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 [Cu(13){S(2)CNR(2)}(6){C[triple bond, length as m-dash]CR′}(4)](PF(6)), 1a–d (where a: R = (n)Bu, R′ = CO(2)Me; b: R = (n)Bu, R′ = CO(2)Et; c: R = (i)Pr, R′ = CO(2)Et; d: R = (n)Pr, R′ = 3,5-(CF(3))(2)C(6)H(3)); [Cu(12)(μ(12)-S){S(2)CNR(2)}(6){C[triple bond, length as m-dash]CR′}(4)], 2a–c; [Cu(12)(μ(12)-Cl){S(2)CNR(2)}(6){C[triple bond, length as m-dash]CR′}(4)](PF(6)), 3a–e (where e: R = (n)Bu, R′ = Ph); [Cu(12)(μ(12)-Br){S(2)CN(n)Bu(2)}(6){C[triple bond, length as m-dash]CPh}(4)](PF(6)), 4e; and [Cu(12)(μ(12)-Cl)(μ(3)-Cl){S(2)CN(n)Bu(2)}(6){C[triple bond, length as m-dash]CCO(2)Me}(3)](+)5a. Cluster 1a is the first structurally characterized copper cluster having a Cu(13) 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 Cu(1–)) 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.