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

Abstract

We have synthesized and structurally characterized a series of centred cuboctahedral copper clusters, namely [Cu₁₃{S₂CNR₂}₆{C[triple bond, length as m-dash]CR'}₄](PF₆), <b>1a-d</b> (where <b>a</b>: R = ^<i>n</i> Bu, R' = CO₂Me; <b>b</b>: R = ^<i>n</i> Bu, R' = CO₂Et; <b>c</b>: R = ⁱPr, R' = CO₂Et; <b>d</b>: R = ^<i>n</i> Pr, R' = 3,5-(CF₃)₂C₆H₃); [Cu₁₂(μ₁₂-S){S₂CNR₂}₆{C[triple bond, length as m-dash]CR'}₄], <b>2a-c</b>; [Cu₁₂(μ₁₂-Cl){S₂CNR₂}₆{C[triple bond, length as m-dash]CR'}₄](PF₆), <b>3a-e</b> (where <b>e</b>: R = ^<i>n</i> Bu, R' = Ph); [Cu₁₂(μ₁₂-Br){S₂CN ^<i>n</i> Bu₂}₆{C[triple bond, length as m-dash]CPh}₄](PF₆), <b>4e</b>; and [Cu₁₂(μ₁₂-Cl)(μ₃-Cl){S₂CN ^<i>n</i> Bu₂}₆{C[triple bond, length as m-dash]CCO₂Me}₃]⁺ <b>5a</b>. Cluster <b>1a</b> is the first structurally characterized copper cluster having a Cu₁₃ centered cuboctahedral arrangement, a miniature of the bulk copper <i>fcc</i> structure. Furthermore, the partial Cu(0) character in the 2-electron superatoms <b>1</b> was confirmed by XANES. Inverse coordination clusters <b>2-5</b> 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 <b>1</b> can be replaced by chalcogen/halogen atoms, resulting in the formation of clusters <b>2-5</b> 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, ¹H, ¹³C NMR, IR, UV-visible, emission spectroscopy, and the structures <b>2a-b</b>, <b>3d-e</b>, <b>4e</b> and <b>5a</b> were established by X-ray diffraction analysis.