The Mutation in the Single-Crystal Structural Transformation Process, Induced by the Combined Stimuli of Temperature and Solvent.

A 2D coordination polymer containing a free ligand (Lf ), fixed by hydrogen bonds, transformed into a 3D metal-organic framework (MOF) in a single-crystal to single-crystal fashion. This transformation occurs through the combined stimuli of temperature and solvent. From 50 to 90 °C, a series of changes take place in a gradual form: the Lf is slowly moved to the cobalt center, which is accompanied by a contraction of unit cell and hydrogen bond. When the temperature rises to 95 °C, the hydrogen bond is destroyed, and Lf is suddenly combined with the cobalt ion to form an intricate 3D structure. This mutation process is irreversible and cannot occur just with the stimulus of either temperature or solvent. Notably, even under the combined stimuli, this mutation phenomena is difficult to reproduce when the solvent species and proportions change. DFT calculations were used to try to explain the nature of the phenomenon.