Synthesis, Structure, Magnetic Properties, and ¹H NMR Studies of a Moderately Antiferromagnetically Coupled Binuclear Copper(II) Complex

Abstract

A binuclear Cu(II) complex of [(Cu(2)(HAP)(2)IPA)(OH)(H(2)O)](ClO(4))(2).H(2)O (HAP = 3-amino-1-propanol; IPA = 2-hydroxy-5-methylisophthalaldehyde) has been synthesized and characterized by X-ray crystallography, by solid state magnetic susceptibility, and in solution by (1)H NMR studies. The binuclear copper(II) complex crystallizes in the orthorhombic system, space group Pbcn, a = 27.9972(9) Å, b = 8.8713(3) Å, c = 19.5939(6) Å, and Z = 8. The two copper(II) atoms in this binuclear Cu(II) complex are bridged by the oxygen atoms of the phenolate and hydroxy groups. The axial position at one Cu atom is occupied by a water molecule while another Cu has weak interaction with a perchlorate group. The coordination geometries around the two Cu atoms are distorted square pyramid and square planar. The solid state magnetic susceptibility measurement reveals a moderate antiferromagnetic exchange interaction between the two Cu atoms with a -2J value of 113 +/- 9 cm(-)(1). The variable-temperature (1)H NMR studies in CD(3)CN solution show that the observed relatively sharp hyperfine shifted signals follow a Curie behavior. The exchange coupling constant (-2J) obtained in solution by using chemical shift as a function of temperature also reveals a moderate antiferromagnetic exchange interaction between two Cu(II) ions. An analysis of the relaxation data shows that the reorientational correlation time (tau(c)) is dominated probably by a combination of electronic relaxation time tau(s) and rotational correlation time (tau(r)) due to an exchange-modulated dipolar mechanism for this moderately antiferromagnetically coupled binuclear copper(II) system.

Synthesis and antioxidant activities of Schiff bases and their complexes: a review

“…In addition, some complexes, for example di( o ‐hydroxyacetophenone)ethylenediimine–Co. (II), do not show any affinity for dioxygen …”

“…(II) and rac ‐ and meso ‐butane‐2,3‐diylbis(salicylideneiminato)–Co. (II), that have an irreversible dioxygen coordination . In addition, some complexes, for example di( o ‐hydroxyacetophenone)ethylenediimine–Co.…”

“…[22] The electron density-donating substituents, such as alkyl, alkoxy and halides, increase the coordination rate, whereas substituents withdrawing electron density, such as alkyl, carboxylic and nitro groups, decrease it because they induce a lower charge density of the central ion which in turn results in more difficult oxidation of the ion. [23][24][25] However, Co. salen-type complexes with tert-butyl groups in the salicylidene moieties have been reported to have a good affinity for dioxygen when the cyclohexyl bridge between the imine moieties is functionalized with OH groups hydrogen bonded to the coordination dioxygen. [26] The dioxygen coordination can occur via different modes, the preferred mode in each particular case depending on the ligand, and the species present in solution if the complexes are studied in solution.…”

“…2) activate dioxygen reversibly, there are still complexes, for instance (bis(salicylaldehyde)methylene-p,p'-diphenylenediaminato)-Co.(II), (di(salicylal)-3,3-diimino-di-n-propylamine)-Co.(II) and rac-and meso-butane-2,3-diylbis(salicylideneiminato)-Co.(II), that have an irreversible dioxygen coordination. [24] In addition, some complexes, for example di(o-hydroxyacetophenone)ethylenediimine-Co.(II), do not show any affinity for dioxygen. [24] Cedeno et al have reported the catalytic oxidation of models of guaiacyl (G) and syringyl (S) subunits in lignin to their corresponding p-quinones in the presence of molecular oxygen.…”

“…[24] In addition, some complexes, for example di(o-hydroxyacetophenone)ethylenediimine-Co.(II), do not show any affinity for dioxygen. [24] Cedeno et al have reported the catalytic oxidation of models of guaiacyl (G) and syringyl (S) subunits in lignin to their corresponding p-quinones in the presence of molecular oxygen. The oxidation of syringyl-like phenols readily occurred with five-coordinate cobalt catalysts in which one of the ligands is a monodentate pyridine or imidazole base that coordinates axially to the metal.…”