Experimental and DFT/TDDFT Studies on the 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)2Py2Qx], its metallated derivatives [(CN)2Py2QxMCl2] (M = PdII, PtII) and their analogues sharing the dicyanopyrazine fragment are presented and discussed. X-ray work on the new quinoxaline complex [(CN)2Py2QxPtCl2] establishes that PtII 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 PtII 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.