Growth of Prussian Blue Microcubes under a Hydrothermal Condition: Possible Nonclassical Crystallization by a Mesoscale Self-Assembly

A classical crystallization process starts from stable nuclei followed by a simple enlargement of the nuclei by unit-cell replication. In recent years, the universality of such classical crystallization has been questioned upon investigations of biomineralization processes, and there are few examples showing that crystal growth may not follow such a classical crystallization process. In this paper, a typical coordination polymer, Prussian blue microcrystals, has been synthesized under hydrothermal conditions. By carefully analyzing the intermediates during the crystal growth process, we found that the growth of Prussian blue under the given growth conditions may follow a nonclassical crystal growth process in which a mesoscale self-assembly of nanocrystallites is included during crystal growth. Such a mesoscale self-assembly process could be a common phenomenon for growth of some crystals with extremely low solubility.