The Structure and Bonding of Au25(SR)18 Nanoclusters from EXAFS: The Interplay of Metallic and Molecular Behavior

While recent advances in the synthesis and crystallography of gold–thiolate nanoclusters have led to enormous progress in understanding the structure and bonding of gold thiolate nanomaterials, the changes in structure experienced by these nanomaterials in different conditions, such as low temperature and solvation, is still largely lacking. Herein, we report a temperature- and solvation-dependent extended X-ray absorption fine structure (EXAFS) study of thiolate-protected Au25 nanoclusters. The structural changes experienced by Au25 in response to low temperature and different solvation environments are illustrated in great detail using a site-specific EXAFS fitting approach consisting of one Au–S and three Au–Au shells. EXAFS simulations as well as ab initio calculations of the local density of states are used to support the EXAFS analysis and correlate the structural characteristics of Au25 with its electronic properties. These experimental and theoretical studies point out the existence of the interplay between the “metallic” behavior of the Au13 core and the “molecular” behavior of the six RS–Au–S(R)–Au–SR “staple” units within Au25, which may shed light on its catalytic mechanism and aid in the design and synthesis of other gold–thiolate nanoclusters by balancing the metallic and molecular interactions.