Abstract The solubilities of [Fe(bpy)3](ClO4)2, [Fe(CN)2(bpy)2], and K2[Fe(CN)4(bpy)] in ethanl–water mixed solvents were measured at 25.0 ± 0.1 °C, and the transfer free energy of each complex from water to a water–ethanol mixed solvent was calculated. From the obtained data, the transfer free energies were split into contributions from 2,2′-bipyridine-solvent, cyano ligand-solvent interaction energies, and electrostatic energies. The ratios of the contributed energy from 2,2′-bipyridine vs transfer free energy of free(non-coordinated) 2,2′-bipyridine are almost constant at about 0.6–0.75 over the whole mole fraction range; this is similar to the case of 1,10-phenanthroline, although 2,2′-bipyridine has a single bond between two pyridine rings and the configuration of non-coordinated 2,2′-bipyridine differs markedly as compared with that of the coordinated one. The contributed energy from the cyano ligand in this work is somewhat smaller than that estimated from an iron(II)–cyano-1,10-phenanthroline mixed-ligand complex system; it is considered that the weaker selective solvation of 2,2′-bipyridine than 1,10-phenanthroline affects the contribution from the neighbouring cyano ligand. That the contribution from the electrostatic energy does not agree with the expected value from the Born equation, is attributed to the difference between the local and bulk dielectric constants resulting from the strong selective solvation of 2,2′-bipyridine by ethanol, where ε and ε w represent the dielectric constant of a mixed solvent and water, respectively.