Octametallic (L)(8)Ln(8)E(6)(EPh)(12) clusters (L = Lewis base; Ln = lanthanide ion; E = S, Se; EPh = SPh, SePh) can be prepared either by the reduction of Se-C bonds with low-valent Ln or by the reaction of Ln(SePh)(3) with elemental E. Because all possible ligand sites (i.e., L, E, EPh) are reactive, the ligands can be varied systematically to further the understanding of structure/property relationships. Chalcogenolate ligands can be selectively varied, as in the reaction of (THF)(8)Sm8Se6(SePh)(12) with PhSSPh to form (THF)(8)Sm8Se6(SPh)(12). Neutral L can be altered without disrupting structure, as in the replacement of THF with pyridine to give (py)(8)Sm8Se6(SePh)(12). Even chalcogenido ligands can be chemically replaced: the reaction of (THF)(8)Sm8Se6(SPh)(12) with elemental S gives the all-sulfur cluster (THF)(8)Sm8S6(SPh)(12). All compounds were isolated and characterized by IR and UV-visible spectroscopy and by low-temperature single-crystal X-ray diffraction to confirm that the structures contain cubes of Ln(III) ions with E2- capping the faces and EPh bridging the edges of the cube. The Sm8Se6(EPh)(12) clusters are intensely colored because of a Se2- to Sm(III) charge transfer absorption, while the sulfide clusters exhibit the light yellow color characteristic of Sm(III) complexes. The light green Nd complex (py)(8)Nd8Se6(SePh)(12) was isolated from the reaction of Nd(SePh)3 with Se to confirm that chalcogenolate displacement is general to the redox-inactive lanthanides and that the intense colors of the Sm selenido clusters are related to the redox activity of the Ln. The two pyridine complexes (py)(8)LnSe(6)(SePh)(12) (Ln = Nd, Sm) are isostructural. Crystal data (Mo K alpha, 153(2) K) are as follows. (THF)(8)Sm8Se6(SPh)(12): triclinic space group P (1) over bar, a 17.637(7) Angstrom, b = 18.337(5) Angstrom, c = 20.466(12) Angstrom, alpha 103.03(4)degrees, beta= 94.71(4)degrees, gamma = 94.28(3)degrees, Z = 2. (py)(8)Sm8Se6(SePh)(12): monoclinic space group C2/m, a 18.770(2) Angstrom b = 28.113(4) Angstrom, c 16.461(3) Angstrom, beta = 120.65(1)degrees, Z = 2. (THF)(8)Sm8S6(SePh)(12): orthorhombic space group Pcab, a = 19.803(3) Angstrom, b = 22.446(3) Angstrom, c = 26.072(4) Angstrom, Z = 8.