Experimental and theoretical exploration of magnetic exchange interactions and single-molecule magnetic behaviour of bis(η1:η2:μ2-carboxylate)Gd III2/Dy III2 systems

Abstract

The present report deals with the syntheses, crystal structures, dc/ac magnetic properties and DFT/ab initio CASSCF calculations of two isomorphous bis(η¹:η²:μ₂-acetate)Gd^III₂/Dy^III₂ compounds of the formula [Ln^III₂L₂(acetate)₄(MeOH)₂] (1, Ln = Gd; 2, Ln = Dy), where HL is (E)-N′-(3-ethoxysalicylidene)acetohydrazide. The two lanthanide(III) centres in each compound are symmetry-related owing to the presence of an inversion centre. Both compounds exhibit intramolecular ferromagnetic exchange interactions. The Dy^III₂ analogue is a single-molecule magnet (SMM) with U_eff = 52.8 cm⁻¹ and τ₀ = 1.52 × 10⁻⁶ s. DFT calculations for 1 and ab initio calculations for 2 also reveal ferromagnetic interactions. Ab initio calculations of the SMM behaviour of 2 and two other reported and structurally related compounds reveal the importance of the weak exchange interaction present between the two Dy^III ions, and a relaxation mechanism has been developed to take into account the magnetic exchange interaction and to rationalize the observed difference in the U_eff values.