Facile synthesis of Cu(II) complexes of mono- and bicondensed N donor Schiff base 1H-pyrazolate ligands: Crystal structures, spectroscopic and magnetic properties

Two [2 × 2] grid-like complexes, [Cu4(L1)4]·2МеОН·2Н2О·dmf (1) and [Cu4(L2)4]·2NaClO4·2МеОН (2) based on new substituted pyrazole ligands 5-(1-((2-aminoethyl)imino)ethyl)-4-methyl-1H-pyrazole-3-carboxylic (H2L1) acid and 5-(1-((3-aminopropyl)imino)ethyl)-4-methyl-1H-pyrazole-3-carboxylic acid (H2L2) have been synthesized and characterized spectroscopically and crystallographically. It was found that the ligand H2L2 condenses with 3-acetyl-4-methyl-pyrazole-5 carbonic acid (H2L) to produce a new dinuclear Cu(II) complex upon reaction with Cu(ClO4)2·6H2O and CuAc2·2H2O. In the grid complexes the four Cu(II) atoms are in square-pyramidal environment formed by two pyrazole, imine and amine N atoms, and the carboxylate O atom and occupy the corners of a [2 × 2] grid with the Cu⋯Cu separations, varying from 3.998(1) to 4.2049(9) and 4.794(1) to 5.091(1) Å for the adjacent and diagonal atoms, respectively. In the dinuclear complex 3 the metal ions are found in square planar environment with their coordination planes lying roughly within the plane of the pyrazolate heterocycle. The separation between Cu(II) centers is 3.921(1) Å. Magnetic susceptibility measurements of 3 revealed the presence of strong antiferromagnetic interaction, with a J value of −207.5 cm−1. This is larger than the J values found for the 1 and 2 grid complexes, which are −20.2 and −18.3 cm−1, respectively.

New Schiff based pyrazole ligands of the zwitterionic type were synthesized. The reactions of copper(II) salts in methanol yielded pyrazolate bridged di- and tetranuclear complexes. Solution behavior, structural features and magnetic properties of the obtained complexes were studied.Figure optionsDownload as PowerPoint slideHighlights
► The reactivity of the zwitterionic pyrazolate ligands were explored.
► Two different types of copper(II) complexes were obtained from the same reactants.
► X-ray and spectroscopic studies of the polynuclear complexes were performed.
► For the studied complexes the antiferromagnetic exchange is mediated by the pyrazolate bridges.