Synthesis, structure, magnetic properties and aqueous solution characterization of p-hydroquinone and phenol iminodiacetate copper(ii) complexes

Abstract

The reaction of Cu2+ acetate monohydrate with 2-[N,N'-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H4cacp), 2-[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H4cah) and the dinucleating 2,5-bis[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H6bicah) in water results in the formation of several Cu2+ species, which are in dynamic equilibrium in aqueous solution and their stability is pH dependent. A systematic crystallographic study of these species was pursued, resulting in the characterization of most of the species. Additional techniques were employed to characterize the molecules in the solid state (infrared spectroscopy) and in solution (UV-vis spectroscopy and electrochemistry). These measurements show that the Cu2+ ions are ligated mainly to the iminodiacetate at pH < 6, exhibiting only weak interactions with the phenol oxygen. At pH > 6, the phenol oxygen was deprotonated and dinuclear-bridged species, from the phenolate oxygen complexes exhibiting a Cu2+ 2O2 core, were isolated. The coordination environment around the copper ions varies between trigonal bipyramidal, tetragonal pyramidal and distorted octahedral geometries. The two unpaired electrons of the Cu2+ ions are found to be antiferromagnetically coupled. A survey of the magnetic and structural properties of the dinuclear phenoxide bridged Cu2+ complexes shows that the strength of the antiferromagnetic coupling is linearly dependent on the Cu-Ophenolate bond lengths, at bond distances below 1.98 angstroms. The effect of the Cu-O-Cu angles on the magnetic properties of the complexes is also discussed.

In-situ improved phenol adsorption at ions-enrichment interface of porous adsorbent for simultaneous removal of copper ions and phenol

“…The binding energy of the copper in mixed solution adsorption was shifted to 933.8 eV (Fig. 7b), which might indicate Cu 2+ that had been absorbed in carboxylic functionalized PGMA porous monolith formed CAOACu complex, in which oxygen atoms donated electrons to copper and the electron density of copper had increased [45]. It could be deduced that Cu 2+ had been absorbed firstly in carboxylic functionalized PGMA porous monolith, and then the interface enrichment of surplus positive charged had strongly attractive force with the deprotonation of the phenolic oxygen to form CuAO phenolate bond to make up the weaken effect of hydrogen bonding on phenol adsorption.…”

The crystal structure of diaqua-(N-(2-hydroxy-5-nitrobenzyl)iminodiacetato-κ4-N,O,O′,O′′)chromium(III) based on synchrotron data, C11H13CrN2O9

“…They provide a convenient mononucleating feature with the phenolate oxygen and the RN(CH 2 COOH) 2 arm, and have been used to incorporate various mono-or dinuclear cores [4,5]. Recently, we synthetized the ligand NO 2 -H 3 XDA [N-(2-hydroxy-5-nitrobenzyl)iminodiacetic acid], and obtained the title pincer complex.…”

&#963;-Bonded p-Dioxolene Transition Metal Complexes

“…In general, larger substitutions with groups that can form more chelate rings favor the monodentate coordination mode I and smaller groups tend to form binuclear M - The speciation of water soluble complexes is controlled by pH and thus, various structural different complexes can be isolated. (Stylianou, et al, 2008) An example of the structures of the iminodiacetate monosubstituted hydroquinones isolated at different pHs are shown in figure 7. Fig.…”

“…Drawings of the structures of complexes 60 and 55 isolated from acidic and alkaline pHs respectively. (Stylianou, et al, 2008;Zhang, et al, 2009) The numbering of complexes is according to table 1 The Cu II 2 O 2 phenolate is a rare example of an asymmetric bridging core containing two copper atoms, one having a square pyramidal and the other an octahedral coordination sphere. This is the second example reported in the literature of the asymmetric Cu II 2 O 2 phenolate bridged complexes with the two copper ions exhibiting different coordination geometry (octahedral and square pyramidal).…”

“…Although the crystal structures of many of these enzymes have been solved, the role of the metal ions in these reactions is still controversial. From another point of view, quinonoid metal complexes exhibit rich redox, magnetic and photochemical properties and thus can underpin key technological advances in the areas of energy storage, sensors, catalysis and "smart materials" (Evangelio & Ruiz-Molina, 2005;Stylianou, et al, 2008). Metal ions interact with hydroquinone systems, through σ-bonding to the oxygen atoms and/or through π-bonding to the carbocyclic ring.…”