Mössbauer isomer shift calibration of some high spin ionic complexes of iron with halogen ligands through a CNDO MO calculation

The Mössbauer isomer shift calibration constant, α, relating the chemical isomer shift linearly to the net electron density at the corresponding nucleus is evaluated for a few high spin ionic complexes of iron. In the first scheme the net electron density |ψ(0)|2 at the Fe nucleus for the various complexes are evaluated through a pseudo-atom formulation using the interpolation formula of Blomquist et al. involving the corresponding 3d, 4s and 4p populations obtained through a CNDO (open shell) MO calculation. The α thus obtained is improved towards earlier results by considering additional contributions to |ψ(0)|2 due to the nonorthogonality of the Fe core orbitals, namely Fe 3s, with the ligand orbitals and also additional contributions from cross and distant ligand terms