Recently the compound {[Co(tmphen)2]3[Fe(CN)6]2} has been found to exhibit a temperature-driven chargetransfer induced spin transition (CTIST) [1]. In order to understand the main factors governing this transition here we present a theoretical approach for the description of the CTIST in a model crystal consisting of dimeric Fe-Co clusters. The model takes into account : (i) the interaction of the Fe and Co-ions with the crystal field; (ii) the electron transfer processes; (iii) the exchange interaction in the pairs ls-Co(II)--ls-Fe(III), hs-Co(II)--ls-Fe(III), (iv) the cooperative electron-deformational interaction arising from the transition ls-Co(III)--hs-Co(II). In calculations of the magnetic characteristics and the temperature dependence of the Mossbauer spectra as a basis set we take the states of a molecule with localized electrons arising from its three configurations: I. ls Co(III) , lsFe(II) ; II. ls Co(II) , lsFe(III) ; III. hs Co(II) , lsFe(III). The states of configuration I belong to the total spin value S=0, the states of configurations II and III possess , respectively, the spin values 0,1 and 1,2. The model also accounts for the fact that the states of configurations I and II belonging to the total spin S=0 of the pair are connected by electron transfer. In order to treat the cooperative electron-deformational interaction the mean field approximation is applied. The energies of the levels and corresponding wave-functions obtained in this approximation have been used for the calculation of the temperature dependence of the effective magnetic moment (Fig.1) and Mössbauer spectra. It was demonstrated that the CTIST is most pronounced when the states arising from configuration III are the closest to the ground level arising from configuration I . The Mossbauer spectra are shown to reflect the redistribution of the electronic density within the cluster.figureFig.1 Temperature dependence of effective magnetic moment 1. t=300 cm-1 (transfer parameter )and #(II,I)= 300cm-1, #(III,I) = 600cm-1. 2. t=50 cm-1 and #(II,I)= 300cm-1,# (III,I) = 600cm-1 3. t=300 cm-1 and #(II,I)= 600cm-1, (III,I) = 300cm-1 4. t=50 cm-1, 2 # = 300cm-1(II,I)= 600cm-1, #(III,I) = 300cm-1, #(i,I), is the effective gap between the states of configurations i=II,III and I.