Basic [Au25 (SCH2 CH2 Py)18 ]- ⋅Na+ Clusters: Synthesis, Layered Crystallographic Arrangement, and Unique Surface Protonation.

The synthesis of high-purity and high-yield Au25 clusters protected by the basic pyridyl ethanethiol (HSCH2 CH2 Py, 4-PyET and 2-PyET) is presented. Single-crystal X-ray diffraction of the [Au25 (4-PyET)18 ]- ⋅Na+ clusters has revealed a structure similar to that known for the phenyl ethanethiolate analogue, but with pyridyl-N coordination to Na+ , a more relaxed ligand shell, and a profoundly layered arrangement in the solid state. Because of the pendant Py moiety, the [Au25 (PyET)18 ]- clusters are endowed with unique (de)protonation equilibria, which has been characterized in detail by UV/Vis absorption and 1 H NMR spectroscopy. [Au25 (PyET)18 ]- clusters showed an unexpectedly H+ -dependent solubility that is tunable in aqueous and organic solvents. The successful synthesis of the basic Py-terminated thiolate-protected Au25 clusters paves the way to realize a new family of metalloid clusters possessing basic properties.