The reaction of [N(PPh3)2][CpCo(CN)3] and [Cb*Co(NCMe)3]PF6 (Cb* = C4Me4) in the presence of K+ afforded {K⊂[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⊂[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 μ-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 FcPF6 produced paramagnetic (S = 4/2) [Co8]4+, releasing Cs+ or K+. The oxidation-induced dissociation of M+ from the cages is chemically reversed by treatment of [Co8]4+ and CsOTf with 4 equiv of Cp2Co. Cation recognition by [Co8] and [Rh4Co4] cages was investigated. Electrochemical measurements indicated that E1/2(Cs+) - E1/2(K+) ∼ 0.08 V for [MCo8+. [ABSTRACT FROM AUTHOR]