Magnetic Switching in a Dynamic Cobalt(II)-Carboxylate Framework via a Concerted Crystal-to-Crystal Chemical Transformation

Dynamic modulation of magnetic properties by means of single-crystal-to-single-crystal (SC-SC) chemical transformations constitutes a pervasive challenge. In this study, we report the dynamic switching of structures and magnetic properties in a cobalt-carboxylate framework through a synergistic crystal-to-crystal chemical transformation. Variable-temperature single-crystal X-ray diffraction reveals the hexanuclear cobalt(II) framework exhibited a structural phase transition from [Co6(ip)5(H2O)2(μ3–OH)2(DMF)2]·DMF (Co6·DMF, ip = isophthalic acid) to [Co6(ip)5(μ3–OH)2(DMF)3] (Co6) involving the removal of two coordinated water molecules and in situ coordination of guest DMF. The concerted substitution reaction induced a significant modification of the coordination geometries of the Co6 nodes (octahedron and tetrahedron in Co6·DMF; octahedron, square pyramid, and tetrahedron in Co6). Though the nodes in the framework are distinct, the sxb topology remains unchanged. Static magnetic studies reveal that this structural transformation induces a magnetic change from strong antiferromagnetic (Weiss constants θ = −55.77 K) to weak ferromagnetic (θ = 1.76 K) interactions. Dynamic magnetic studies indicate a turn-on effect of the slow relaxation of magnetization from Co6·DMF to Co6 at low temperature. Isothermal magnetization measurements also indicate a paramagnet- to a magnet-type switching from Co6·DMF to Co6. Detailed structural analysis reveals that this magnetic property switching is caused by the structural transformation induced by the concerted substitution reaction of coordinated water with guest DMF. These findings not only demonstrate the first sxb network showing magnetic switching via SC-SC chemical transformation but also introduce a concerted substitution reaction strategy for designing switchable magnetic materials.