This paper describes the formation of cobalt and iron metal nanoclusters in various polymeric domains. The size of the particles, their size distribution and their geometry is controlled by the extent of the interfacial interactions between the polymeric phase and the growing metal fragments. Iron oxide particles are shown to exhibit various geometries as a function of the polymer medium and the temperature at which they are formed. The selective phase separation and particle confinement of cobalt clusters in the presence of PS25300-b-PMMA25900 block co-polymer was achieved due to the different reactivities of the functional groups in the blocks towards the metal fragments. Transmission electron micrographs showed that cobalt clusters aggregated primarily in the poly(methyl methacrylate) block, while no cobalt nanoclusters were observed in the polystyrene block, thus creating a patterned distribution that coincided with the morphology of the block copolymer.