Abstract
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 X‐ray 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 [(az)Pt(μ‐Cl)~2~Pt(az)] (4) shows reduction processes which are reversible for 1 and 2 but irreversible for 3 and 4. The first reduction of 1 and 2 leads to radical complexes, and EPR spectroscopy shows the spin to be predominantly located on the azo part of the complexes. The radical complex 2^·–^ shows an unprecedented ^195^Pt hyperfine coupling constant and g anisotropy for such Pt^II^ radical species. The UV/Vis spectroscopy results for all the complexes are also discussed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)