Organometallic ionic liquids from alkyloctamethylferrocenium cations: thermal properties, crystal structures, and magnetic properties

Abstract

Alkyloctamethylferrocenium salts with the Tf2N anion ([Fe(C5Me4C(n)H(2n+1))(C5Me4H)][Tf2N]; Tf2N = bis(trifluoromethanesulfonyl)amide) were prepared, and their ionic liquid properties, thermal properties, crystal structures, and magnetic properties were investigated. The melting points of the Tf2N salts were near room temperature, and decreased with increasing alkyl chain length up to n = 8 and then increased. The salts with PF6 and NO3 anions were also prepared. The melting points of the PF6 salts were higher than 100 °C. Most of these salts exhibited phase transitions in the solid state. The sum of the entropies of the melting and solid phase transitions was nearly independent of the alkyl chain length for salts with short alkyl chains, whereas those for salts with longer alkyl chains (n≥ 10 for Tf2N salts, n≥ 6 for PF6 salts) increased with increasing alkyl chain length. Crystal structure determinations revealed that the short chain salts form simple alternately packed structures of cations and anions in the solid state, and that the long chain salts form lamellar structures, in which the alkyl chains are aligned parallel between the layers. The effects of magnetic fields on the crystallization of the paramagnetic ionic liquids were investigated, and revealed that the Tf2N salts with n = 4 exhibited magnetic orientation when solidified under magnetic fields. The magnetic orientation was shown to be a bulk phenomenon, and the importance of the magnetic anisotropy of the crystal structure was suggested in comparison with the response of other Tf2N salts.

Crystal Structures and Phase Sequences of Metallocenium Salts with Fluorinated Anions: Effects of Molecular Size and Symmetry on Phase Transitions to Ionic Plastic Crystals

“…[14] We previously found that alkylmetallocenium salts with Tf 2 Ng ave ionic liquids. [15] Therefore, an investigation of the phase transitions in theses alts bridges the gap in the understanding of organometallic ionic plastic crystalsa nd ionic liquids. Plastic phases have also been found in onium salts with the Tf 2 Na nion.…”

Effects of substituent branching and chirality on the physical properties of ionic liquids based on cationic ruthenium sandwich complexes

“…In [2][PF 6 ] and [3][PF 6 ], these short contacts appear between the ring hydrogens and the fluorine or oxygen atoms (CH arene Á Á ÁF), which are 0.2-0.3 Å shorter than the van der Waals contact distances. 18 6 ] in the high-temperature phase (vide ante), which thermodynamically stabilizes the solid phase. Such cation-anion interatomic contacts often appear in crystals of ionic liquids from sandwich complexes.…”

“…Therefore, the effects of molecular structure, such as the length of alkyl substituents, on the physical properties of ionic liquids have been extensively investigated. [17][18][19][20][21] We examine herein how substituent branching and chirality affect the thermal properties of organometallic ionic liquids. [4][5][6][7][8][9][10][11] Although most ionic liquids contain organic cations such as imidazolium cations, various metal-containing ionic liquids that exhibit intriguing functionalities have recently been developed.…”

Ionic liquids for addressing unmet needs in healthcare

“…Early advances were motivated to develop ILs as green, nonvolatile, nonflammable, and stable solvents, however, recent findings have broadened the field, redefining ILs as low melting salts (melting point <100°C) with an unlimited suite of tunable properties including toxicity, volatility, flammability, and instability . The erstwhile narrow perspective that views ILs as salts of quaternary ammonium, imidazolium, pyrrolidinium, pyridinium, or phosphonium cations has broadened as new cations including the bioinspired cholinium and guanidinium cations as well as metal‐containing cations are paired with various anions to afford salts that meet the definition of IL (Figure ). The evolving complexity of the precursors fosters a conjecture that explains their characteristically low melting point by the structural heterogeneity of a sterically hindered asymmetric cation that impedes strong ionic interaction with the anion as well as precludes ordered packing within a crystal lattice.…”