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{CCR′}₄](PF₆), 1a–d (where a: R = ⁿBu, R′ = CO₂Me; b: R = ⁿBu, R′ = CO₂Et; c: R = ⁱPr, R′ = CO₂Et; d: R = ⁿPr, R′ = 3,5-(CF₃)₂C₆H₃); [Cu₁₂(μ₁₂-S){S₂CNR₂}₆{CCR′}₄], 2a–c; [Cu₁₂(μ₁₂-Cl){S₂CNR₂}₆{CCR′}₄](PF₆), 3a–e (where e: R = ⁿBu, R′ = Ph); [Cu₁₂(μ₁₂-Br){S₂CNⁿBu₂}₆{CCPh}₄](PF₆), 4e; and [Cu₁₂(μ₁₂-Cl)(μ₃-Cl){S₂CNⁿBu₂}₆{CCCO₂Me}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, ¹H, ¹³C NMR, IR, UV-visible, emission spectroscopy, and the structures 2a–b, 3d–e, 4e and 5a were established by X-ray diffraction analysis.