Dissection of bicapped octahedral copper hydride cluster to form two chiral tetrahedral copper hydride cluster series exhibiting auto deracemization and photoluminescence

Abstract

Three series of copper hydride clusters [Cu₈H₆L₆]²⁺ (1), [Cu₄HX₂L₄]⁺ where X⁻ = Cl⁻ (2a), Br⁻ (2b), I⁻ (2c), N₃⁻ (2d) and SCN⁻ (2e), and [Cu₄HX₃L₃] where X⁻ = Br⁻ (3b) and I⁻ (3c) (L = 2-(diphenylphosphino)pyridine, dppy) were synthesized and characterized by single-crystal X-Ray crystallography and standard spectroscopic techniques. The metal core of 1, Cu₈, can be described as a bicapped octahedron, while those of 2 and 3 series adopt tetrahedral structures. The hydride positions were deduced from difference electron density maps and corroborated by NMR and DFT calculations. For 1, there are two μ₄-H⁻, one each in the two tetrahedral cavities of the two capping atoms and four μ₃-H⁻ on the six triangular faces around the waist of the octahedron. For [Cu₄HX₂L₄]⁺ and [Cu₄HX₃L₃] series, the single μ₄-H⁻ resides in the center of the Cu₄ tetrahedron. It was found that these three series of copper clusters are intimately connected and can convert from one to another under specific reaction conditions. Their transformation pathways were investigated in detail. Spontaneous resolution to form optically pure enantiomeric single crystals was observed for [Cu₄H(SCN)₂L₄]⁺ (2e) and [Cu₄HBr₃L₃] (3b). Photoluminescence was observed for [Cu₄HX₂L₄]⁺, as well as [Cu₄HX₃L₃] with strong emissions from green to yellow regions.