Synthesis of shaped Pt nanoparticles using common anions or small molecules as shape-directing agents: observation of a strong halide or pseudo-halide effect

Chemical reduction of Pt(II) and Pt(IV) salts by H-2, hydrazine, or borohydride ion, in the presence of common anions or small molecules is surveyed to discover shape-directing agents suitable for selective formation of Pt metal nanocubes or nanotetrahedra. Surfactants tested include a variety of amino acids, HSCH2CO2H, Ph2PCH2CO2H, polycarboxylate species, such as glycolate or tartrate ion, and several common anions (including CF3SO3-, ClO4-, NO3-, CO32-, PO43-, SO42-, Cl-, Br-, or I-). Although carboxylate, chloride, bromide, carbonate, nitrate, perchlorate, phosphate, sulfate, or triflate ions show poor shape-directing influence, the presence of hydroxide and iodide ions gives an unexpected halide (or pseudo-halide) effect. Hydrogen reduction of [Pt(OH)(6)](2-) ion at basic pH gives high yields of cubic Pt nanoparticles, while hydrogen reduction of [PtI6](2-) ion at basic pH gives high yields of tetrahedral Pt nanoparticles.