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N-heterocyclic carbene-functionalized magic-number gold nanoclusters

Abstract

Magic-number gold nanoclusters are atomically precise nanomaterials that have enabled unprecedented insight into structure–property relationships in nanoscience. Thiolates are the most common ligand, binding to the cluster via a staple motif in which only central gold atoms are in the metallic state. The lack of other strongly bound ligands for nanoclusters with different bonding modes has been a significant limitation in the field. Here, we report a previously unknown ligand for gold(0) nanoclusters—N-heterocyclic carbenes (NHCs)—which feature a robust metal–carbon single bond and impart high stability to the corresponding gold cluster. The addition of a single NHC to gold nanoclusters results in significantly improved stability and catalytic properties in the electrocatalytic reduction of CO2. By varying the conditions, nature and number of equivalents of the NHC, predominantly or exclusively monosubstituted NHC-functionalized clusters result. Clusters can also be obtained with up to five NHCs, as a mixture of species.

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Fig. 1: Synthesis and characterization of NHC-modified Au11 nanoclusters.
Fig. 2: DFT and UV–vis spectroscopic prediction of structure for NHC-modified nanoclusters.
Fig. 3: Spectroscopic and XRD characterization of NHC-substituted cluster 3a.
Fig. 4: Assessment of stability and ligand dissociation by CID mass spectrometry.
Fig. 5: Nanocluster stability and activity in the electrocatalytic reduction of CO2 to CO.

Data availability

Spectral and purity data are available for all new compounds, along with original NMR, MS, XPS, UV–vis, DFT, TGA–MS and electrochemical data. Single-crystal X-ray crystallographic data are included for cluster 3a, while crystallographic data for cluster 3a have been deposited at the Cambridge Crystallographic Data Centre under deposition no. CCDC 1878623. Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. All other data supporting the findings of this study are available within the Article and its Supplementary Information, or from the corresponding author upon reasonable request.

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Acknowledgements

C.M.C., J.H.H. and E.H.S. acknowledge support from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation (CFI) and the Ministry of Research Innovation (MRI) in terms of discovery grants and infrastructure grants, respectively. K.A. and P.J.G. thank NSERC for support through the awarding of USRA fellowships. M.R.N. thanks the Ontario Graduate Scholarship programme and Queen’s University for fellowship support. This work was supported by KAKENHI from the Japan Society for the Promotion of Science (JSPS; 17H03030 and 16K13962 to C.M.C. and 17H01182 to T.T.), Nanotechnology Platform (project no. 12024046) and the Elements Strategy Initiative for Catalysts & Batteries (ESICB). J.S.P.S. and N.U. acknowledge funding of this research through The World Premier International Research Center Initiative (WPI) programme. The computational work was supported by the Academy of Finland through the Academy Professorship of H.H. All computations were carried out at the Finnish CSC computer centre. S.K. thanks the Väisälä Foundation for a personal PhD study grant. K. Itami is thanked for assistance with the preparation of this manuscript.

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C.M.C., P.J.U., M.R.N. and K.S. designed and carried out the synthesis of the nanoclusters, assisted by K.A., P.J.G., M.N., K.M.O. and R.W.Y.M. K.M.O. and R.W.Y.M. optimized the synthetic procedures and purifications and acquired TGA–MS data. MS analysis was performed and interpreted by S.T., R.T. and T.T., including CID MS. Crystallization of 3a was carried out by M.N. and S.T. on a sample prepared and purified by K.M.O. DFT studies, including prediction of structure and optical spectra, were carried out by S.K., S.M. and H.H. EXAFS and XANES studies were carried out and interpreted by J.H.H. and J.D.P. Electrocatalytic studies were performed and interpreted by C.-T.D. and E.H.S. The manuscript was written by C.M.C. with assistance from co-authors.

Corresponding authors

Correspondence to Hannu Häkkinen or Tatsuya Tsukuda or Cathleen M. Crudden.

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Supplementary information

Supplementary information

Supplementary experimental details, synthetic procedures, compound characterization data including spectral and purity data for all new compounds, along with original NMR, MS, XPS, UV-vis DFT, TGA–MS, single-crystal X-ray analysis and electrochemical data.

Crystallographic data

CIF for compound 3a; CCDC reference: 1878623.

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Narouz, M.R., Osten, K.M., Unsworth, P.J. et al. N-heterocyclic carbene-functionalized magic-number gold nanoclusters. Nat. Chem. 11, 419–425 (2019). https://doi.org/10.1038/s41557-019-0246-5

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