Synthesis and size control of iron(II) hexacyanochromate(III) nanoparticles and the effect of particle size on linkage isomerism

The controlled synthesis of monodisperse nanoparticles of the cubic Prussian blue analogue iron(II) hexacyanochromate(III) is reported along with a kinetic study, using cyanide stretching frequencies, showing the variations of the activation energy (E_a) of the linkage isomerism as a function of the particle size. Highly reproducible, cubic-shaped iron(II) hexacyanochromate(III) nanocrystals, with sizes ranging from 2 to 50 nm, are synthesized using a microemulsion technique, whereas a bulk synthesis yields nonuniform less monodisperse particles with sizes greater than 100 nm. Monitoring the cyanide stretching frequency with FTIR spectroscopy shows that the rate of isomerization is faster for smaller particles. Moreover, a kinetic analysis at different temperatures (255 K ≤ T ≤ 321 K) gives insight into the evolution of E_a with the particle size. Finally, time-dependent powder X-ray diffraction and net magnetization confirm the FTIR observations. The data are interpreted within the concept of a simple two-component model with different activation energies for structures near the surface of the solid and within the bulk.