Enhancement of the coordinating flexibility in a Schiff–Mannich combo ligand: forced generation of a new NiII–Ophenoxo–LnIII–Oalkoxo–LnIII array (Ln = Gd, Tb, Dy and Ho)

Abstract

3d–4f coordination complexes derived from appropriately designed ligand backbones offer great perspectives to construct functional magnetic materials. Here we have reported a ligand design strategy by introducing flexible ethanol amine arms in a conventional salen type ligand by Schiff base and Mannich reaction and shown how this Schiff–Mannich combo ligand approach afforded a series of Ni^IILn^III₂ (Ln = Gd, Tb, Dy and Ho) complexes. We have reacted the ligand with Ni^II to generate a metalloligand and by means of secondary assembly of this metalloligand with Ln^III salts, the above mentioned Ni^IILn^III₂ series have been realized. As far as our knowledge goes, this Ni^II–Ln^III–Ln^III topology has not been reported in the literature to date. In-depth structural analysis of the ligand and the complexes has been carried out and this structural understanding will enable us to correlate the structure–property relationship in a better way. Magnetic studies indicated that the Dy^III analogue exhibits the slow relaxation of magnetization behavior under 800 Oe external dc field with energy barrier 2.94 K.