3‑Pyridylacetic-Based Lanthanide Complexes Exhibiting Magnetic Entropy Changes, Single-Molecule Magnet, and Fluorescence

Four complexes from lanthanides, 3-pyridylacetate, and 1,10-phenanthroline, formulated as [Ln2(3-PAA)2(μ-Cl)2(phen)4]­(ClO4)2 [Ln = Gd­(1), Dy­(2), Eu­(3), Tb­(4), 3-PAA = 3-pyridylacetic acid, phen = 1,10-phenanthroline], were obtained. The four compounds were characterized by IR spectra, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1–4 are isomorphous, and they have a dinuclear structure. Magnetic studies reveal that 1 shows the magnetocaloric effect with −ΔSmmax = 19.03 J kg–1 K–1 at 2 K for ΔH = 5 T, and 2 displays a field-induced single-molecule magnet with Ueff = 19.02 K. The photoluminescent spectra of 3 and 4 exhibit strong characteristic emission, which demonstrate that the ligand-to-EuIII/TbIII energy transfer is efficient.