A mixed oxidation-state (Rh
24+ and Rh
25+) compound, [{Rh
2(acam)
4}
2I]
n·6
nH
2O (Hacam = acetamide), has been synthesized. The compound has a nonpenetrating diamondoid arrangement of {Rh
2(acam)
4} units linked by
4-iodides. All of the dirhodium units are crystallographically equivalent, as are all of the iodide atoms. The magnetic susceptibility of this compound shows that one-half of the Rh
2 units are in the Rh
25+ oxidation state with one odd electron and the other half in the closed-shell Rh
24+ state. Its electrical conductivity is 1.4 × 10
-3 S cm
-1 (pellets, room temperature) and oscillates over the range of 10
5 orders of magnitude during dehydration-rehydration cycles of interstitial water molecules.