Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff baseligand: syntheses, structural descriptions and magnetic studies

Abstract

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, [Co^II₂Co^III₂L₂(μ₃-OMe)₂(NO₃)(H₂O)₂]NO₃·2(H₂O) (2), and [Ni₄L₂(μ₃-OMe)₂(H₂O)₂]·2H₂O (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 μ₃-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, ¹H-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.