Electronic structure and Mössbauer quadrupole splittings in iron (II) pentacyanides

Multiple-scattering calculations have been performed for the isoelectronic series of the iron (II) pentacyanides Fe${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_5$ ${\mathrm{NO}}^{2-}$, Fe${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_5$ ${\mathrm{CO}}^{3-}$, and Fe${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_5$ ${\mathrm{N}}_2^{3-}$. Fe $3d$ and $4p$ populations and total electron densities at the iron nucleus derived from these calculations are used to interpret experimental Mössbauer quadrupole splittings and electric field gradients at the iron nucleus. Covalency effects involving the Fe $3d$ and $4p$ orbitals ($\pi$ back donation and $\sigma$ donation, respectively) are found to play a major role in the calculated field gradients. The calculated quadrupole splittings are found to be in good agreement with the experimental values.