Dinuclear class II CoIII/FeII mixed-valence complexes, [LnCoIII(μ-NC)FeII(CN)3L2]m-, where Ln represents a pentadentate macrocycle and L2 a bpy ligand or 2 cyanides, have electronic properties that make them possible sensitizers in dye sensitized solar cells (DSSCs). For this purpose the new complex Na2[{trans-L14COOCoIII(μ-NC)}FeII(CN)5] was prepd. and characterized by the usual methods and its sensitizer properties compared with those of the known [{trans-L15CoIII(μ-NC)}FeII(CN)3(bipy)eq,ax](ClO4). [{Trans-L14COOCoIII(μ-NC)}FeII(CN)5]2- was designed for electron injection from the Co center on MMCT and the [{trans-LnCoIII(μ-NC)}FeII(CN)3(bipy)]+ structure can produce tuned injection from the Fe center via a MLCT electronic state, as described for similar systems. The characterization on solid oxide semiconductor supports was carried out for these 2 complexes and the results were compared with the behavior obsd. in aq. soln. and in solvents of varying polarities. Their use in a DSSC was tested - although a sensitizer response was obsd. for [{trans-L14COOCoIII(μ-NC)}FeII(CN)5]2-, the complex [{trans-L15CoIII(μ-NC)}FeII(CN)3(bipy)eq,ax]+ does not produce any elec. current on illumination. The low efficiency of such a DSSC is due to the low value of the extinction coeff. of the MMCT band responsible for the electron injection and with the small driving force for the redn. of the complex with the std. I2/I3- system used after electron injection.