[Ag20{S2P(OR)2}12]: A Superatom Complex with a Chiral Metallic Core and High Potential for Isomerism

The synthesis and structural determination of a silver nanocluster [Ag-20{S2P(OiPr)(2)}(12)] (2), which contains an intrinsic chiral metallic core, is produced by reduction of one silver ion from the eight-electron superatom complex [Ag-21{S2P(OiPr)(2)}(12)](PF6) (1) by borohydrides. Single-crystal X-ray analysis displays an Ag-20 core of pseudo C-3 symmetry comprising a silver-centered Ag-13 icosahedron capped by seven silver atoms. Its n-propyl derivative, [Ag-20{S2P(OnPr)(2)}(12)] (3), can also be prepared by the treatment of silver(I) salts and dithiophosphates in a stoichiometric ratio in the presence of excess amount of [BH4](-). Crystal structure analyses reveal that the capping silveratom positions relative to their icosahedral core are distinctly different in 2 and 3 and generate isomeric, chiral Ag-20 cores. Both Ag-20 clusters display an emission maximum in the near IR region. DFT calculations are consistent with a description within the superatom model of an 8-electron [Ag-13](5+) core protected by a [Ag-7{S2P(OR)(2)}(12)](5-) external shell. Two additional structural variations are predicted by DFT, showing the potential for isomerism in such [Ag-20{S2P(OR)(2)}(12)] species.