Dynamically slow solid-to-solid phase transition induced by thermal treatment of DimimFeCl₄ magnetic ionic liquid

Abstract

The results reported here represent the first direct experimental observations supporting the existence of a solid-to-solid phase transition induced by thermal treatment in magnetic ionic liquids (MILs). The phase transitions of the solid phases of 1,3-dimethylimidazolium tetrachloroferrate, DimimFeCl4, are closely related to its thermal history. Two series of solid-to-solid phase transitions can be described in this MIL: (i) from room temperature (RT) phase II [space group (s.g.) = P21] to phase I-a [s.g. = P212121] via thermal quenching or via fast cooling at T > 2 K min(-1); (ii) from phase I-a to phase I-b [s.g. = P21/c] when the temperature was kept above 180 K for several minutes. The latter involves a slow translational and reorientational dynamical process of both the imidazolium cation and the tetrachloroferrate anion and has been characterized using synchrotron and neutron powder diffraction and DFT (density functional theory) studies. The transition is also related to the modification of the super-exchange pathways of low-temperature phases which show a overall antiferromagnetic behavior. A combination of several experimental methods such as magnetometry, Mössbauer and muon spectroscopy together with polarized and non-polarized neutron powder diffraction has been used in order to characterize the different features observed in these phases.

An Oxalate‐Bridged Binuclear Iron(III) Ionic Liquid for the Highly Efficient Glycolysis of Polyethylene Terephthalate under Microwave Irradiation

“…20 K. The inverse of the magnetic susceptibility data can be fitted to a Curie‐Weiss law (red line in Figure ) with paramagnetic Curie temperatures (θ p ) close to 44 K and an effective paramagnetic moment μ eff =10.68 μ B /molecule. The latter is consistent with the value expected for two Fe 3+ ions with high spin d 5 configuration (μ eff =5.92 μ B /Fe ion) and is in a good agreement with that found for other Fe(III)‐based halometallate ions . In addition, the negative θ p value and the reduction of the effective magnetic moment (χ m T) with the decrease of temperature (see upper inset Figure ) clearly suggest an antiferromagnetic behavior when cooling the sample.…”

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

“…Among them, tetrahaloferrate(III) complexes are particularly attractive due to their magnetic and crystal behavior. 12,13 Specically, imidazolium-based tetrahaloferrate(III) compounds present long-range magnetic order at low temperature [14][15][16][17] which lead to a highly organized 3-D structure in their condensed phase. Different types of interactions build up their crystal structure, from nonspecic isotropic forces, weak (like van der Waals, solvophobic and dispersion forces) and strong (coulombic), to specic anisotropic forces (such as hydrogen bonding, halogen bonding, dipole-dipole, magnetic dipole and electron pair donor/acceptor interactions).…”

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

“…The structural characterization of the complex was also performed by Raman spectroscopy, as this technique offers one of the most rewarding and simple means for studying the bonding and type of anionic species in halometallate compounds in a lab [4][5][6][7][8][9]. Figure 8 shows the non-polarized Raman spectra of (dimim) 2 [Fe 2 Cl 6 (μ-O)] and (dimim)[FeCl 4 ] (for the comparison), between 50 and 3200 cm −1 at 300 K with 647 nm excitation.…”

“…In addition, they possess a latent acidity (the presence of water causes shifts in anion equilibrium) comparable to those containing chloroaluminates. Taking advantage of this acidity, moisture stability, Fe and Cl abundance, ability to dissolve a wide range of organic compounds and magnetic properties [4][5][6][7][8], chloroferrate(III) complexes show many applications [9]. They are especially useful as catalysts for a wide variety of transformations including glycosidation [10], Michael addition [11], desulfurization [12], CO 2 fixation into cyclic carbonates [13], Friedel Crafts acylation [14], for benzylation of various arenes/heteroarenes into the diarylmethanes [15], for Lewis rechargeable batteries [16] or glycolysis of polyethylene terephthalate (PET) waste [17,18].…”

“…Concretely, these complexes based on imidazolium cation display a wide variety of interactions, ranging from nonspecific and isotropic forces, weak ones (e.g., van der Waals (vdW), solvophobic, dispersion forces) and strong ones (Coulombic), to specific and anisotropic forces (e.g., hydrogen bonding, halogen bonding, dipole−dipole, magnetic dipole, electron pair donor/acceptor interactions). The competition among the aforementioned interactions could drive to structural phase transitions as observed in neutral chloroferrate(III) complexes, mainly due to order-disorder phenomena or the libration of the imidazolium cation [3][4][5][6][7][8].…”