Hydride Induced Formation and Optical Properties of Tetrahedral [Cu4(μ4-H)(μ2-X)2(PPh2Py)4]+ Clusters (X = Cl, Br; Py = pyridyl)

Three standalone tetrahedral copper hydride clusters, [Cu-4(mu(4)-H)(mu(2)-X)(2)(PPh2Py)(4)](+) (X = Cl, Br; Py = pyridyl), containing a tetrahedral [Cu-4(mu(4)-H)] unit have been synthesized and structurally characterized. The six Cu-Cu distances of the [Cu-4(mu(4)-H)] unit can be divided into three groups (2.65, 2.85, and 2.95 angstrom), lowering the idealized point group of the Cu-4 core to D-2 symmetry, thereby resulting in intrinsically chiral metal clusters which exist as racemic pairs of enantiomers in the centrosymmetric crystal structures. Strong photoluminescence (attributable to the existence of the two short Cu-Cu distances of 2.65 angstrom) was observed in solution and in the solid state upon near-UV irradiation. According to the Jellium model, the title clusters can be considered as two-shell Jelliumatic systems with superatomic electron counts of 2e@0e corresponding to the two shells of H-@[Cu4X2(PPh2Py)(4)](2)(+). The four-coordinated hydride in the tetrahedral Cu-4 cavity adopts the superatomic electronic configuration of 1S(2).