A Missing Link in Undecagold Cluster Chemistry: Single-Crystal X-ray Analysis of [Au11(PPh3)7Cl3]

Because of quantum-size effects, molecular gold clusters are promising materials for applications in nanoscience and nanotechnology. Owing to the feasible synthesis of Au-11 species out of [Au(PPh3)Cl], this material is the subject of many investigations, although its full crystal structure including the ligand shell remained unknown. We have been able to obtain the solid-state structure at atomic resolution, even for the cocrystallized solvent molecules: The composition of the red crystals corresponds to [Au-11(PPh3)(7)Cl-3]center dot CH2Cl2 center dot 1.5{(CH3CH2)(2)O}. The gold atoms in the cluster subtend a core of almost C-3v symmetry derived from a centered icosahedron, which is present in most Au-11 species. The mean AuAu distance amounts to 2.8076 angstrom and the mean AuCl distance to 2.3730 angstrom; both are in good agreement with comparable data in structurally characterized gold clusters. The mean core diameter, measured between the centers of the gold atoms of opposite sides of the cluster, is about 4.9 angstrom, and the overall van der Waals diameter can be estimated to 19.8 angstrom. The optical absorbance of [Au-11(PPh3)(7)Cl-3] in solution reveals characteristic peaks at 318 and 406 nm and a shoulder between 450 and 550 nm. The peak at 406 nm and the shoulder can also be resolved for the solid. The energy of the first optically active electron transition of ca. 2.0 eV is very close to the theoretically derived data of the HOMOLUMO gap. In accordance with the literature, only one singlet in the P-31{H-1} NMR spectrum is found at = 52 ppm, even at 80 degrees C.