Interplay of structural and electronic stabilizing factors in neutral and cationic phosphine protected Au13 clusters

Stable ligand protected sub-nanometer metal clusters exist as different structural isomers which mainly differ by the geometry of the metal core. The structural and electronic properties of the bare and phosphine protected gold, Au-13, clusters were theoretically investigated in order to elucidating the relation between different metal core geometries, electronic structures and the stability of the complex. For neutral and low (3+) charged bare clusters, bilayers and flake geometries are computed to be more stable than the icosahedral geometry while for the cation 5+ the most stable metal core exhibits a regular icosahedral geometry. Flake geometries are composed of edge-fused gold tetrahedron motifs and triangular rings. The binding with phosphine induces their stabilization with respect to the bilayer and icosahedral structures. Unexpectedly, the stabilization of the ligated flake geometry with respect to the compact icosahedral-based core increases with the positive overall charge of the complex, being maximum for the highly charged species [Au-13(PH3)(10)](5+). The origin of the stability is explained in connection with electronic structure and the charge transfer induced by the ligand shell. The distribution of the spin density of the neutral Au-13(PH3)(12) with a flat cage metal core is characterized.