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

A new series of 3D lanthanide (Ln) frameworks has been synthesized with the general formula [{Ln( L )(H 2 O)}·H 2 O] n (where Ln = La( 1 ), Tb( 2 ) and Dy( 3 ); L = (HO)OC 6 H 2 (CH 2 COO) 2 ; H 3 L = 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 5 D 4 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. A new series of 3D Ln-carboxylates was synthesized, where the Tb one shows antiferromagnetic coupling and the Dy one shows ferromagnetic interaction, and with emission spectra combining the intra-4f emission of the Ln ions and that of the ligand.