Dehydration-Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged Dy~ⅢCo~Ⅲ Framework

摘要

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) cyanidobridged coordination polymer, {[Dy-III(H2O)(2)][Co-III(CN)(6)]}center dot 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(mu-NC)(6)(H2O)(2)](3-) square antiprism geometry, while the dehydrated form contains six-coordinated [Dy-III(mu-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.