A series of Fe-S and Fe-Se cubane clusters containing all four combinations of the general formula [Fe4X4(Y-CH3)(4)](2-) (X= S/Se, Y S/Se) is investigated with FTIR and Raman spectroscopy. The terminally selenolate coordinated clusters (Y Se) are prepared by a new synthetic route. All four cluster compounds are structurally characterized by X-ray single-crystal structure determination. Infrared and Raman spectra of all compounds are presented and interpreted with normal coordinate analysis. The corresponding force fields are based on that developed for the Fe4S4-benzyl cluster (Czemuszewicz, R. S.; Macor, K. A.; Johnson, M. K.; Gewirth, A.; Spiro, T. G. J. Am. Chem. Soc. 1987, 109, 7178-7187). An empirical procedure is presented to convert Fe-S into Fe-Se force constants. Only minor changes in force constants are found upon S --> Se exchange, reflecting the similarity of the Fe-S and Fe-Se bonds. The drastic frequency shifts in the metal-ligand region observed upon substitution of sulfur by selenium are, therefore, primarily due to the corresponding mass changes.