Two new alkoxo-bridged dinuclear copper(II) complexes with 3-aminopyrazidine-2-carboxylic acid as ligands

Abstract

The synthesis, spectroscopic and magnetic properties of two new alkoxo-bridged dinuclear copper(II) complexes are described. Both compounds have the general formula [Cu(μ-OR)(L)2]2X2 · H2O, in which μ-OR = CH3O− or C2H5O−, L = 3-aminopyrazidine-2-carboxylic acid and X = . The title complexes consist of a dinuclear unit with bridging methoxo for [Cu(μ-OCH3)(L)2]2(NO3)2 · H2O (1) and bridging ethoxo for [Cu(μ-OC2H5)(L)2]2(NO3)2 · H2O (2) with two ligands linked to each copper via pyrazidine N atom, providing a square pyramidal CuN2O2 unit. Both compounds have been synthesized in a one-step reaction and characterized by elemental analysis, FTIR, ESR, electronic spectra and by room temperature magnetic moments. The compounds exhibit antiferromagnetic interaction at room temperature. The UV-vis spectra show three absorption bands, attributed to d–d transitions of copper, ligand → metal charge transfer and π → π*; or n → π*; transitions of ligand. The FTIR spectra indicate Cu2O2 ring vibration in 570–450 cm−1 range. Both complexes show a room temperature magnetic moment of about 1.50 B.M. per copper atom. The X-band electron spin resonance (ESR) studies indicate a weak half-field band, characteristic of the Cu(II)–Cu(II) dimer, observed at about 1600 gauss. The observation of this band strongly suggests that the hyperfine structure arises from a spin triplet species. The spectrum of frozen samples in DMF or in DMSO at liquid nitrogen temperature shows a typical Δm = 1 transition.