Electronic structure of a NHC-protected electron-rich non-superatomic copper nanocluster

• The Cu 23 cluster core exhibits an unprecedented oblate structure • The Cu 23 cluster core has three non-conventional favored electron counts • The whole cluster architecture has a favored electron count of 22 • NHC ligands favor stabilizing Cu nanoclusters with nearly zero oxidation state The electronic structure of a nanocluster, isolated as an impurity and tentatively identified as [Cu 23 (PMe 3 ) 2 (Me 2 I i Pr) 10 ] (Me 2 I i Pr = 1,3-bis(isopropyl)-imidazol-4,5-dimethyl-2-ylidene) is investigated through DFT calculations. The unprecedented non-spherical D 5d structure of the Cu 13 @Cu 10 core of this cluster is shown to be favored for three non-superatomic closed-shell electron counts, namely 14, 18 and 22. With respect to the ligated species, calculations indicate that it is likely to be a 22-electron [Cu 23 (PMe 3 ) 2 (NHC) 10 ] + cation or possibly a monohydride [Cu 23 (PMe 3 ) 2 (NHC) 10 (H)]. Calculations performed on related hypothetical structures indicate that NHC ligands are prone to stabilize electron-rich copper nanoclusters in which the average Cu oxidation state is close to zero.