Cyclic OFF/Part/ON switching of single-molecule magnet behaviours via multistep single-crystal-to-single-crystal transformation between discrete Fe(ii)-Dy(iii) complexes.

Upon dehydration, a dinuclear Fe(ii)-Dy(iii) cluster {FeDy(H2O)2} undergoes two-step single-crystal-to-single-crystal (SCSC) transformation, giving another dinuclear cluster {FeDy(H2O)} and finally a tetranuclear cluster {Fe2Dy2}. Further, both the single crystals of {FeDy(H2O)} and {Fe2Dy2} can return to {FeDy(H2O)2} by rehydration. This multistep SCSC transformation leads to notable OFF/Part/ON switching of single-molecule magnet behaviour.