The heterodinuclear compound [(PhenQ)Cu(dppf)](BF4), PhenQ = 9,10-phenanthrenequinone and dppf = 1,1'-bis(diphenylphosphino)ferrocene, was identified structurally and spectroscopically (NMR, IR, UV-vis) as a copper(I) complex of a completely unreduced ortho-quinone. Crystallographic and DFT calculation results suggest that this stabilization of a hitherto elusive arrangement is partially owed to intramolecular pi/pi interactions phenyl/PhenQ. Intermolecular PhenQ/PhenQ pi stacking is also observed in the crystal. According to DFT calculations, the pi interactions are responsible for the considerably distorted coordination geometry at CuI with one short and one longer Cu-O and Cu-P bond, respectively, and with bond angles at copper ranging from 99 degrees to 133 degrees. Electrochemical reduction proceeds reversibly at low temperatures to yield an EPR spectroscopically characterized semiquinone-copper(I) species.

The complexes [PdCl 2 (pap)] (1) and [PtCl 2 (pap)] (2; pap = 2-phenylazopyridine) were synthesized by treating PdCl 2 or K 2 PtCl 4 , respectively, with pap and characterized by 1 H NMR spectroscopy and elemental analysis. Both these complexes, together with the previously reported complex [(az)Pd(µ-Cl) 2 -Pd(az)] (3; az = azobenzene), were also characterized by Xray crystallography. The structures of 1, 2, and 3 show a slightly elongated N-N azo double bond due to back-donation from the metal centers and a twisting of the uncoordinated part of the ligands with respect to the rest of the molecule. Cyclic voltammetry of 1, 2, 3, and the related complex

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