Shah, S. Glavatskih, P. M. Dean, D. R. MacFarlane, M. Forsyth and O. N. Antzutkin, J. Mater. Chem., 2012, 22, 6928
    DOI: 10.1039/C2JM12657E

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