A theoretical model has been developed to explain at the electronic level the charge-transfer-induced spin transition (CTIST) in crystals based on cyano-bridged binuclear Fe-Co clusters. The CTIST is considered as a cooperative phenomenon (phase transformation) driven by the long-range electron-deformational interaction via the acoustic phonons field that is taken into account within the mean field approach. The model for CTIST includes also the metal-metal electron transfer and intracluster magnetic exchange. The conditions that favor the CTIST are discussed. The qualitative explanation of the experimental data is given.

A microscopic approach to the problem of cooperative spin crossover in the [MnL2]NO3 crystal, which contains Mn(III) ions as structural units, is elaborated on, and the main mechanisms governing this effect are revealed. The proposed model also takes into account the splitting of the low-spin 3T1 (t(2)(4)) and high-spin 5E (t(2)(3)e) terms by the low-symmetry crystal field. The low-spin → high-spin transition has been considered as a cooperative phenomenon driven by interaction of the electronic shells of the Mn(III) ions with the all-around full-symmetric deformation that is extended over the crystal lattice via the acoustic phonon field. The model well explains the observed thermal dependencies of the magnetic susceptibility and the effective magnetic moment.

The manifestations of an external direct current (dc) electric field on the magnetic and polarizability characteristics of trimeric Cu II -Cu II -Cu III mixed-valence clusters were examined. The temperature and field dependence of the magnitude of the mean dipole moment as well as of its components were calculated, and the anisotropy of the cluster polarizability was predicted. The low-temperature limit of the cluster magnetic moment is determined by the competition between the

A crystal containing the heterometallic Cr-ligand-Co cluster with an unpaired electron on the ligand as a structural unit is examined. The developed model which describes the magnetic and polarizability characteristics...

We present a new microscopic approach for the description of the effects of an external direct current (dc) electric field on the magnetic, polarizability, and spectroscopic characteristics of molecular crystals containing cyanide‐bridged Fe–Co clusters as structural units. In addition to the interaction with the electric field, the model allows for metal–metal electron transfer, intracluster magnetic exchange, and long‐range electron‐deformational interactions, which are taken into account within the mean‐field approach. The external electric field gives a unique possibility to manipulate the polarizability, magnetic, and spectroscopic characteristics of cyanide‐bridged Fe–Co clusters.

A possibility to manipulate the magnetic and polarizability characteristics of systems containing mobile electrons by means of external fields opens new perspectives for molecular electronics. From this point of view mixed valence clusters d 1 −d 3 with two-electron transfer are a challenging subject, since under the action of the constant external electric field, it is possible not only to manipulate with the spin of the ground state of the cluster and, consequently, with its magnetic properties but also to produce a pronounced significant polarizability due to the suppression of the twoelectron tunneling by this field. The intracluster Heisenberg exchange interaction, the difference in Coulomb interaction for possible cluster configurations, and the coupling with an external electric field are taken into consideration in the model, which predicts spin transitions that are induced by this field and accompanied by appreciable changes in the magnetic properties and polarizability.

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