A bowl-shaped calixresorcinarene, 1, has been derivatized to incorporate four phosphonite units to give a phosphonitocavitand, 2, which can act as a tetradentate ligand. Thus, 2 has been used in the synthesis of several tetracopper(I) and tetrasilver(I) complexes, such as [PyH](+)[2 . Cu-4(mu-Cl)(4)(mu(3)-Cl)](-) (4) and [PyH](+)[2 . Ag-4(mu-Cl)(4)(mu(4)-Cl)](-) (5). The tetracopper(I) complex, 4, and tetrasilver(I) complex, 5, have been shown to act as size-selective hosts for halide inclusion. Iodide is preferred over chloride as guest in 4 since it is large enough to coordinate to all four copper atoms in an unusual mu(4)-face-bridging bonding mode. The anion inclusions found for the transition metal rimmed bowl complexes are unique in supramolecular chemistry. The anion occluded complex 5a can act as a nucleophile to convert RI to RCl; the reaction occurs in high yield, follows the reactivity sequence t-BuI > i-PrI > MeI, and occurs with predominant retention of stereochemistry in the reaction of (S)-(+)-2-iodooctane. The overall reaction leads to the favorable replacement of the occluded mu(3)-Cl ligand in 5a by mu(4)-L.