Structures, Redox and Spectroscopic Properties of PdII and PtII Complexes Containing an Azo Functionality

The complexes [PdCl2(pap)] (1) and [PtC](2)(pap)] (2; pap = 2-phenylazopyridine) were synthesized by treating PdCl2 or K(2)ptCl(4), respectively, with pap and characterized by H-1 NMR spectroscopy and elemental analysis. Both these complexes, together with the previously reported complex [(az)Pd(mu-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 [(az)Pt(mu-Cl)(2)Pt(az)] (4) shows reduction processes which are reversible for I and 2 but irreversible for 3 and 4. The first reduction of I 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 Pt-195 hyperfine coupling constant and g anisotropy for such Pt-II radical species, The UV/Vis spectroscopy results for all the complexes are also discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)