Basic [Au 25 (SCH 2 CH 2 Py) 18 ] − ⋅Na + Clusters: Synthesis, Layered Crystallographic Arrangement, and Unique Surface Protonation

The synthesis of high‐purity and high‐yield Au 25 clusters protected by the basic pyridyl ethanethiol (HSCH 2 CH 2 Py, 4‐PyET and 2‐PyET) is presented. Single‐crystal X‐ray diffraction of the [Au 25 (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 [Au 25 (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. [Au 25 (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 Au 25 clusters paves the way to realize a new family of metalloid clusters possessing basic properties.