Reconstituting C-Centered Hexagold(I) Clusters with N-Heterocyclic Carbene Ligands

Ubiquitous intramolecular aurophilic interactions in gold clusters have usually been assigned as the main determinants of their molecular geometry and various properties. By utilizing N-heterocyclic carbene (NHC) ligands instead of phosphine ligands which have been exclusively used, we have developed ligand-specific photophysical properties of C-centered hexagold(I) (C@Au-6) clusters. This account describes the recent development of carbene-protected C @Au-6 clusters. First of all, a strong intramolecular C-H center dot center dot center dot Au interaction was found as a key structural feature of these clusters. These are also present in the newly emerged NHC-gold nanoclusters, but are negligible in the phosphine counterparts. Interestingly, the use of NHC ligands also produces clusters with a nearly identical metal kernel, but their luminescence changes significantly. In addition, a simple extension of the pi-conjugated system of NHCs from imidazolylidene to benzimidazolylidene is expected to produce significant changes in both absorption coefficient and emission wavelength. These results show the promising potential of carbene ligands in character modulation of metal clusters, and may help in the rational design of carbene ligands for constructing functional metal clusters.

Automated summary

The use of N-heterocyclic carbene (NHC) ligands instead of phosphine ligands in gold clusters can lead to ligand-specific photophysical properties, with intramolecular C-H···Au interactions as a key structural feature. NHC ligands produce clusters with nearly identical metal kernels but significantly different luminescent properties compared to phosphine ligands. Extension of the pi-conjugated system of NHCs can result in significant changes in absorption coefficient and emission wavelength.