Correlation of isomer shift and quadrupole splitting and the sign of EFG

Mössbauer isomer shift // and quadrupole splitting /E_Q/ values in a series of isostructural compounds correlate well to give linear relationship provided the sign of electric field gradient /EFG/ is assigned to the E_Q. The correlation has been used in predicting the sign of EFG for some monosubstituted pentacyanoferrate/II/ complexes. Usefulness of such correlations and its limitations are presented.