Hybrid bimetallic-TTF materials in which the organic layer adopts an unprecedented dimerized structure and the inorganic layer is formed by the first ferromagnetic Cr-III-Mn-II-Cr-III complex are reported. These materials provide valuable information on the magnetic interactions between these metal ions which should help in the understanding of the behavior of extended magnetic lattices based on oxalate complexes. A method is also provided to prepare materials combining the ferromagnetic properties of the bimetallic oxalate network with the conducting properties of the TTF-type donors.