A family of nanoscale-sized supramolecular cage compounds with a trigonal prismatic framework was prepared by means of spontaneous self-assembly from the combination of a predesigned molecular ''clip'' with tritopic pyridyl subunits. As confirmed by x-ray crystallography, the smallest structure of the reported series is Ϸ1 ؋ 2 nm and possesses a nitrate anion incarcerated inside its molecular cavity. The largest structure has dimensions of Ϸ 1 ؋ 4 nm. T he formation of discrete supramolecular entities driven and held together by metal coordination is an intense new area of investigation at the forefront of supramolecular chemistry (1-10). Because self-assembly is guided by the chemical information encoded into the molecular subunits, diverse structures with predetermined shape, size, and functionality can readily be designed. Indeed, a wide variety of aesthetic structures have been realized, such as molecular grids, helicates, rings, catenanes, tetrahedra, cubes, cuboctahedra, etc. Once assembled, many of the hollow structures have been shown to be capable of encapsulating molecules through electrostatic and͞or dispersion forces. Often times, ions will template the formation of an assembly (11-21). When considering that metal-containing assemblies often possess magnetic, photophysical, and͞or redox properties not accessible from purely organic systems, studies in basic host-guest chemistry hold new promise for technologies in molecular sensing (22-28), separations, and catalysis (29,30).Because lower-symmetry hosts can ultimately be expected to show enhanced guest selectivity, especially toward planar aromatic guests, prismatic cages represent a natural progression in the development of this area. Although M 3 L 2 -type cages are relatively simple three-dimensional constructs, they remain uncommon. Of those that have been reported (31-40), most usually either require the use of templates to assemble in solution, or assemble only in the solid state. Part of the reason for this limitation is possibly the fact that, in most cases, flexible ligands were used. By contrast, structures derived from rigid tritopic linkers with cis-metal ions are either: (i) tetrahedral M 6 L 4 cages (41) where L is a planar ligand, or (ii) double-square M 6 L 4 cages (42) where L is a 109°linker ligand. Construction of the M 3 L 2 , D 3h species is complicated by the fact that rigid tritopic linkers with ideal mutual angles of 60°are not easily accessible. A noteworthy trigonal bipyramidal structure (35), made from Pd(II) ions and a calix[3]arene subunit, was shown to be able to reversibly bind a molecule of C 60 .By exploiting incommensurate symmetry requirements for differing metallic subunits, an alternative approach to structures of this general topology was recently reported. Raymond and Wong (43-45) successfully prepared a series of M 2 MЈ 3 L 6 supramolecular clusters where a multifunctionalized ligand (L) was cleverly designed to selectively interact with two types of metal ions (one hard and one soft).Double oxidative addition ...