Synthesis, Structures, and Photoluminescence of Elongated Face-Centered-Cubic Ag Clusters Containing Lipoic Acid and Its Amide Analogue.

Three face-centered-cubic (fcc) silver clusters-namely, [Ag(LA)(HLA)(PPh)] (), [Ag(HLA)(PPh)] (), and [Ag(NLA)(PPh)] ()-that are coprotected by lipoic acid (or its amide derivative) and phosphine ligands have been synthesized and structurally characterized (HLA = (±)-α-lipoic acid, LA = (±)-α-lipoate, and NLA = d,l-6,8-thioctamide). These clusters possess two superatomic electrons (the Jellium model), in harmony with a bonding octahedral Ag core capped with 8 Ag atoms. Alternatively, the metal framework of - can be described as adopting a face-centered cubic (fcc) structure elongated along one of the 3-fold axes. The 12 S atoms from the six bioligands bridge the 12 edges of the (fcc) cube, forming a distorted icosahedron. The counterions, solvent or guest molecules play an important role in dictating the crystal lattices of the products. This is the first report of atom-precise structures of Ag-lipoic acid (or its derivatives) clusters, paving the way for further study of structure-property relationships of these bioligand protected metal nanoclusters. Photoluminescence was observed for cluster with complex temperature-dependent emission patterns and efficiencies.