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)(mu-Cl)(thf)](2) (1; H2L1= N,N'-bis(3,5-di-tert-butylsalicylidene)phenylene-diamine) and [Dy-2(L-2)(2)(mu-Cl)(2)(thf)(2)](2) (2; H2L2 = 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 similar to 90 degrees for 1 and similar to 143 degrees 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)(mu-Cl)(2)(thf)(2)] (3; H2L3= 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 similar to 68 degrees 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.