Synthesis and structural characterization of inverse-coordination clusters from a two-electron superatomic copper nanocluster.

We have synthesized and structurally characterized a series of centred cuboctahedral copper clusters, namely [Cu13 {S2 CNR2 }6 {C[triple bond, length as m-dash]CR'}4 ](PF6 ), 1a-d (where a : R = n Bu, R' = CO2 Me; b : R = n Bu, R' = CO2 Et; c : R = i Pr, R' = CO2 Et; d : R = n Pr, R' = 3,5-(CF3 )2 C6 H3 ); [Cu12 (μ12 -S){S2 CNR2 }6 {C[triple bond, length as m-dash]CR'}4 ], 2a-c ; [Cu12 (μ12 -Cl){S2 CNR2 }6 {C[triple bond, length as m-dash]CR'}4 ](PF6 ), 3a-e (where e : R = n Bu, R' = Ph); [Cu12 (μ12 -Br){S2 CN n Bu2 }6 {C[triple bond, length as m-dash]CPh}4 ](PF6 ), 4e ; and [Cu12 (μ12 -Cl)(μ3 -Cl){S2 CN n Bu2 }6 {C[triple bond, length as m-dash]CCO2 Me}3 ]+ 5a . Cluster 1a is the first structurally characterized copper cluster having a Cu13 centered cuboctahedral arrangement, a miniature of the bulk copper fcc structure. Furthermore, the partial Cu(0) character in the 2-electron superatoms 1 was confirmed by XANES. Inverse coordination clusters 2-5 are the first examples of copper clusters containing main group elements (Cl, Br, S) with a hyper-coordination number, twelve. A combined theoretical and experimental study was performed, which shows that the central copper (formally Cu1- ) in nanoclusters 1 can be replaced by chalcogen/halogen atoms, resulting in the formation of clusters 2-5 which show enhanced luminescence properties and increase in the ionic component of the host-guest interaction as Br ≈ Cl > S > Cu, which is consistent with the Cu-X Wiberg indices. The new compounds have been characterized by ESI-MS, 1 H, 13 C NMR, IR, UV-visible, emission spectroscopy, and the structures 2a-b , 3d-e , 4e and 5a were established by X-ray diffraction analysis.