Modeling of the Charge-Transfer-Induced Spin Transition in the Tetranuclear Cyanide-Bridged [Co₂Fe₂] Complex

The course of the charge-transfer-induced spin transition demonstrated by the cyanide-bridged tetranuclear [Co₂Fe₂(bpy*)₄(CN)₆(tp*)₂](PF₆)₂·2CP·8BN complex has been followed by DFT calculations of the single-point energies for different total spin values of the complex in a wide temperature range. With the aid of these calculations, the picture of spin conversion, that the compound undergoes, has been restored. It has been demonstrated that at 100 K the two crystallographically unique tetranuclear Fe₂Co₂ subunits A and B present in the structure contain diamagnetic low-spin Fe^II and low-spin Co^III ions. From the three subunits A, A', and B detected crystallographically in the compound at 200 K, only the A ones contain paramagnetic low-spin Fe^III and high-spin Co^II ions, while at 260 K, a half of all clusters contained in the crystal are in this state. From the DFT calculations, it also follows that at 320 K in the crystal only paramagnetic units are present. The results obtained are in accordance with the experimental data on the magnetic susceptibility. A possibility to predict new materials exhibiting spin transitions on the basis of DFT calculations of single-point energies as functions of temperature is discussed.