A series of six-membered lanthanide rings based on 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol: synthesis, crystal structures and magnetic properties

Abstract

By utilizing a solvothermal method, a series of six-membered cyclic lanthanide(III) clusters, {Gd₆(H₃L)₆(benzoate)₆}·2H₂O·C₇H₈ (1), {Tb₆(H₃L)₆(benzoate)₆}·2H₂O·C₇H₈ (2) and {Dy₆(H₃L)₆(benzoate)₆}·2H₂O (3), have been constructed with the pentol ligand, 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (H₅L). Similar hexa-nuclear ring structures were observed in each of the crystal structures. In addition, magnetization studies indicated that Gd₆ displays large magnetic entropy changes in low temperature regions. What is particularly interesting about this ring is the presence of slow magnetic relaxation behavior under a zero dc field, indicating a non-magnetic ground state with a net toroidal magnetic moment. Compared to the other reported Dy₆ clusters, modulation of the ligand fields, the presence of amine coordinating sites and the subsequent electron density of the Dy centers along with the utilized pentol ligand might be indeed responsible for the improved barrier to magnetic relaxation.