Anion effect on the coordination behavior of N,O-hybrid pyrazole ligand towards Pd(II): synthesis, characterization, and supramolecular properties

Four new Pd(II) coordination complexes using 2-(3-methyl-5-phenyl-1H-pyrazol-1-yl)ethanol (L) with different counter-anions have been prepared to examine their effect on the coordination mode of the ligand as well as on the self-assembly of the supramolecular structure. Reaction of trans-[PdCl2(L)(2)] (R) with AgCF3SO3 gives the ionic complex [Pd(L)(2)](CF3SO3)(2) (1). When AgNO3 is used, [Pd(NO3)(L)(2)](NO3) (2) and [Pd(L)(2)](NO3)(2) (3) are obtained in the ratio 70:30, respectively, where the nitrate ion is present in- and/or outside the coordination sphere. Reaction of R with Ag2SO4 in the presence of (NH4)(2)C2O4 yields [Pd(C2O4)(L)(2)] (4). These new complexes have been characterized by elemental analyzes, conductivity measurements, mass spectrometry, IR, H-1 and C-13{H-1} NMR spectroscopies, and X-ray diffraction, whenever possible. The denticity varies from N-monodentate to NO-bidentate, depending on the conditions, showing the versatility of L. Finally, the results of X-ray diffraction analyzes of 1 reveal that CF3SO3- plays a fundamental role in self-assembly, generating a 2-D supramolecular layer with different inter- and intra-molecular interactions. The easy preparation and the high efficiency of this ligand make it a promising alternative to improve established systems.