Biomimetic Transformation by a Crystal of a Chiral Mn^II–Cr^III Ferrimagnetic Prussian Blue Analogue

We present a case of a concerted sequence of several characteristic biological reactions such as electron transfer, mixed valency, proton or ion motion, and dehydration–rehydration occurring in a single crystal and its associated phase transformations. It provided a unique opportunity to look for accurate pictures of sequence mimicking biological function using crystallography. Here, we report the observation of a reversible musclelike action associated with proton motion between ammonium and coordinated and uncoordinated water molecules in unison in which the whole X-ray diffraction study (including eight structure determinations as a function of temperature and cycling through two phase transformations) was performed in situ on a single crystal of the chiral molecular magnet [Mn II ( R - pn H)(H 2 O)][Cr III (CN) 6 ]·H 2 O [ R - pn = ( R )-1,2-propanediamine]. In addition, the reversible structural change in dimensionality from two- to three-dimensional is observed with an increase in the ferrimagnetic Curie temperature from 38 to 73 K upon dehydration.