In the present communication we report a model that describes the valence tautomeric transformation in a crystal consisting of heterometallic [Cr-dhbq-Co] molecules. The model takes into account the states arising from two different configurations of the molecule, namely, Cr³⁺-dhsq³⁻-Co³⁺ and Cr³⁺-dhsq²⁻-Co²⁺, the Heisenberg exchange interaction between the dhsq³⁻ ligand and the Cr³⁺ ion as well as the cooperative electron-deformational and dipole-dipole interactions. The problem is solved in the mean field approximation. The main peculiarities of the valence tautomeric transformation are elucidated. It is demonstrated that the electron transfer ligand-Co is accompanied not only by the significant increase of the effective magnetic moment but also by the appreciable change in the microscopic polarization. The model provides quite a good description of the experimental data on the temperature dependence of the effective magnetic moment in the [(Cr(SS-cth))(Co(RR-cth))(μ-dhbq)](PF₆)₃ compound.