Here we repo1i the synthesis, experimental and theoretical study of a family of linear trimeric [NE4] {[Mn(L)h[M(CN)6]} (M = Fe, Ru, Os) compounds that demonstrate slow relaxation of magnetization at low temperatures. The model for the explanation of de magnetic behavior of all three complexes (the magnetic susceptibility as a function of temperature and magnetization as a function of the applied mmagnetic m field includes the spin-orbital interaction acting within the ground T1 multiplet of the Fe , Ru or Os ion, the axial c1ystal field that splits this multiplet into an orbital singlet and orbital doublet, the zero-field splitting for the Mnm ions, the isotropic exchange interaction in the M-Mn pairs as well as the intercluster interaction taken within the mean field approximation. The proposed model provides a good agreement between the observed and calculated de magnetic behavior of all examined compounds. In the Fig. I as an example the experimental data and the results of modeling for the Mn-Fe-Mn trimer are presented. For each cluster the pattern of low-lying energy levels has been rebuilt. The possible one­phonon transitions which depopulate the ground state of each cluster and are responsible for the magnetic relaxation were detennined. The calculated heights of the baiTiers for magnetization reversal 16.1, 16.8 and 22.8 cm-1 for MnFeMn, MnRuMn and MnOsMn complexes, respectively, ai·e close to the experimentally observed ones: 13.3, 14.8 and 17.7 cm-1.