Compartmental ligand approach for constructing 3d–4f heterometallic [CuII5LnIII2] clusters: synthesis and magnetostructural properties

Abstract

The employment of a reduced Schiff-base ligand, 1,3-bis(3-methoxy-salicylamino)-2-propanol (H₃L), with the assistance of acetate anions led to the isolation of eight heptanuclear heterometallic complexes containing [Cu₅Ln₂] cores. Single-crystal X-ray diffraction analyses have been performed for all the complexes and show that they all have dicationic [Cu₅Ln₂] cores with two nitrate or hexafluorophosphate anions to compensate the charge. The dicationic parts in 1–8 display centrosymmetric hexagonal-like arrangements in which one Cu^II ion sits on the inversion centre with six peripheral metal ions (two Ln^III and four Cu^II) around it. The magnetic susceptibilities of all the complexes have been studied by dc magnetic measurements. The temperature dependent magnetic susceptibility data for the Cu^II–Gd^III complex have been processed using PHI software. The results reveal that the magnetic exchange interactions between Cu^II and Cu^II ions are antiferromagnetic while those between Cu^II and Gd^III ions are ferromagnetic. The magnetostructural correlations reveal that the bridging angles of Cu–O–Cu and Cu–O–Gd greatly influence the magnetic coupling of Cu^II–Cu^II and Cu^II–Gd^III, respectively. Further, ac susceptibility studies have been carried out for Dy^III and Tb^III complexes and Ho^III derivatives. The complexes Cu^II–Ho^III and Cu^II–Tb^III show slow magnetization relaxation behaviour of an SMM.