Multiple established forms of palladium acetate binding to the four N-atom donor 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp]

The reaction of the ligand 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp], with Pd(OAc)2, in CH3CN leads to the formation of three novel complexes which were characterized by thermogravimetric analysis, single crystal and powder X-ray measurements, MALDI-TOF mass spectra, IR and UV–visible spectroscopy as well as electrochemistry. As established by crystallographic work, the complex of formula [(CN)2dppPd(OAc)2]⋅H2O (molar ratio ligand/Pd(II) 1:1; species 3) shows a single Pd(OAc)2 unit coordinated to each nitrogen of the two pyridyl (py) groups of [(CN)2dpp]. i.e. the “py-py” mode of coordination previously established for the analogs [(CN)2dppMCl2] (M = Pd(II), Pt(II)). The second isolated species is a highly insoluble dinuclear Pd(II) complex of formula [(CN)2dpp{Pd(OAc)2}2]⋅5H2O (molar ratio ligand/Pd(II) 1:2; species 1), where the two Pd(OAc)2 units are each coordinated to one pyrazine nitrogen and one N atom of a pyridyl group on [(CN)2dpp] (“py-pyz” binding). Based on crystallographic work, the third isolated species is assigned the formula [(CN)(CONH)dppPd(OAc)] (molar ratio ligand/Pd(II) 1:1; species 2), which is formed by hydrolysis of a CN substituent on [(CN)2dpp] giving a –CONH- group and characterized by a “py-pyz” type of coordination. Electrochemical and spectroelectrochemical data of complexes 1, 2, and 3 in DMF and DMSO were used to assign the sites of electron transfer.