Atomically resolved Au(52)Cu(72)(SR)(55) nanoalloy reveals Marks decahedron truncation and Penrose tiling surface

Gold-copper alloys have rich forms. Here we report an atomically resolved [Au(52)Cu(72)(p-MBT)(55)](+)Cl(−) nanoalloy (p-MBT = SPh-p-CH(3)). This nanoalloy exhibits unusual structural patterns. First, two Cu atoms are located in the inner 7-atom decahedral kernel (M(7), M = Au/Cu). The M(7) kernel is then enclosed by a second shell of homogold (Au(47)), giving rise to a two-shelled M(54) (i.e. Au(52)Cu(2)) full decahedron. A comparison of the non-truncated M(54) decahedron with the truncated homogold Au(49) kernel in similar-sized gold nanoparticles provides for the first time an explanation for Marks decahedron truncation. Second, a Cu(70)(SR)(55) exterior cage resembling a 3D Penrose tiling protects the M(54) decahedral kernel. Compared to the discrete staple motifs in gold:thiolate nanoparticles, the Cu-thiolate surface of Au(52)Cu(72) forms an extended cage. The Cu-SR Penrose tiling retains the M(54) kernel’s high symmetry (D(5h)). Third, interparticle interactions in the assembly are closely related to the symmetry of the particle, and a “quadruple-gear-like” interlocking pattern is observed.