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Reversibly Reducible cis-Dichloroplatinum(II) and cis-Dichloropalladium(II) Complexes of Bis(1-methylimidazol-2-yl)glyoxal

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posted on 09.07.2007, 00:00 by Ece Bulak, Markus Leboschka, Brigitte Schwederski, Orkan Sarper, Tereza Varnali, Jan Fiedler, Falk Lissner, Thomas Schleid, Wolfgang Kaim
Complexes cis-MCl2(big), big = bis(1-methylimidazol-2-yl)glyoxal, M = Pt, Pd, were prepared and characterized through electrochemistry, spectroscopy, and for M = Pt, by X-ray structure analysis. The seven-membered chelate ring formed through N,N‘ coordination of the ligand big shows a boat conformation in agreement with density functional theory (DFT) calculation results. No significant intermolecular interactions were observed for the platinum compound. Both the PdII and PtII complexes undergo reversible one-electron reduction in CH2Cl2/ 0.1 M Bu4NPF6; the reduced palladium compound disintegrates above −30 °C. Electron paramagnetic resonance (EPR), UV−vis, and IR spectroelectrochemistry studies were employed to study the monoanions. The anion radical complex [cis-PtCl2(big)]•- exhibits a well-resolved EPR spectrum with small but well-detectable g anisotropy and an isotropic 195Pt hyperfine coupling of 12.2 G. DFT calculations confirm the spin concentration in the α-semidione part of the radical complex with small delocalization to the bis(imidazolyl)metal section. The results show that EPR and electroactive moieties can be linked to the cis-dichloroplatinum(II) group via imidazole coordination.