The reaction of [N(PPh3)(2)][CpCo(CN)(3)] and [Cb*Co(NCMe)(3)]PF6 (Cb* = C4Me4) in the presence of K+ afforded {K subset of[CpCo(CN)(3)](4)[Cb*Co](4)}PF6, [KCo8]PF6. IR, NMR, ESI-MS indicate that [KCo8]PF6 is a high-symmetry molecular box containing a potassium ion at its interior. The analogous heterometallic cage {K subset of[Cp*Rh(CN)(3)](4)[Cb*Co](4)}PF6 ([KRh4Co4]PF6) was prepared similarly via the condensation of K[Cp*Rh-(CN)(3)] and [Cb*Co(NCMe)(3)]PF6. Crystallographic analysis confirmed the structure of [KCo8]PF6. The cyanide ligands are ordered, implying that no Co-CN bonds are broken upon cage formation and ion complexation. Eight Co-CN-Co edges of the box bow inward toward the encapsulated K+, and the remaining four mu-CN ligands bow outward. MeCN solutions of [KCo8](+) and [KRh4Co4](+) were found to undergo ion exchange with Cs+ to give [CsCo8](+) and [CsRh4Co4](+), both in quantitative yields. Labeling experiments involving [(MeC5H4)Co(CN)(3)](-) demonstrated that Cs+-for-K+ ion exchange is accompanied by significant fragmentation. Ion exchange of NH4+ with [KCo8](+) proceeds to completion in THF solution, but in MeCN solution, the exclusive products were [Cb*Co(NCMe)(3)]PF6 and the poorly soluble salt NH4CpCo(CN)(3). The lability of the NH4+-containing cage was also indicated by the rapid exchange of the acidic protons in [NH4Co8](+). Oxidation of [MCo8](+) with 4 equiv of FcPF(6) produced paramagnetic (S = 4/2) [Co-8](4+), releasing Cs+ or K+. The oxidation-induced dissociation of M+ from the cages is chemically reversed by treatment of [Co-8](4+) and CsOTf with 4 equiv of Cp2Co. Cation recognition by [Co-8] and [Rh4Co4] cages was investigated. Electrochemical measurements indicated that E-1/2(Cs+) - E-1/2 (K+) similar to 0.08 V for [MCo8](+).