Incommensurate crystal structure, thermal expansion study and magnetic properties of (dimethylimidazolium)₂[Fe₂Cl₆(μ-O)]

Abstract

A thorough characterization of the title compound, (dimim) 2 [Fe 2 Cl 6 (μ-O)], consisting of a (μ-oxido)-bridged binuclear iron(III) complex and 1,3-dimethylimiazolium (dimim) cation, has been performed using a wide range of techniques. The room temperature disordered crystal structure of this compound transits to an incommensurately modulated crystal structure at 100 K; to our knowledge, the first one found for an imidazolium halometallate complex. The crystal structure was solved in the superspace group P1(/α/β/γ)0 with modulation vector q=0.1370(10) 0.0982 (10) 0.326(2) at 100 K. Variable temperature synchrotron powder x-ray diffraction showed the presence of satellite peaks in addition to the main diffraction peaks up to 208 K. Furthermore, a thermal expansion study was performed with this technique from 100 to 383 K (near of its melting point) adressing questions about the nature and consequences of the ion self-assembly of this (μoxido)-bridged binuclear iron(III) complex, as well as the molecular motion of the imidazolium cation within the crystalline structure as a response to the temperature effect. Finally, we present a deep magnetic study based on magnetic susceptibility, magnetization and Mössbauer measurements, where the strong antiferromagnetic exchange coupling detected is due to the occurrence of a μ-oxido bridge between the Fe(III), giving rise to an intra-dimeric antiferromagnetic exchange coupling of -308 cm −1 .

Crystal structure, magneto-structural correlation, thermal and electrical studies of an imidazolium halometallate molten salt: (trimim)[FeCl4]

“…1), in good agreement with those obtained from DSC. These transitions are related to a change in the molecular conformation of the crystal structure and are associated to the ionic mobility of the imidazolium cation, 25,26 as it will be discussed below and in the electrochemical impedance spectroscopy (EIS) section.…”

Crystal and magnetic structure of the (trimim)[FeBr4] molten salt: A temperature dependence study

“…These disorders are common for this type of complexes and are related to the ionic mobility of the imidazolium cation due to the weak forces that build up the structure. [22,23] We can observe the weak character of this transition in the DSC analysis (Fig. S4, SI) where a small bump at 350 K appears, in comparison to the marked peak associated to the melting process.…”