A model has been developed to describe the valence tautomeric transformation in a crystal containing as a structural element trinuclear complexes with electronic configurations Cr3+ dhsq3-low-spin Co3+ and Cr3+ dhbq2-high-spin Co2+ at low and high temperatures, respectively. The model takes into account the antiferromagnetic exchange coupling between the dhsq3-ligand with the itinerant electron and the Cr3+ - ion, the ferromagnetic exchange coupling Cr3+ high-spin Co2+ as well as the interaction of the Co-ion with the full symmetric breathing mode of the nearest crystal surrounding producing a strong localizing effect. In the model there are also accounted for the cooperative dipole-dipole and electron-deformational interactions. The parameters of the main interactions governing the observed phenomena are evaluated through DFT calculations. The interplay between the intracluster exchange coupling and the cooperative interactions has been demonstrated to lead to gradual and abrupt spin transitions as well as to those accompanied by a hysteresis loop. Within the framework of the suggested model a qualitative and quantitative explanation is given of the magnetic susceptibility of the [(Cr(SS-cth)(Co(RR-cth)( compound.