Determinative Effect of Axial Linearity on Single‐Molecule Magnet Performance in Dinuclear Dysprosium Complexes

We report two dichloride-bridged dinuclear dysprosium(III) complexes based on salen ligands, namely, [Dy(L1)(μ-Cl)(thf)]2 (1; H2L1 = N,Nʹ-bis(3,5-di-tert-butylsalicylidene)phenylenediamine) and [Dy2(L2)2(μ-Cl)2(thf)2]2 (2; H2L2 = N,Nʹ-bis(3,5-di-tert-butylsalicylidene)ethylenediamine). These two complexes have two short Dy−O(PhO) bonds that have angles of ~90° for 1 and ~143° for 2, leading to clear slow relaxation of the magnetization for 2 and not for 1. Compound 2 has a near-identical core to the recently reported compound [Dy2(L3)2(μ-Cl)2(thf)2] (3; H2L3 = N-(2-pyridylmethyl)-N,N-bis(2ʹ-hydroxy-3ʹ,5ʹ-di-tert-butylbenzyl)amine), the only substantial difference being the relative angle of the two O(PhO)−Dy−O(PhO) vectors, which are collinear in 2 owing to inversion symmetry and make an angle of ~68° in 3 owing to a molecular C2 axis. We show that this subtle structural difference leads to large differences in the dipolar ground states, giving rise to open magnetic hysteresis for 3 and not for 2.