Robust Gold Nanocluster Protected With Amidinates For Electrocatalytic Co2 Reduction

The first all-amidinate-protected gold nanocluster [Au-28(Ph-form)(12)](OTf)(2) (Ph-form=N,N '-diphenylformamidinate) (Au-28) has been synthesized and structurally resolved. Single crystal X-ray diffraction reveals that Au-28 has a compact Au-4@Au-24 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 degrees 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 1731 h(-1) at -0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au-28/CNTs maintains stable potentials at ca. -0.69 V for 40 h with FE(CO)s>91 %. A superatomic electron configuration of 1S(2)1P(6)2S(2)1D(4) has been clarified by DFT computations, and the strong gold-ligand binding and geometric shell closure account for the superior stability of Au-28.