Synthesis, structure and near-infrared photoluminescence of hexanitratoneodymate ionic liquids

Abstract

Five hexanitratoneodymate-based rare earth complexes (1–5) were synthesized using a straightforward method. Purple plate crystals of 1 were isolated and the crystal structure was determined by single-crystal X-ray diffraction with respect to the coordination mode of the nitrate anion to the central Nd(III) ion. (1: monoclinic system P2₁/c, a = 15.9460(3) Å, b = 10.2457(6) Å, c = 33.323(3) Å, β = 91.8108(17)°, V = 3109.11(11) ų, Z = 4). The central Nd(III) ion is surrounded by six bidentate nitrate ligands, with a major trend towards high symmetry of the [Nd(NO₃)₆]³⁻ anion as an icosahedron. Thermal properties were determined from differential scanning calorimetry (DSC) combined with thermogravimetric analysis (TGA) tests. Complexes 3–5 are found to be room temperature liquids, and their excitation and emission spectra were recorded. These complexes exhibit intense near-infrared (NIR) luminescence emission, which originates from interconfigurational f–f transitions ⁴F_3/2→⁴I_J multiplet (J = 9/2–13/2). These liquid Nd(III) complexes are of interest as potential NIR luminescent soft materials with high thermal stability.