Crystal structure, magneto-structural correlation, thermal and electrical studies of an imidazolium halometallate molten salt: (trimim)[FeCl4]. Issue 19 (23rd March 2020)

• Record Type: Journal Article
• Authors: González-Izquierdo, Palmerina; Fabelo, Oscar; Beobide, Garikoitz; Cano, Israel; Ruiz de Larramendi, Idoia; Vallcorba, Oriol; Fernández, Jesús Rodríguez; Fernández-Díaz, María Teresa; de Pedro, Imanol
• Is Part Of: RSC advances. Volume 10:Issue 19(2020)
• Page Start: 11200
• Page End: 11209
• Publication Date: 2020-03-23
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra00245c
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : We present a novel halometallate molten salt based on imidazolium cation with two structural transitions from 100 to 400 K which has been studied by X-ray and neutron diffraction techniques. Furthermore, the magnetic structure at low temperature and the ionic conductivity is also described. Abstract : A novel imidazolium halometallate molten salt with formula (trimim)[FeCl4 ] (trimim: 1, 2, 3-trimethylimidazolium) was synthetized and studied with structural and physico-chemical characterization. Variable-temperature synchrotron X-ray powder diffraction (SXPD) from 100 to 400 K revealed two structural transitions at 200 and 300 K. Three different crystal structures were determined combining single crystal X-ray diffraction (SCXD), neutron powder diffraction (NPD), and SXPD. From 100 to 200 K, the compound exhibits a monoclinic crystal structure with space group P 21 / c . At 200 K, the former crystal system and space group are retained, but a disorder in the organic cations is introduced. Above 300 K, the structure transits to the orthorhombic space group Pbcn, retaining the crystallinity up to 400 K. The study of the thermal expansion process in this temperature range showed anisotropically evolving cell parameters with an axial negative thermal expansion. Such an induction occurs immediately after the crystal phase transition due to the translational and reorientational dynamic displacements of the imidazolium cation within the crystal building. Electrochemical impedance spectroscopy (EIS) demonstrated that this motion implies a high and stable solid-state ionic conduction (range from 4 × 10 −6 S cm −1 at room temperature to 5.5 × 10 −5 S cm −1 at 400 K). In addition, magnetization and heat capacity measurements proved the presence of a three-dimensional antiferromagnetic ordering below 3 K. The magnetic structure, determined by neutron powder diffraction, corresponds to ferromagnetic chains along the a -axis, which are antiferromagnetically coupled to the nearest neighboring chains through an intricate network of superexchange pathways, in agreement with the magnetometry measurements.