Robust Gold Nanocluster Protected with Amidinates for Electrocatalytic CO2 Reduction.

The first all-amidinate-protected gold nanocluster [Au28(Ph-form)12](OTf)2 (Ph-form = N,N'-Diphenylformamidine) ( Au28 ) has been synthesized and structurally resolved. Single crystal X-ray diffraction reveals that Au28 has a compact Au4@Au24 tetrahedral core-shell structure of T symmetry, which is fully protected by 12 bridging formamidinate ligands. This cluster is quite robust as indicated by the fact that it can stay intact in solution at 80 °C for 6 d. It exhibits excellent catalytic performance for the electroreduction of CO2 with 96.5% Faradaic efficiency (FE) at -0.57 V and a maximum TOF of 48492 h-1 at -0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au28/CNTs maintains stable potentials at ca. -0.69 V for 40 h with FE(CO)s >91%. A superatomic electron configuration of 1S21P62S21D4 has been clarified by DFT computations, and the strong gold-ligand binding and geometric shell closure account for the superior stability of Au28 .