Cu(II), Ni(II) and Zn(II) mononuclear building blocks based on new polynucleating azomethine ligand : Synthesis and characterization

Five new mononuclear complexes formed by the polynucleating ligand 2-[1-(3,5-dimethyl)pyrazolyl]-2-hydroxyimino-N′-[1-(2-pyridyl)ethylidene]acetohydrazide (HL): [Ni(L)(HL)]ClO4·2CH3OH (1), [Ni(L)2]·CH3OH (2), [Zn(L)(HL)]ClO4·2CH3OH (3), [Zn(L)2]·CH3OH (4) and [Cu(L)2]·CH3OH (5) were synthesized and characterized by elemental analysis, mass-spectrometry, IR-spectroscopy and X-ray analysis. The complexes reveal distorted octahedral N4O2 coordination arrangement formed by both protonated and deprotonated (1, 3) or two deprotonated ligand molecules (2, 4, 5). The presence of non-coordinated oxime and pyrazole groups resulted in the formation of extensive systems of hydrogen bonds in the crystal packing of 1–5. Potentiometric titrations, ESI-MS and spectrophotometric studies of complex formation in MeOH/H2O solutions indicated the presence of mono- and polynuclear complexes with Cu(II), Ni(II) and Zn(II) ions. The solution studies carried out for an excess of Cu(II) over HL ligand (2:1 and 3:2 M ratio) indicated also the formation of polynuclear Cu3L2Hx species, with an involvement of additional nitrogen donors in copper coordination. In binuclear complex [Cu2(L)2(DMF)2](ClO4)2·DMF(6) obtained in solid state, the Cu(II) coordination, analogous to the one in 1–5, was supported by pyrazole N atom.