Influence of Guest Exchange on the Magnetization Dynamics of Dilanthanide Single‐Molecule‐Magnet Nodes within a Metal–Organic Framework

Multitopic organic linkers can provide a means to organize metal cluster nodes in a regular three‐dimensional array. Herein, we show that isonicotinic acid N ‐oxide (HINO) serves as the linker in the formation of a metal–organic framework featuring Dy 2 single‐molecule magnets as nodes. Importantly, guest solvent exchange induces a reversible single‐crystal to single‐crystal transformation between the phases Dy 2 (INO) 4 (NO 3 ) 2 ⋅2 solvent (solvent=DMF (Dy 2 ‐DMF), CH 3 CN (Dy 2 ‐CH 3 CN)), thereby switching the effective magnetic relaxation barrier (determined by ac magnetic susceptibility measurements) between a negligible value for Dy 2 ‐DMF and 76 cm −1 for Dy 2 ‐CH 3 CN. Ab initio calculations indicate that this difference arises not from a significant change in the intrinsic relaxation barrier of the Dy 2 nodes, but rather from a slowing of the relaxation rate of incoherent quantum tunneling of the magnetization by two orders of magnitude.