A flexible coordination polymer crystal providing reversible structural and magnetic conversions

Structural flexibility is a remarkable characteristic of coordination polymers and significant for the attainment of environmental responsivity. We have prepared a 2D cyanide-bridged Mn^IICr^III coordination polymer, [Mn(NNdmenH)(H₂O)][Cr(CN)₆]·H₂O (1; NNdmen = N,N-dimethylethylenediamine), with sophisticatedly arranged removable water coligands. The compound clearly showed a reversible single-crystal-to-single-crystal transformation between the 2D sheet and a 3D pillared-sheet framework of dehydrated [Mn(NNdmenH)][Cr(CN)₆] (1a). The structural change was reversible and accompanied with generation/cleavage of CN-Mn bonds between 2D sheets by dehydration/hydration. Compounds 1 and 1a also exhibited a ferrimagnetic ordering at 35.2 and 60.4 K, respectively, and the magnetic characteristics were reversibly converted by guest adsorption/ desorption. In addition, the dehydrated 1a demonstrated a size-selective solvent adsorption linking chemi- and physisorption processes and shrinkage/expansion of its framework. The flexible magnetic framework incorporating removable coligands delivered multifunctions with chemical response.