The Electron Spin Resonance Spectrum of Copper-Doped Palladium bis-Benzoylacetonate Crystals

Abstract

The EPR spectrum of about 0.5% Cu²⁺ diluted into the two crystalline forms of Pd bis-benzoylacetonate is reported. The spectrum of the ($11\bar{1}$) face of the needle modification shows an anomalous doubling of the EPR lines which is explained by the presence of twinning in this crystallographic form. The principal g values and directions have been obtained in terms of an arbitrary molecular coordinate system using a specially written computer program. The following parameters result: g_x = 2.049₀; g_y = 2.047₈; g_z = 2.242₈; A = −181 x 10⁻⁴ cm⁻¹, B = − 28 x 10⁻⁴ cm ⁻¹; with the in-plane g axes lying approximately between, rather than along, the copper-oxygen bonds. These results are used to estimate bonding parameters for the molecule. For comparative purposes bonding parameters for Cu bis-acetylacetonate have been recalculated from the EPR data of Maki and McGarvey using recent estimates of the d-level energies. While the σ-bonding molecular orbital coefficients are almost the same in the two chelates, both the in-plane and out-of-plane π-bonding coefficients are significantly smaller in the complex with the phenyl-substituted ligand. The orientation of the g tensor implies that the along-the-bonds rhombic effect of the phenyl groups does not affect the orientation of the (xz) and (yz) orbitals, and causes ho significant contamination of the ground-state orbital by the (3z² − r²) orbital, which can therefore be ignored in deriving the covalency parameters.

Supported by the Advanced Research Projects Agency Contract SD-131 through the Materials Research Laboratory at the University of Illinois, and the Illinois Graduate Research Board.