M 4Au12Ag32(p-MBA)30 (M = Na, Cs) bimetallic monolayer-protected clusters: synthesis and structure

Crystals of M 4Au12Ag32(p-MBA)30 bimetallic monolayer-protected clusters (MPCs), where p-MBA is p-mercaptobenzoic acid and M + is a counter-cation (M = Na, Cs) have been grown and their structure determined. The molecular structure of triacontakis[(4-carboxylatophenyl)sulfanido]dodecagolddotriacontasilver, Au12Ag32(C7H5O2S)30 or C210H150Ag32Au12O60S30, exhibits point group symmetry 3 at 100 K. The overall diameter of the MPC is approximately 28 Å, while the diameter of the Au12Ag20 metallic core is 9 Å. The structure displays ligand bundling and intermolecular hydrogen bonding, which gives rise to a framework structure with 52% solvent-filled void space. The positions of the M + cations and the DMF solvent molecules within the void space of the crystal could not be determined. Three out of the five crystallographically independent ligands in the asymmetric unit cell are disordered over two sets of sites. Comparisons are made to the all-silver M 4Ag44(p-MBA)30 MPCs and to expectations based on density functional theory.