Halogen-free chelated orthoborate ionic liquids and organic ionic plastic crystals
2012 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 14, 6928-6938 p.Article in journal (Refereed) Published
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 degrees 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 (C-13, B-11 and N-15) 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 center dot center dot center dot pi interaction. In the other salt, [EMIm][BScB], anions exhibit pi center dot center dot center dot pi stacking in combination with C-H center dot center dot center dot pi 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.
Place, publisher, year, edition, pages
2012. Vol. 22, no 14, 6928-6938 p.
IdentifiersURN: urn:nbn:se:kth:diva-89270DOI: 10.1039/c2jm12657eISI: 000301459500058ScopusID: 2-s2.0-84858718618OAI: oai:DiVA.org:kth-89270DiVA: diva2:502903
QC 201205022012-02-142012-02-142012-05-02Bibliographically approved