See-Saw Shaped Dy(III) Single-Molecule Magnets with High Anisotropy Barriers

Utilizing a terphenyl bisanilide ligand, two Dy(III) complexes [K(DME)_x][L^ArDy(X)₂] (L^Ar = {C₆H₄[(2,6-ⁱPrC₆H₃)NC₆H₄]₂}^2-), X = Cl (1) and X = I (2) were synthesized. The ligand imposes an unusual see-saw shaped molecular geometry leading to a coordinatively unsaturated complex with near-linear N-Dy-N (avg. 159.9° for1 and avg. 160.3^o for 2) bond angles. These complexes exhibit Single-Molecule Magnet (SMM) behavior with significant uniaxial magnetic anisotropy as a result of the transverse coordination of the bisanlide ligand which yields high energy barriers to magnetic spin reversal of U_eff = 1334 K/ 927cm^-1 (1) and 1299 K/ 903 cm^-1 (2) in zero field. Magneto-structural correlations are discussed with the goal of finding a link between halide ancillary ligands in the structurally analogous complexes and the through barrier relaxation dynamics observed in the ac magnetic susceptibility, despite the similar dc magnetic susceptibility for compounds 1 and 2. Ab initio calculations reveal that the dominant crystal field of the bisanilide ligand controls the orientation of the main magnetic axis which runs nearly parallel to the N-Dy-N bonds, and defines the height of the energy barrier. Thus, further validating the use of transverse ligands to enhance the SMM properties of Dy(III) ions.