The effect of the disposition of coordinated oxygen atoms on the magnitude of the energy barrier for magnetization reversal in a family of linear trinuclear Zn- Dy- Zn complexes with a square- antiprism DyO8 coordination sphere

A series of trimetallic Zn-Dy-Zn complexes of the general formula [ZnX(mu-L)Dy(mu-L)XZn]Y center dot nS, where H2L is the compartmental ligand N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromobenzyl) ethylenediamine, X is the coligand (X = Cl, Br, I and N-3), Y is the counteranion and S are the crystallization solvent molecules have been synthesized and magnetically characterized. In all these complexes, the Dy(III) ions exhibit DyO8 coordination environments with a slightly distorted square-antiprism D-4d symmetry. Due to the disposition of the oxygen atoms around the Dy(III) ions, large easy-axis anisotropy is expected, which is responsible for the high thermal energy barriers for the reversal of the magnetization observed at zero field (in the 144-170 K range for all complexes). A preliminary correlation between the disposition of the oxygen atoms of the ligand (phenoxo and aldehyde) in the DyO8 coordination sphere and the value of U-eff has been established.