Inorganic Chemistry, Vol.59, No.13, 8836-8845, 2020
Synthesis, Structures, and Photoluminescence of Elongated Face-Centered-Cubic Ag-14 Clusters Containing Lipoic Acid and Its Amide Analogue
Three face-centered-cubic (fcc) silver clusters-namely, [Ag-14(LA)(2)(HLA)(4)(PPh3)(8)](2-) (1), [Ag-14(HLA)(6)(PPh3)(8)] (2), and [Ag-14(NLA)(6)(PPh3)(8)] (3)-that are coprotected by lipoic acid (or its amide derivative) and phosphine ligands have been synthesized and structurally characterized (HLA = (+/-)-alpha-lipoic acid, LA = (+/-)-alpha-lipoate, and NLA = D,L-6,8-thioctamide). These clusters possess two superatomic electrons (the Jellium model), in harmony with a bonding octahedral Ag-6 core capped with 8 Ag atoms. Alternatively, the metal framework of 1-3 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 3 with complex temperature-dependent emission patterns and efficiencies.