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 FeII and low-spin CoIII 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.

Automated summary

The charge-transfer-induced spin transition of the cyanide-bridged tetranuclear complex [Co2Fe2(bpy*)(4)(CN)(6)(tp*)(2)](PF6)(2)-2CP-8BN has been studied using DFT calculations of single-point energies at various temperatures. The results reveal the spin conversion process of the compound and show that different spin states are present at different temperatures. The findings are consistent with experimental data on magnetic susceptibility, and the potential for predicting spin transitions in new materials based on DFT calculations is discussed.