Experimental and DFT/Time-Dependent DFT Studies on Neutral and One-Electron-Reduced Quinoxaline and Pyrazine Precursors and Their Mononuclear (PdII, PtII) Derivatives

Electrochemical and UV/Vis spectral studies on the quinoxaline compound 2,3-di(2-pyridyl)-6,7-dicyano-1,4-quinoxaline, [(CN)(2)Py(2)Qx], its metallated derivatives [(CN)(2)Py(2)QxMCl(2)] (M = Pd-II, Pt-II) and their analogues sharing the dicyanopyrazine fragment are presented and discussed. X-ray work on the new quinoxaline complex [(CN)(2)Py(2)QxPtCl(2)] establishes that Pt-II is coordinated to the pyridine N atoms (py-py coordination). The spectra of the 1- charged quinoxaline and pyrazine compounds show new intense absorptions in the region of 500-900 nm, and redshifted bands in the 250-400 nm region. By using DFT/time-dependent DFT calculations, the spin density and spectral features of both couples of precursors and Pt-II derivatives were investigated in terms of single-electron excitations between the Kohn-Sham orbitals of the optimized structures in the gas and condensed phases. A detailed comparison is allowed of the experimental and calculated spectral features of the neutral and 1- charged species.