Synthesis, Structures, and Photoluminescence of Elongated Face-Centered-Cubic Ag14 Clusters Containing Lipoic Acid and Its Amide Analogue.

Three face-centered-cubic (fcc) silver clusters-namely, [Ag14(LA)2(HLA)4(PPh3)8]2- (1), [Ag14(HLA)6(PPh3)8] (2), and [Ag14(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 = (±)-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 Ag6 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.

Dissection of bicapped octahedral copper hydride cluster to form two chiral tetrahedral copper hydride cluster series exhibiting auto deracemization and photoluminescence.

Three series of copper hydride clusters [Cu8H6L6]2+ (1), [Cu4HX2L4]+ where X- = Cl- (2a), Br- (2b), I- (2c), N3- (2d) and SCN- (2e), and [Cu4HX3L3] where X- = Br- (3b) and I- (3c) (L = 2-(diphenylphosphino)pyridine, dppy) were synthesized and characterized by single-crystal X-Ray crystallography and standard spectroscopic techniques. The metal core of 1, Cu8, can be described as a bicapped octahedron, while those of 2 and 3 series adopt tetrahedral structures. The hydride positions were deduced from difference electron density maps and corroborated by NMR and DFT calculations. For 1, there are two µ4-H-, one each in the two tetrahedral cavities of the two capping atoms and four µ3-H- on the six triangular faces around the waist of the octahedron. For [Cu4HX2L4]+ and [Cu4HX3L3] series, the single µ4-H- resides in the center of the Cu4 tetrahedron. It was found that these three series of copper clusters are intimately connected and can convert from one to another under specific reaction conditions. Their transformation pathways were investigated in detail. Spontaneous resolution to form optically pure enantiomeric single crystals was observed for [Cu4H(SCN)2L4]+ (2e) and [Cu4HBr3L3] (3b). Photoluminescence was observed for [Cu4HX2L4]+, as well as [Cu4HX3L3] with strong emissions from green to yellow regions.