Influence of Tuned Linker Functionality on Modulation of Magnetic Properties and Relaxation Dynamics in a Family of Six Isotypic Ln₂ (Ln = Dy and Gd) Complexes

A coordination complex family comprising of six new dinuclear symmetric lanthanide complexes, namely, [Ln₂(L_x)₂(L′)₂(CH₃OH)₂]·yG (H₂L_x: three related yet distinct Schiff-base linkers; x = 1-3, according to the nomenclature of the Schiff-base linker employed herein. HL′: 2,6-dimethoxyphenol. yG refers to crystallographically assigned guest solvent species in the respective complexes; y = number of solvent molecules; Ln^III = Dy/Gd) were isolated employing a mixed-ligand strategy stemming out of a strategic variation of the functionalities introduced among the constituent Schiff-base linkers. The purposeful introduction of three diverse auxiliary groups with delicate differences in their electrostatic natures affects the local anisotropy and magnetic coupling of Ln^III ion-environment in the ensuing Ln₂ dinuclear complexes, consequentially resulting into distinctly dynamical magnetic behaviors among the investigated new-fangled family of isotypic Ln₂ complexes. Among the entire family, subtle alterations in the chemical moieties render two of the Dy₂ analogues to behave as single molecule magnets, while the other Dy₂ congener merely exhibits slow relaxation of the magnetization. The current observation marks one of the rare paradigms, wherein magnetic behavior modulation was achieved by virtue of the omnipresent influence of subtly tuned linker functionalities among the constituent motifs of the lanthanide nanomagnets. To rationalize the observed difference in the magnetic coupling, density functional theory and ab initio calculations (CASSCF/RASSI-SO/POLY-ANISO) were performed on all six complexes. Subtle difference in the bond angles leads to difference in the J values observed for Gd₂ complexes, while difference in the tunnel splitting associated with the structural alterations lead to variation in the magnetization blockade in the Dy₂ complexes.