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.