Facile preparation of Prussian blue analogue Co3[Co(CN)6]2 with fine-tuning color transition temperature as thermochromic material

For thermochromic materials, a fine-tuning thermochromic property is always pursued to in order to realize their full potential. However, to date, realizing the fine-tuning still remains a great challenge and is seldom reported. In the present work, the Prussian blue analogue, Co-3[Co(CN)(6)](2), with fine-tuning color transition temperature is synthesized through a facile wet-chemical method. By simply adjusting the amount of sodium citrate in the system, part of the ligand water molecules coordinated to lattice Co(II) can be substituted by citrate, which is confirmed by DFT calculations and experimental results, resulting in a color transition versus temperature as a response to a coordination environmental change of the Co(II). Finally, a fine-tuning color transition temperature from 40 to 80 degrees C is realized with the color changing from pink to blue upon heating. In addition to the tunable color transition temperature, a high color transition speed and long term stability were also achieved due to the porous and stable lattice structure of Co-3[Co(CN)(6)](2). To the best of our knowledge, this is the first report of a metal-organic framework ( MOF) with a fine-tuning reversible thermochromic property, and the present controlled strategy might be expanded to the preparation of other similar materials.