Investigations of the EPR parameters for the tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br)

TL;DR

This paper theoretically investigates EPR parameters of tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br), emphasizing charge transfer effects and their dependence on covalency and spin-orbit coupling.

Contribution

It introduces a comprehensive model considering both crystal-field and charge transfer contributions to EPR parameters for these clusters.

Findings

Charge transfer significantly influences g-shift, especially with increased covalency.

Charge transfer contribution is larger in AgBr than in AgCl.

Unpaired spin densities are quantitatively determined from molecular orbital coefficients.

Abstract

The EPR parameters g factors and the superhyperfine parameters for the tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a 3d^5 ion under tetrahedra by considering both the crystal-field and charge transfer contributions. The related model parameters are quantitatively determined from the cluster approach in a uniform way. The g-shift \Delta g (=g-g_s, where g_s\approx 2.0023 is the spin only value) from the charge transfer contribution is opposite (positive) in sign and much larger in magnitude as compared with that from the crystal-field one. The importance of the charge transfer contribution increases rapidly with increasing the covalency and the spin-orbit coupling coefficient of the ligand and thus exhibits the order of AgCl<AgBr. The unpaired spin densities of the halogen ns, np\sigma\ and np\pi\ orbitals are quantitatively determined from the related molecular orbital coefficients based on the cluster approach.