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

Two dichloride‐bridged dinuclear dysprosium(III) complexes based on salen ligands, namely, [Dy(L 1 )(μ‐Cl)(thf)] 2 ( 1 ; H 2 L 1 = N,N ′‐bis(3,5‐di‐ tert ‐butylsalicylidene)phenylenediamine) and [Dy 2 (L 2 ) 2 (μ‐Cl) 2 (thf) 2 ] 2 ( 2 ; H 2 L 2 = N,N ′‐bis(3,5‐di‐ tert ‐butylsalicylidene)ethylenediamine) are reported. These two complexes have two short Dy−O (PhO) bonds that exhibit 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 [Dy 2 (L 3 ) 2 (μ‐Cl) 2 (thf) 2 ] ( 3 ; H 2 L 3 = N ‐(2‐pyridylmethyl)‐ N N ‐bis(2′‐hydroxy‐3′,5′‐di‐ tert ‐butylbenzyl)amine). The only substantial difference is the relative angle of the two O (PhO) −Dy−O (PhO) vectors, which is collinear in 2 owing to inversion symmetry and ∼68° in 3 due to a molecular C 2 axis. It is shown 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 .