A series of new heterotrinuclear transition-metal complexes [(Fe2MO)-M-I-O-I(OOCC2H5)(6)L-3] (M = Co, Ni, Mn; L = C5H5N, H2O) were synthesized and characterized. Their structures and dynamics in different solutions and temperatures were investigated by NMR and UV. Assignments of the H-1 NMR spectra were made on the basis of relative intensities, broadening, substitution with appropriate ligands and spin-lattice relaxation. Experimental results shows that there is antiferromagnetic exchange interaction among the three metal ions within M3O core. It is found that these complexes in DMSO, CD3CN, CDl(3) and CD3COCD3 solvents are stable at room temperature and their structures in solution are the same as their crystal ones. However, the complexes decomposed into carboxylic acid, pyridin and metal ions in water. The results may be helpful in guiding synthesis of similar complexes