Low-melting multicharge ionic liquids with [Ln(NO3)5]2- (Ln = Ho-Lu): structural, electrostatic, thermochemical, and fluorescence properties.

A series of green and safe heavy-rare-earth ionic liquids were obtained using a straightforward method. The stable structures of these ionic liquids, characterized by high-coordinating anions, were confirmed by nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and single crystal X-ray diffraction (XRD). These ionic liquids exhibited wide liquid phase intervals and excellent thermal stability. The bidentate nitrato ligands occupied a sufficient number of coordination sites on the lanthanide ions, resulting in the formation of water-free 10-coordination structures. To explain the anomalous melting points observed in these multi-charged ionic liquids, a combination of experimental data and theoretical studies was employed to investigate the relationship between the electrostatic properties and the melting point. The electrostatic potential density per unit ion surface and volume were proposed and utilized for melting point prediction, demonstrating good linearity. Furthermore, the coordinating spheres of the lanthanide ions in these ionic liquids were devoid of luminescence quenchers such as O-H and N-H groups. Notably, the ionic liquids containing Ho3+, Er3+, and Tm3+ exhibited long lifetime near-infrared (NIR) and blue emissions, respectively. The UV-vis-NIR spectra revealed numerous electronic transitions of the lanthanide ions, which were attributed to their unique optical properties.

Fluorescigenic Magnetofluids Based on Gadolinium, Terbium, and Dysprosium-Containing Imidazolium Salts.

Multistimuli responsive soft materials are urgently needed in many different fields, such as anticounterfeiting technology and microdroplet manipulation. Herein, the straightforward preparation of fluorescigenic magnetofluids by the introduction of the paramagnetic metal ions Gd3+, Tb3+, and Dy3+ into alkylimidazolium-based ionic liquids (ILs) is reported. Bright visible fluorescence was observed under UV irradiation for Tb- and Dy-containing ILs. Either pure samples or papers coated with these ILs exhibited pronounced magnetic responses. Consistent and stable structures of these salts were confirmed by systematical characterizations. Because of the competition of nitrate ligands, structural water in the precursors was eliminated easily under a vacuum. For Tb- and Dy-containing ILs, featured electronic transitions were observed and were assigned in the fluorescence spectra. The long lifetimes of these transitions were also confirmed. The field-cooling experiments showed that all of these ILs display paramagnetism at room temperature. At low temperature, small deviations from the Curie Law indicate the occurrence of antiferromagnetic coupling and spin canting in these ILs. Temperature-induced differences in magnetic properties were further verified by field-dependent magnetic susceptibility measurements carried out at 5 and 300 K.