Synthesis. As a cluster-catalyst support, we selected the metal organic framework NU1K (NU-1000; Figure ). (Recall that MOFs, including NU1K, are extended porous solids; only a tiny, illustrative portion is shown.) Like many MOFs, NU1K displays a sizable internal surface array: ~2,200 m 2 g -1 -roughly twice that of the highest area zeolite and comparable to many high-area porous carbon formulations. As a broad class, MOFs offer regularity/periodicity of void spaces, tunability of pore sizes, and adjustability of pore surface (interior surface) properties. Zr-MOFs, including NU1K, have been shown to be stable under a wide range of thermal and chemical conditions. NU1K ideally is composed of Zr6(μ3-O)4(μ3-OH)4(H2O)4(OH)4 nodes and tetratopic 1,3,6,8-(pbenzoate)pyrene (TBAPy 4-) linkers. However, depending on the specifics of its activation (i.e., removal of synthesis solvent and growth modulators), up to 75% of the nonstructural aqua + hydroxo node-ligand pairs may be adventitiously displaced by bridging formate anions. The activation procedure used (see Supplemental Information) leaves the material with multiple formate ligands per node. Independent of formate content, NU1K offers 1D hexagonal and triangular channels of diameters ∼31 Å and ∼12 Å, respectively, as well as cross-connecting pores (termed c-pores) of just under 10 Å diameter (Figure ). Having previously studied in detail the installation, siting, and resistance to migration of the Anderson POM, RhMo6O24 n-, we started with a closely similar POM, (NH4)3[H6CoMo6O24]•7H2O (denoted as CoMo6O24) (Figure ). This POM comprises a {CoO6} octahedron connected to six {MoO6} octahedra in an edge-sharing mode, to form a planar, disk-like cluster (Figure ). The dimensions of CoMo6O24 are approximately 8.55 Å × 8.55 Å × 3.15 Å, which fit well within the c-pore of NU1K. We successfully encapsulated CoMo6O24 via impregnation from aqueous solution; the resulting hybrid material we refer to as CoMo6O24@NU1K.