Ligand accommodation causes the anti-centrosymmetric structure of Au(13)Cu(4)clusters with near-infrared emission

摘要

We synthesized an [Au13Cu4(PPh3)(4)(SPy)(8)](+)nanocluster co-capped by phosphine and thiolate ligands. Interestingly, this Au(13)Cu(4)cluster corresponds to an anti-centrosymmetric structure with the four copper atoms coordinated to the mixed ligands on the same side of the Au(13)icosahedron, which is in sharp contrast to the [Au13Cu4(PPh2Py)(4)(SPhtBu)(8)](+)and [Au13Cu2(PPh3)(6)(SPy)(6)](+)clusters which possess highly symmetric structures with well-separated Cu adatoms. Both [Au13Cu4(PPh3)(4)(SPy)(8)](+)and [Au13Cu2(PPh3)(6)(SPy)(6)](+)clusters correspond to 8 valence electron superatoms with large HOMO-LUMO gaps, respectively. The difference in structure is rooted in the nature of the mixed ligands, with the bidentate SPy binding strongly to Cu on both binding sites (-N-Cu and Au-SR-Cu) leading to the co-linking of adjacent Cu atoms, while the bidentate PPh2Py binds Cu on one site and Au on the other giving rise to a separation of the Cu atoms even in the presence of relatively higher monomer concentration. Both [Au13Cu4(PPh3)(4)(SPy)(8)](+)and [Au13Cu2(PPh3)(6)(SPy)(6)](+)display emissions in the near-IR regions. TD-DFT calculations reproduce the spectroscopic results with specified excited states, shedding light on the geometric and electronic behaviors of the ligand-protected Au(13)M(x)clusters.