Photoluminescent and Magnetic Properties of Mononuclear Lanthanide-Based Compounds Containing the Zwitterionic Form of 4-Picolinic Acid as a Ligand

A series of mononuclear lanthanide-based coordination compounds was obtained under mild synthetic conditions and fully characterized. Single-crystal X-ray diffraction reveals six isomorphic compounds of type [Ln(NO3)(4picH)2(H2O)4](NO3)2 (Ln3+ = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Er (6)), in which 4picH is the zwitterionic form of the 4-picolinic acid. Except for compounds 3 and 6, a study into the emissive properties of the compounds was carried out, revealing a ligand-sensitized lanthanide-characteristic luminescence. Compounds 2 and 4 are candidates for luminescent probes in solution. At the same time, the chromaticity data for 5 revealed a potential white-light emitter with a correlated color temperature (CCT) value of 6570 K. Alternating current (AC) magnetic susceptibility measurements, supported by theoretical calculations, showed a fieldinduced slow relaxation of the magnetization and a single-ion magnet behavior for compound 5.