Reactions of SbCl3 and BiCl3 with [(PNBut)2(NRLi·THF )2] (R 4;= 4;But, Ph) produced polycyclic cage complexes of the formula {[(PNBut)2(NR)2E]Cl}, (E 4;= 4;Sb, R 4;= 4;But 1a; E 4;= 4;Bi, R 4;= 4;But 2; E 4;= 4;Sb, R 4;= 4;Ph 3). The bis(tert-butylamido)cyclodiphosphazane complexes of antimony were further derivatized by the substitution of the chloride ligand with N3 1b, -OPh 1c, and N(SiMe3)2 1d groups. Structural studies showed all compounds to have virtually isometric central polycyclic cages. In solution some of these complexes are fluxional, due to the heavier Group 15 elements pyramidal inversion between two equivalent cyclodiphosphazane ring sites. The activation energies for this process were determined to be a function of both metal and ligand.