Reaction of [(CpFe)-Fe-x(eta(5)-P-5)] (Cp-x = eta(5)-C5Me5 (1a), eta(5)-C5Me4Et (1b)} with CuBr leads to the fullerene-like nanoballs [((CpFe)-Fe-x (eta(5): eta(1): eta(1): eta(1): eta(1): eta(1)-P-5)}(12) {CuBr)(10 {)Cu2Br3)(5) {Cu-(CH3CN)(2)}(5)} {Cp-x = eta(5)-C5Me5 (5a), eta(5)-C5Me4Et (5b)) comprising a cluster core of 90 non-carbon atoms. In contrast to previous results by variation of stoichiometry and concentration conditions, the formation of polymeric product was hindered, and exclusive formation of the spherical cage compound was achieved. The cluster 5b possesses an inside diameter of 1.29 nm and an outside diameter of 2.37 nm. Definitive evidence for encapsulation of a [CpxFe(eta(5)-P-5)1 unit (1b) within the inner cavity of the nanocluster 5b is shown by Xray crystallographic results. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.