X‐Ray Triggered Coordination‐Bond Breakage in Dysprosium‐Organic Framework and its Impact on Magnetic Properties

Photosensitive lanthanide‐based single‐molecule magnets (Ln−SMM) are very attractive for their potential applications in information storage, switching, and sensors. However, the light‐driven structural transformation in Ln−SMMs hardly changes the coordination number of the lanthanide ion. Herein, for the first time it is reported that X‐ray ( λ =0.71073 Å) irradiation can break the coordination bond of Dy−OH 2 in the three‐dimensional (3D) metal‐organic framework Dy 2 (amp 2 H 2 ) 3 (H 2 O) 6 ⋅ 4H 2 O ( MDAF‐5 ), in which the {Dy 2 (OPO) 2 } dimers are cross‐linked by dianthracene‐phosphonate ligands. The structural transformation proceeds in a single‐crystal‐to‐single‐crystal (SC‐SC) fashion, forming the new phase Dy 2 (amp 2 H 2 ) 3 (H 2 O) 4 ⋅ 4H 2 O ( MDAF‐5‐X ). The phase transition is accompanied by a significant change in magnetic properties due to the alteration in coordination geometry of the Dy III ion from a distorted pentagonal bipyramid in MDAF‐5 to a distorted octahedron in MDAF‐5‐X .