Synthetic methods and structural characterization are reported for 11 novel ternary compounds with the general formula RE6Cd23T (RE=La Gd; T=Sn, Sb, Pb, and Bi). Their crystal structures, as revealed by single crystal and powder X-ray diffraction, are of the cubic Zr6Zn23Si structure type (cF120, Fm (3) over barm, Z=4), a filled version of the Th6Mn23 system. No Cd-containing rare-earth metal binaries are known to form with this structure, but the inclusion of small amounts of a third element allows the formation of the interstitially stabilized ternary structures. Temperature dependent de magnetization measurements confirm local-moment magnetism due to RE3+ ground states for Ce, Pr, and Nd.