Basic [Au₂₅(SCH₂CH₂Py)₁₈]⁻⋅Na⁺ Clusters: Synthesis, Layered Crystallographic Arrangement, and Unique Surface Protonation

Abstract

The synthesis of high‐purity and high‐yield Au25 clusters protected by the basic pyridyl ethanethiol (HSCH2CH2Py, 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 1H 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.