Tuning the Magnetic Interactions and Relaxation Dynamics of Dy 2 Single‐Molecule Magnets

Efficient modulation of single‐molecule magnet (SMM) behavior was realized by deliberate structural modification of the Dy 2 cores of [Dy 2 ( a ′ povh ) 2 (OAc) 2 (DMF) 2 ] ( 1 ) and [Zn 2 Dy 2 ( a′povh ) 2 (OAc) 6 ] ⋅ 4 H 2 O ( 2 ; H 2 a ′ povh = N ′‐[amino(pyrimidin‐2‐yl)methylene]‐ o ‐vanilloyl hydrazine). Compound 1 having fourfold linkage between the two dysprosium ions shows high‐performance SMM behavior with a thermal energy barrier of 322.1 K, whereas only slow relaxation is observed for compound 2 with only twofold connection between the dysprosium ions. This remarkable discrepancy is mainly because of strong axiality in 1 due to one pronounced covalent bond, as revealed by experimental and theoretical investigations. The significant antiferromagnetic interaction derived from bis(μ 2 ‐O) and two acetate bridging groups was found to be crucial in leading to a nonmagnetic ground state in 1 , by suppressing zero‐field quantum tunneling of magnetization.