Controlling gold nanoclusters by diphospine ligands.

We report the synthesis and structure determination of a new Au22 nanocluster coordinated by six bidentate diphosphine ligands: 1,8-bis(diphenylphosphino) octane (L(8) for short). Single crystal X-ray crystallography and electrospray ionization mass spectrometry show that the cluster assembly is neutral and can be formulated as Au22(L(8))6. The Au22 core consists of two Au11 units clipped together by four L(8) ligands, while the additional two ligands coordinate to each Au11 unit in a bidentate fashion. Eight gold atoms at the interface of the two Au11 units are not coordinated by any ligands. Four short gold-gold distances (2.64-2.65 Å) are observed at the interface of the two Au11 clusters as a result of the clamping force of the four clipping ligands and strong electronic interactions. The eight uncoordinated surface gold atoms in the Au22(L(8))6 nanocluster are unprecedented in atom-precise gold nanoparticles and can be considered as potential in situ active sites for catalysis.