Geometrical and electronic structures of dinuclear complex ions {(mu-bpym)[Cu(EAr3)2]2}2+ with intramolecular "organic sandwich" formation (E = P or As; Ar = Aryl; bpym = 2,2'-bipyrimidine).

The compound {(mu-bpym)[Cu(AsPh3)2]2}(BF4)2 (1) has been prepared and studied in comparison with the triphenylphosphine analogue 2. Qualitatively, the structure of 1 with characteristically distorted copper(I) coordination caused by Ph/bpym/Ph sandwich interactions is similar to that of 2 and is approximately reproduced by DFT calculations for the model complex ions {(mu-bpym)[Cu(EMe2Ph)2]2}2+, E = P or As. In contrast, the dinuclear {(mu-bpym)[Cu(P(3-Me-C6H4)3)2]2}(BF4)2 (3) displays a distinctly less distorted metal coordination geometry due to the steric requirements of the methyl groups in the meta-tolyl substituents. The electrochemical reduction of 1 is less reversible than for the phosphine analogues; the one-electron-reduced form 1*- exhibits a broad, unresolved EPR signal at g = 2.0023. Resonance Raman spectroscopy of 1 shows the typical vibrations of the bpym ligand in agreement with the MLCT assignment of the long-wavelength transitions below 500 nm. All three dinuclear complexes exhibit luminescence at room temperature in the solid and in solution.