The material under study belongs to the Prussian blue analogues family, which are coordination compounds with a porous framework appropriate for the storage of small molecules, among them hydrogen. The porous framework results from systematic vacancies for the octahedral building block, [M(CN)6], in a 3D structure. Mössbauer spectroscopy is a powerful tool to obtain structural information on the local environment for the iron nucleus in these materials. Mössbauer spectra of iron (2+) hexacyanometallates (III) show two slightly asymmetric quadrupole splitting doublets. These two doublets correspond to two non-equivalent structural sites for the iron atom in the framework related with a non-random vacancy distribution. The observed asymmetry was ascribed to a vibrational anisotropy for these iron sites. The asymmetry decreases on the sample cooling and for 7 K it practically disappears. The iron atom is found at the cavities surface with a mixed coordination sphere, Fe(NC)6-r(H2O)r. Such anisotropic coordination environment could explain the presence of certain vibrational anisotropy detected as asymmetric quadrupole splitting doublets. © by Oldenbourg Wissenschaftsverlag, München.
Reguera, E., Yee-Madeira, H., Demeshko, S., Eckold, G., & Jimenez-Gallegos, J. (2009). Nature of the observed asymmetry in mossbauer spectra of iron (2+) hexacyanometallates (III). Zeitschrift fur Physikalische Chemie, 701-711. https://doi.org/10.1524/zpch.2009.5455