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artículo con referato
"Stereoisomers of palladium(II) complexes with the dipyridyl ligands 2,3-di(2-pyridyl)pyrazine (dpp), 2,3-di(2-pyridyl)quinoxaline (dpq) and 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline (ddpq). Crystal structure of [Pd(dpq)2](PF6)2"
J. Granifo, M.T. Garland and R. Baggio
Inorg. Chim. Acta 348 (2003) 263-270
A solid-state and solution study to characterize the possible configurations of the [Pd(L)2]2+ cations (L=dpp, dpq, ddpq) has been carried out. To accomplish this objective the homoleptic complexes [Pd(L)2](hfac)2 (L=dpp, dpq, ddpq; HFAC=hexafluoroacetylacetonate ion) were isolated. The syntheses were performed in diethyl ether by reacting [Pd(hfac)2] with a two molar equivalent of the respective L ligand. Besides, X-ray quality crystals were obtained by metathesis with NH4PF6 to derive the hexafluorophosphate species [Pd(dpq)2](PF6)2. The X-ray crystallographic study shows that the coordination sphere of the [Pd(dpq)2]2+ cation is square planar and that the bidentate chelating dpq ligands are linked via their N-pyridine atoms. Furthermore, the cation structure reveals an intramolecular ππ stacking between the two quinoxaline rings in a “pincer-like” configuration. In CDCl3 solution, the 1H NMR spectra of the [Pd(L)2](hfac)2 complexes permit to infer the presence of a mixture of two isomeric forms with different populations. The results suggest that the predominant form being that of the solid-state “pincer-like”. For the less abundant species a configuration with the quinoxaline groups (dpq, ddpq) or pyrazine groups (dpp) in opposite side respect to the plane of the Pd(II) centre, “step-like”, is suggested. The preponderance of the “pincer-like” configuration was attributed to the influence of the aromatic ππ stacking interactions.
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