Reversible Double Nucleophilic Substitution Reaction inside Single-Crystal MOF Tuned Remarkable Magnetic Behavior.

Chemical reactions inside single crystals are highly selective but quite challenging. We present herein an octahedral cobalt-oxygen chain-based 3D coordination network with sqc3868 topology, which underwent a reversible double nucleophilic substitution inside a single crystal involving encapsulated DMF molecules and was converted into a topologically highly related frl network, accompanied by magnetic tuning from antiferromagnetism to ferromagnetism. Combined UV-vis, XPS, EPR, and XANES showed most of the Co centers keep a divalent state with less remarkable electronic structure change during the substitution reaction, indicating magnetic tunability mainly comes from a minor change of local geometry of cobalt atoms with large anisotropy.