Metal-ligand bonding in copper(II) chelates. Electron paramagnetic resonance study

Abstract

Epr spectra of some cupric /3-ketoenolates, -dioximates, 0-dioximates, and Schiff bases in chloroform solution were recorded at room temperature and at -160°( frozen state). The bonding parameters were calculated from spectral data. The bonding properties of the odd electron were derived as a function of the nature of the ligand donor atoms, the size of the chelate ring, and substituent effects. The relationship between covalency of bonding and complex stability is discussed.This work was aimed at studying the electron spin resonance spectra of several copper(II) complexes and to draw some conclusions concerning the bonding properties of the odd electron, depending on the nature of the donor atoms in the ligands, the size of the chelate ring, and effects of substituents on the chelate ring. The epr spectra of copper(II)-acetylacetonate type complexes have been treated by several authors. [1][2][3][4][5][6] In all of the above complexes, it was assumed that the Cu11 ion is surrounded by the four donor atoms in a planar configuration (Dih symmetry) and that each donor atom has a 2s,2px,2py,2pz atomic orbital available for the formation of molecular orbitals with the atomic d orbitals of the central ion. From group theory, Gersmann and Swalen8 obtained the proper linear combinations of ligand orbitals with the copper d orbitals which form the antibonding wave functions of the planar cupric chelate compound. The expressions for the in-plane antibonding wave functions are Big = Qtdxy --[-(1) + (2> + ffxy(3) -VXy(4) ] Ag = /?dx2_y2 -y2(l -/32)1/2[-pxy(1) -pxy(2) + Pxy<3) + Pxy(4) ] The above wave functions are applicable also for tetradentate Schiff base chelates of C2" symmetry, where the corresponding symmetry designations are B2 and Ai, in the sense used by Swett and Dudek.6

Endohedral Copper(II)acetylacetonate/Single-Walled Carbon Nanotube Hybrids Characterized by Electron Paramagnetic Resonance

“…The compound Cu(acac) 2 (Cu(II), d 9 configuration, I = 3/2) has been quite extensively studied by EPR. − It is a planar molecule with D 2 h symmetry, for which the unpaired electron resides in the d xy orbital. The magnetic axes are conventionally defined such that g z is perpendicular to the molecular plane, g x bisects O−Cu−O angles toward the chelate rings, and g y is perpendicular to that and points between the two chelate rings (see inset of Figure ).…”

“…Although in the literature Cu(acac) 2 EPR spectra are mostly described using axial g - and hyperfine tensors, ,,, better results can be obtained using rhombic tensors, corresponding to the D 2 h molecular symmetry. Furthermore, for the simulation of the EPR spectra of copper complexes, it is also necessary to include two different Cu isotopes [ 63 Cu ( g n = 1.484) and 65 Cu ( g n = 1.588)], taking into account their relative natural abundances (69.2 and 30.8%, respectively).…”

“…Assuming the observed EPR spectrum to originate from encapsulated molecules (which we will show further on), it is clear that, during "thorough" washing, applying an ultrasonic treatment, also a part of the molecules which were initially encapsulated are being removed. Although in the literature Cu(acac) 2 EPR spectra are mostly described using axial g-and hyperfine tensors, 26,27,29,32 better results can be obtained using rhombic tensors, corresponding to the D 2h molecular symmetry. Furthermore, for the simulation of the EPR spectra of copper complexes, it is also necessary to include two different Cu isotopes [ 63 Cu (g n ) 1.484) and 65 Cu (g n ) 1.588)], taking into account their relative natural abundances (69.2 and 30.8%, respectively).…”

Isatin‐Schiff base copper(II) complexes—A DFT study of the metal‐ligand bonding situation

“…Since the complexes 1-12 are paramagnetic and the experimental [10,28] are available for complexes 4-6 and 10-12, the EPR parameters, g and corresponding hyperfine tensors, were evaluated theoretically by employing different density functionals such BP86, BPW91-35, and BPW91-60 [12,17].…”