Semiquantitative studies on the correlations between the electrostatic potential of a single DyIII ion and its energy barrier in the containing-DyIII single molecule magnets

Abstract

Although the design of containing-Dy^III single molecule magnets (SMMs) based on electrostatic potential has been employed for several years, rational studies on the correlations between the electrostatic potential of a single Dy^III ion and its energy barriers have not been reported previously. In this work, a novel “Y”-shaped Mn^III₅Dy^III₃ complex, [Mn^III₅Dy^III₃(NO₃)(OCH₃)(L)₄(L′)₂(tea)(teaH)₄]OH·3CH₃OH·2H₂O (1, H₂L = 2-methoxy-6-[(Z)-(1H-1,2,4-triazol-3-ylimino)methyl]phenol, H₃tea = triethanolamine and HL′ = 2-hydroxy-3-methoxybenzaldehyde), was obtained through the reaction of the H₂L ligand, teaH₃, Dy(NO₃)₃·6H₂O and MnCl₂·4H₂O in CH₃OH and DMF. Structural analysis revealed that the coordination geometry of Dy1 in 1 is muffin-like (MFF-9, C_s), while the geometries of Dy2 and Dy3 fall among spherical capped square antiprism-like (CSAPR-9, C_4v), spherical tricapped trigonal prism-like (TCTPR-9, D_3h) and muffin-like (MFF-9, C_s). Magnetic studies indicated that 1 exhibits slow magnetic relaxation behavior under zero dc field. More importantly, for the first time, we proposed the two parameters R_eq and R_ax to describe the relationship. The two parameters were employed for three Dy^III ions in 1, one Zn₂Dy complex and one mononuclear Dy complex reported by others. Results indicate that the calculated energy barrier (U_cal) continuously increases with decreasing R_ax absolute values. However, the higher the R_ax absolute values, the lower the U_cal values. This indicates that when the electrostatic potentials from two sides of the equatorial plane of Dy^III are completely equivalent to each other, U_cal is the highest. Moreover, POLY_ANISO and DFT calculations for 1 indicated that except for J₄ showing ferromagnetic coupling, all magnetic couplings are antiferromagnetic, which were interpreted from magneto-structural correlation.