EPR spectra and structures of dinuclear copper(II) complexes with acyldihydrazones of benzenedicarboxylic acids

Abstract

Spacer armed dinuclear copper(II) complexes with condensation products of isophthalic and terephthalic acid dihydrazides with salicylaldehyde and 2 hydroxyacetophenone were synthesized and studied by EPR and X ray diffraction. The compositions and structures of most of the complexes were determined by elemental analysis, thermogravimetric analysis, and IR spectroscopy. The structure of the copper(II) complex with acyldihydrazone of salicylalde hyde and 1,3 benzenedicarboxylic acid (H 4 L) with the composition [Cu 2 L 1 •2morph•MeOH] (morph is morpholine) was established by X ray diffraction. The Cu II atoms are spaced by 10.29 Å and are structurally nonequivalent. One copper cation has a square planar coordi nation formed by donor atoms (2 N + O) of the doubly deprotonated acylhydrazine fragment and the N atom of the morpholine molecule. The second copper atom is additionally coordi nated by a methanol molecule through the oxygen atom, so that this copper atom is in a tetragonal pyramidal coordination with the oxygen atom in the axial position. The EPR spec tra of liquid solutions of the complexes based on 1,4 benzenedicarboxylic acid acyldihydrazones and 1,3 benzenedicarboxylic acid bis(salicylidene)hydrazone at room temperature show a four line hyperfine structure with the constant a Cu = 54.4-67.0•10 -4 cm -1 (g = 2.105-2.147), which is indicative of the independent behavior of the paramagnetic centers. The EPR spec trum of a solution of the complex based on isophthalic acid and 2 hydroxyacetophenone shows the seven line hyperfine structure corresponding to two equivalent copper nuclei (g = 2.11, a Cu = 36.5•10 -4 cm -1 ).The electron delocalization determines the electron density distribution in the molecule, which is responsible for the reactivity of these compounds, the character of metal-ligand bonds in d metal coordination compounds with chelate ligands, the magnetic properties in the pres ence of unpaired electrons, etc. Earlier, it has been com monly accepted that the electron delocalization occurs only in the conjugated π system and cannot occur over σ bonds because the latter are orthogonal to each other (overlap integral is equal to zero). However, there is ex perimental evidence that the spin density of the unpaired electron of the central metal atom is located on atoms of chelate ligands coordinated to the metal atom by several σ bonds.Earlier, it has been demonstrated 1,2 that the electron delocalization in d metal chelate complexes, as opposed to organic compounds, can occur both in the conjugated π bond system and in the σ bond chain.We have studied 1,3 dinuclear copper(II) complexes, in which two mononuclear copper(II) chelate complexes with tridentate bicyclic ligands are linked to each other by -(CH 2 ) n polymethylene bridges (spacers) L is pyridine or piperidine † Deceased.

SN-Donor Methylthioanilines and Copper(II) Complexes: Synthesis, Spectral Properties, and In Vitro Antimicrobial Activity

“…The spectra consist of two g values (g ‖ and g ⊥ ) in the range 2.052-2.293 ( Table 2). These values are typical of copper(II) coordination to electron-donating group (such as nitrogen) [19]. The relation g ‖ > g ⊥ > g o (g o = 2.0023) observed in the EPR spectra of the copper(II) complexes is consistent with an elongated octahedral, square pyramidal or square planar geometry with d x…”