Reversible On–Off Switching of a Single-Molecule Magnet via a Crystal-to-Crystal Chemical Transformation

Dynamic
molecular crystals are of high interest
due to their potential applications. Herein we report the reversible
on–off switching of single-molecule magnet (SMM) behavior in
a [Mo­(CN)7]4– based molecular compound.
Upon dehydration and rehydration, the trinuclear Mn2Mo
molecule [Mn­(L)­(H2O)]2[Mo­(CN)7]·2H2O (1) undergoes reversible crystal-to-crystal
transformation to a hexanuclear Mn4Mo2 compound
[Mn­(L)­(H2O)]2[Mn­(L)]2[Mo­(CN)7]2 (2). This structural transformation
involves the breaking and reforming of coordination bonds which leads
to significant changes in the color and magnetic properties. Compound 1 is an SMM with an energy barrier of 44.9 cm–1, whereas 2 behaves as a simple paramagnet despite its
higher ground state spin value. The distortion of the pentagonal bipyramidal
geometry of [Mo­(CN)7]4– in 2 disrupts the anisotropic exchange interactions that lead to SMM
behavior in 1.