Copper-doped tin clusters can be thermally annealed to much more stable compositions with a substantially higher copper/tin ratio. The annealed clusters are only prominent over a narrow range of compositions: CuSn10-15+, CU2Sn12-18+, CU3Sn15-21+, CU4Sn18-(24)+, and CU5Sn21-(27)+. These compositions are close to those found for WmSin+ clusters, raising the possibility that the CumSn+ clusters have core-shell geometries like those proposed for the WmSin+ clusters. Increasing the number of copper atoms causes a change in the dissociation pattern from the fission processes that are characteristic of semiconductor clusters to the expulsion of individual atoms, which usually occurs for metal clusters. The change in the fragmentation pattern may result because the clusters rich in copper melt before they dissociate, while the pure tin clusters dissociate directly from a solidlike phase.