Thermally Triggered Solid‐State Single‐Crystal‐to‐Single‐Crystal Structural Transformation Accompanies Property Changes

The 1D complex [(CuL_0.5H₂O) ? H₂O]_n ( 1 ) (H₄L=2,2′‐bipyridine‐3,3′,6,6′‐tetracarboxylic acid) undergoes an irreversible thermally triggered single‐crystal‐to‐single‐crystal (SCSC) transformation to produce the 3D anhydrous complex [CuL_0.5]_n ( 2 ). This SCSC structural transformation was confirmed by single‐crystal X‐ray diffraction analysis, thermogravimetric (TG) analysis, powder X‐ray diffraction (PXRD) patterns, variable‐temperature powder X‐ray diffraction (VT–PXRD) patterns, and IR spectroscopy. Structural analyses reveal that in complex 2 , though the initial 1D chain is still retained as in complex 1 , accompanied with the Cu‐bound H₂O removed and new O(carboxyl)?Cu bond forming, the coordination geometries around the Cu^II ions vary from a distorted trigonal bipyramid to a distorted square pyramid. With the drastic structural transition, significant property changes are observed. Magnetic analyses show prominent changes from antiferromagnetism to weak ferromagnetism due to the new formed Cu1‐O‐C‐O‐Cu4 bridge. The catalytic results demonstrate that, even though both solid‐state materials present high catalytic activity for the synthesis of 2‐imidazolines derivatives and can be reused, the activation temperature of complex 1 is higher than that of complex 2 . In addition, a possible pathway for the SCSC structural transformations is proposed.