Vertex and Edge Truncated Octahedron Gold Crystals. N-alkylimidazole and Silver(I) Ion Controlled Morphology Transformation

Two interesting morphology transformations of Au crystals are observed through reacting a mixture of N-alkylimidazole (denoted as Cn-im, where Cn = CnH2n+1, and n = 18 and 1), AgNO3, and HAuCl4 at 200 °C. The long chain C18-im with increasing AgNO3 concentration leads to a progressive truncation of octahedrons at {100} vertices to produce cubes. On the other hand, increasing the concentrations of C1-im and AgNO3, results in a progressive truncation of octahedrons at {110} edges to give rhombic dodecahedrons, which further transform to the unprecedented tetrahexahedrons. The phenomenon could be understood by considering that while both C18-im and C1-im function as a capping agent with preferential adsorption on Au {111} facets, Ag+ adsorbs and is subsequently reduced to Ag on Au {110} facets for the sterically demanding C18-im, but on the Au {100} facets for C1-im. The competition between the growth of the facets protected by imidazole and Ag controls the morphology transformation via truncation of octahed...