Dehydration–Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged DyIIICoIII Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration–hydration process within a bimetal coordination framework results in the switching of emissive Dy III single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[Dy III (H 2 O) 2 ][Co III (CN) 6 ]}·2.2H 2 O ( 1 ), and its dehydrated form of {Dy III [Co III (CN) 6 ]} ( 2 ), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic Dy III centers alternately arranged with diamagnetic hexacyanidocobaltates(III). The hydrated phase contains eight-coordinated [Dy III (μ-NC) 6 (H 2 O) 2 ] 3– complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [Dy III (μ-NC) 6 ] 3– moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of Dy III single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for Dy III sites in 1 . The D 4d -to- D 3h symmetry change of Dy III complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f–f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic Dy III complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of Dy III complexes embedded in a 3-D cyanido-bridged framework.