Dinuclear Dy2 Single‐Molecule Magnets: Functional Modulation on the Bridging Ligand and Different Relaxation Performances within the Single‐Crystal to Single‐Crystal System

Abstract Crystal structures, single‐molecule magnetic behavior, and ab initio calculations of four new phenoxo‐bridged dinuclear dysprosium complexes and their gadolinium(III) analogues are explored. Complexes [Dy 2 (DMOMP) 2 (DBM) 4 ] 2 ⋅ CHCl 3 ( 1 ; DMOMP=1‐methyl‐3,5‐dimethoxy‐4‐hydroxybenzene, DBM=1,3‐diphenylpropane‐1,3‐dione); [Dy 2 (DMOAP) 2 (DBM) 4 ] 2 ⋅ CHCl 3 ( 2 ; DMOAP=syringaldehyde); Dy 2 (DMOEP) 2 (DBM) 4 ( 3 ; DMOEP=methyl syringate); and solvent‐free Dy 2 (DMOMP) 2 (DBM) 4 ( 4 ), which is obtained by the transformation of single crystal into single crystal from 1 , have nearly identical core structures and only differ in the substituents at the para position of the phenol moieties of the bridging ligand. In this system, the electronic effects are efficiently implemented to significantly modify the ligand field strength and exchange coupling by modulating the substituents on the phenol backbone. The effective energy barrier ( U eff ) of magnetization reversal is improved significantly to fivefold magnitude, at most, and the hysteresis temperature up to 3.5 K by deliberately using the electron‐withdrawing substituent to replace the electron‐donating one. The origin of the two relaxation processes in 1 is mostly attributed to the existence of two molecules in one unit, which is illuminated by means of the transformation of single crystal into single crystal.