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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Crystallisation of inorganic salts containing 18-crown-6 from ionic liquids
Ning Yan a,b, Zhaofu Fei a, Rosario Scopelliti a, Gàbor Laurenczy a, Yuan Kou b, Paul J. Dyson a,*
Institut des Sciences et Ingénierie Chimiques,Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland PKU Green Chemistry Center, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China
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Reaction of the zwitterionic imidazolium salt [(CH2COOH)(CH2COO)im] with K2CO3 or BaO in the presence of18-crown-6 affords the salts [(CH2COO)2im][K(18-crown-6)] and [(CH2COO)2im]2[Ba(18crown-6)], respectively. Recrystallisation of these crown complexes from the ionic liquid 1-ethyl-3-methylimidazolium bis(triﬂuoromethylsulfonyl)amide, [emim][Tf2N], at a water interface, results in the formation of new salts in which the original anion is replaced by Tf2NÀ. Single crystal X-ray diffraction has beenperformed on two of the salts. Notably, the potassium structure containing 18-crown-6 and Tf2NÀ forms a linear chain coordination polymer that can be regarded as metal organic frameworks (MOFs). Moreover, this study provides insights into the separation of group I and II metal ions using crown ethers in combination with ionic liquids. Ó 2009 Elsevier B.V. All rights reserved.
Article history:Received 5 January 2009 Received in revised form 28 May 2009 Accepted 6 June 2009 Available online 18 June 2009 Dedicated to Prof. Paul Pregosin on the occasion of his 65th birthday in recognition of his many seminal contributions to chemistry, including ionic liquids. Keywords: Ionic liquids (ILs) Crystallisation X-ray crystallography Metal organic frameworks Coordination polymers ZwitterionsCrown ethers
1. Introduction Ionic liquids (ILs) are non-volatile solvents that have been extensively studied in synthesis and catalysis [1–4]. Many ILs are non-coordinating or weakly coordinating which endows them with potentially interesting properties for the synthesis of inorganic (metal containing) compounds and materials  such as transition metal complexes [6,7] and coordination polymers. For example, in a coordination polymer isolated from the reaction of Cu(NO3)2Á3H2O and 1,3-bis(4-pyridyl)propane in 1-butyl-3methylimidazolium tetraﬂuoroborate, [bmim][BF4], the cations and anions of the IL do not interact directly with the Cu-centres, although the tetraﬂuoroborate anions are maintained in the macrostructure in order to balance the charge. More recently it has been found ILscomprising the Tf2N anion may coordinate to metals via the O, N and S atoms in various chelating bonding-modes [9–11]. Indeed, the coordinating ability of ILs has led to many interesting applications . Imidazoliumbased ILs can be used as solvents for the separation of radioactive materials such as UO22+ . Europium-based ILs and dysprosiumbased ILs can be used as soft luminescent materials[14,15].
* Corresponding author. E-mail addresses: zhaofu.fei@epﬂ.ch (Z. Fei), paul.dyson@epﬂ.ch (P.J. Dyson). 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.06.020
It has also been shown that ILs can be used to separate group I and II metals in combination with crown ethers [16–18]. The mechanism of the separation process is believed toinvolve cocrystallisation of the imidazolium-based salts with 18-crown-6 containing metal ions , and the driving force for the inclusion of neutral 18-crown-6 ether into the packing of the imidazolium salts appears to be due to non-covalent interactions such as hydrogen bonding, p-stacking and electrostatic interactions . It is worth noting that functionalized ILs in which an 18-crown-6...
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