Ferromagnetically coupled CoII2LnIII2 complexes (where LnIII = Ho, Er, Yb): experimental and theoretical investigations

Abstract

A series of heterotetranuclear complexes [Co^II₂Ln₂(HL)₄(OAc)₃(H₂O)₂]·(NO₃)₃ (where Ln^III = Ho (1), Er (2) or Yb (3)) reported with a Schiff base (2-methoxy-6-[(E)-2′-hydroxymethyl-phenyliminomethyl]-phenol) ligand. The X-ray diffraction and structural solution confirmed the isostructural identity of 1 and 3. Complexes 1 and 3 were crystallized in a monoclinic crystal system having a C2/c space group, while complex 2 lacked X-ray quality crystals. The direct current (dc) magnetic measurements on complexes 1–3 indicate dominant intramolecular ferromagnetic interactions. The CASSCF/SO-RASSI/SINGLE_ANISO calculations followed by POLY_ANISO simulations were performed to understand the electronic structure, nature and strength of the Co^II–Ln^III and Ln^III–Ln^III magnetic exchange interactions, using the Molcas 8.0 program. To verify the nature of Co^II–Ln^III magnetic interactions, BS-DFT calculations were performed. The sign and the magnitude of the estimated J_Co–Ln values show weak but dominant intramolecular ferromagnetic interactions between Co^II and Ln^III metal ions. In contrast, J_Ln–Ln values show the weak antiferromagnetic interactions between Ln^III ions in complexes 1–3.