A new series of 3D lanthanide phenoxycarboxylates: synthesis, crystal structure, magnetism and photoluminescence studies

Abstract

A new series of 3D lanthanide (Ln) frameworks has been synthesized with the general formula [{Ln(L)(H₂O)}·H₂O]_n (where Ln = La(1), Tb(2) and Dy(3); L = (HO)OC₆H₂(CH₂COO)₂; H₃L = 2,5-dihydroxy-1,4-benzenediacetic acid = DHBDA). All the crystals were analyzed by single crystal X-ray diffraction. The Ln ions are octa-coordinated having the square antiprism geometry with the D_4d symmetry and connected along the crystallographic a-axis forming a zigzag chain. These chains are further connected by the ligands in three-dimensional crystallographic space. Compounds 2 and 3 were subjected to variable temperature magnetic susceptibility measurements and photoluminescence studies. Magnetic studies reveal that compound 2 possesses antiferromagnetic coupling whereas compound 3 shows ferromagnetic interaction at temperatures above ca. 40 K. The emission spectra of compounds 2 and 3 combine the intra-4f emission of the Ln ions with that of the ligand, depending on the selected temperature, pointing out that the energy transfer processes are thermally activated. In addition, compound 2 presented an invariant ⁵D₄ lifetime behaviour at temperatures between 15 and 300 K. Theoretical analysis showed that the long-lived lifetimes of the free ligand's excited states and the intramolecular energy transfer rate invariability are responsible for such abnormal behaviour.