Density Functional Calculations for Prediction of 57Fe Mossbauer Isomer Shifts and Quadrupole Splittings in β-Diketiminate Complexes

The relative ease of Mossbauer spectroscopy and of density functional theory (DFT) calculations encourages the use of Mossbauer parameters as a validation method for calculations, and the use of calculations as a double check on crystallographic structures. A number of studies have proposed correlations between the computationally determined electron density at the iron nucleus and the observed isomer shift, but deviations from these correlations in low-valent iron beta-diketiminate complexes encouraged us to determine a new correlation for these compounds. The use of B3LYP/def2-TZVP in the ORCA platform provides an excellent balance of accuracy and speed. We provide here not only this new correlation and a clear guide to its use but also a systematic analysis of the limitations of this approach. We also highlight the impact of crystallographic inaccuracies, DFT model truncation, and spin states, with intent to assist experimentalists to use Mossbauer spectroscopy and calculations together.