2-Formylphenoxyacetic acid Schiff bases: a promising ligand scaffold for readily available trigonal prismatic Co(ii) single-ion magnets

Abstract

This article presents a series of six mononuclear Co(II) complexes 1–6 featuring ligands derived from a hexadentate Schiff base family, originating from the condensation of (2-formylphenoxy)acetic acid with various diamines. Notably, these complexes uniquely prefer a trigonal prism geometry, presenting a novel approach to synthesizing complexes with this distinctive shape. The compounds were characterized by elemental analysis, FT-IR spectroscopy, and single-crystal and powder XRD techniques. Furthermore, the magnetism was investigated by DC and AC magnetic measurements and also complemented by X-band EPR spectroscopy. The results reveal that the prepared complexes behave as field-induced single-molecule magnets, characterized by a substantial negative axial zero-field splitting D-parameter and spin reversal energetic barrier U_eff reaching values up to 72 K. The theoretical methods based on CASSCF/NEVPT2 calculations were applied to rationalize their magnetic properties. Moreover, these complexes hold promising potential for further functionalization, offering opportunities to enhance their properties, particularly towards developing zero-field single-molecule magnets as evidenced by the slow relaxation of magnetization in zero static magnetic field observed for the zinc-diluted complex 1Zn.