Isolation of four new Co-II/Co-III and Ni-II complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new Co-II/Co-III and Ni-II complexes with a pentadentate Schiff base ligand H3L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1:2 molar ratio. The room temperature syntheses involving Co-II and Ni-II nitrates and the ligand H3L lead to the isolation of the dinuclear species [Co2L2(H2O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [(Co2Co2L2)-Co-II-L-III(mu(3)-OMe)(2)(NO3)(H2O)(2)]NO3 center dot 2(H2O)(2), and [Ni4L2(mu(3)-OMe)(2)(H2O)(2)]center dot 2H(2)O (4). 1 is found to be a simple mono alkoxo-bridged Co-III dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and mu(3)-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered Co-II and Co-III ions and 4 has both six-and five-coordinate Ni-II centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, H-1-NMR and ESI mass study results and is supposed to have one Ni-II center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.