Vacancy-Induced Deformation in a CoFe Prussian Blue Analogue - A Theoretical Investigation

The impact of the number and positions of Rb ions in the RbCo[Fe(CN)(6)] Prussian blue analogue is analyzed by means of complete active space self-consistent field (CASSCF) and subsequent second-order perturbation theory (CASPT(2)) calculations performed upon embedded cluster models. It is shown that the geometries and corresponding electronic structures of the monomeric [CoIII(NC)(5)(OH2)](2) and [CoII(NC)(5)(OH2)](3) units are differently affected when the apical cyanide ligand is substituted by a water molecule. The Co-III ion moves away from the equatorial plane by ca. 0.15 angstrom, whereas the Co-II is almost not sensitive to the environmental change. Furthermore, we find that this phenomenon is rather independent of the positions and numbers of the nearest-neighbour alkali ions. The Co ion displacement directly controls the overlap between the bridging cyanide and metal ion orbitals, a scenario which might be favorable to trigger electron transfer in the photomagnetic dimeric CoFe units of the CoFe Prussian blue analogues.