The M枚ssbauer spectra of all solid solutions Y[Fe1鈭?/sub>xCox(CN)6]路4H2O present quadrupolar splittings with negative isomer shifts values due to the existence of a strong 蟺 back-bonding effect from the Fe3+ ion towards the CN ligands. All compounds follow the Curie-Weiss law showing anti-ferromagnetic interactions at very low temperatures.