Single Crystal to Single Crystal Transformation of Cu II Complexes Induced by Dehydrating and Hydrating of Ligands with Chroma Rewritable Behaviors.

In this work, the single crystal to single crystal (SCSC) transformations in three mononuclear copper complexes [Cu L ² ₂ ]Cl ₂ ·2H ₂ O ( 1 ), [Cu L ¹ ₂ Cl ₂ ] ( 2 ), and [Cu L ² ₂ ]Cl ₂ ·4H ₂ O ( 3 ) ( L ¹ = di-2-pyridyl ketone, L ² = di(pyridin-2-yl)methanediol) are realized by the irreversible dehydration and hydration reaction of L ¹ and L ² . Dark purple crystal 1 is obtained by self-assembly of L ¹ and CuCl ₂ ·2H ₂ O in solvothermal reactions, in which the carbonyl group of L ¹ undergoes a hydration addition reaction to form L ² . On heating, 1 transforms to 2 by dehydrating water accompanied by the change of the color and coordination octahedron of Cu ^II ions. In a saturated water vapor environment, 2 can absorb six water molecules and transform to 3 with the same color and coordination environment with 1 but different lattice water. The SCSC process from 2 to 3 is reversible: 3 can transform back to 2 on heating like that of 1 . Chroma rewritable behaviors in the structural transformation of the complexes make them visually identifiable temperature or water probes.