• Ab initio calculations;
  • Photo­magnetism;
  • Spin crossover;
  • Cobalt;
  • Iron;
  • Prussian blue


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 (CASPT2) 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 CoIII ion moves away from the equatorial plane by ca. 0.15 Å, whereas the CoII 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.