Reversible Shuttle Action upon Dehydration and Rehydration Processes in Cationic Coordinatively-Bonded (4,4) Square-Grid Nets Threaded by Supramolecular Bonded Anions, {[Cu<sup>II</sup>(4,4′-bpy)<sub>2</sub>(H<sub>2</sub>O)][Cu<sup>II</sup>(2-pySO<sub>3</sub>)<sub>3</sub>](NO<sub>3</sub>)}·H<sub>2</sub>O

{[Cu<sup>II</sup>(4,4′-bpy)<sub>2</sub>(H<sub>2</sub>O)][Cu<sup>II</sup>(2-pySO<sub>3</sub>)<sub>3</sub>](NO<sub>3</sub>)}·H<sub>2</sub>O, obtained serendipitously by the reaction of the constituents in water, consists of parallel coordinatively bonded cationic (4,4) corrugated square-grids polymer of {[Cu<sup>II</sup>(4,4′-bpy)<sub>2</sub>(H<sub>2</sub>O)]<sup>2+</sup>}<sub><i>n</i></sub> threaded by π−π and H-bonded supramolecular chains of [Cu<sup>II</sup>(2-pySO<sub>3</sub>)<sub>3</sub>]<sup>−</sup> through the open squares. A single-crystal to single-crystal transformation takes place upon removal of the noncoordinated water by controlled heating. The resulting structure exhibits a rearrangement of the coordination of the copper atoms in the grids, where the Cu−H<sub>2</sub>O bond is elongated from 2.250(3) to 2.628(3) Å while the Cu-NO<sub>3</sub> is shortened from 3.122(3) to 2.796(1) Å. This process is reversible as demonstrated by the single crystal structure after rehydration with corresponding bond distances of 2.224(3) and 3.152(3) Å. Such a cooperative effect may be associated with the Jahn−Teller distortion of the copper(II) ion accompanying the shuttle action of the hydrogen-bonded water and nitrate moiety.