A theoretical model has been developed to explain at the electronic level the charge transfer induced spin transition (CTIST) ls-FeII−ls-CoIII → ls-FeIII−hs-CoII (ls−low-spin, hs−high-spin) 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 also includes the electron transfer in the Fe-Co pairs and intracluster magnetic exchange. The conditions favorable for charge transfer induced spin transitions have been discussed. It was shown that depending on the ratio between the transfer parameter and energy gaps between the ground configuration presented by diamagnetic ls-CoIII and ls-FeII ions (configuration I) and excited configurations II and III containing, respectively, paramagnetic ions ls-FeIII and ls-CoII or ls-FeIII and hs-CoII the charge transfer induced spin transition can be a gradual or an abrupt one. The cooperative electron-deformational interaction appreciably affects the spin transformation in the case when the parameters of this interaction are of the same order of magnitude with the parameter t characterizing the electron transfer from the iron to the cobalt ion. The intracluster exchange interaction in the cyanide-bridged ls-FeIII−ls-CoII and ls-FeIII−hs-CoII pairs does not influence noticeably the spin transition since it is of the order of several wavenumbers. The energy diagram that gives the possibility to explain qualitatively the observed Mössbauer spectra transformations [1] corresponds to the case of the transfer parameter small as compared with the energy gaps between the localized states of configurations I, II, III under the condition that the states of configuration III are lower in energy than those of configuration II. It should be stressed that in spite of several restricting assumptions made in the consideration carried out, the suggested model reflects the main qualitative features of the observed phenomenon.