Hydride Induced Formation and Optical Properties of Tetrahedral [Cu 4 ( μ 4 -H)( μ 2 -X) 2 (PPh 2 Py) 4 ] + Clusters (X = Cl, Br; Py = pyridyl)

Three standalone tetrahedral copper hydride clusters, [Cu4(μ4-H)(μ2-X)2(PPh2Py)4]+ (X = Cl, Br; Py = pyridyl), containing a tetrahedral [Cu4(μ4-H)] unit have been synthesized and structurally characterized. The six Cu–Cu distances of the [Cu4(μ4-H)] unit can be divided into three groups (2.65, 2.85, and 2.95 A), lowering the idealized point group of the Cu4 core to D2 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 A) 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 Cu4 cavity adopts the superatomic electronic configuration of 1S2.