In this article, we present an improved density functional theory (DFT) strategy for the calculation of isomer shifts \(\:\delta\:\) and quadrupole splittings \(\:\varDelta\:{E}_{Q}\) of iridium complexes. For the iridium(I) complex ([IrCl(COD)]2) we obtain \(\:\delta\:\) = -0.63 mms-1 and \(\:\varDelta\:{E}_{Q}\) = 3.81 mms-1. Our calculation reproduce the negative sign determined experimentally by Gál et al. (Journal of Radioanalytical and Nuclear Chemistry 260 (2004) pp. 133–142). The calculations also reproduce the values of \(\:\delta\:\) and \(\:\varDelta\:{E}_{Q}\) in a reasonable manner. We also present calculations of the fullerene adduct C60([IrCl(COD)]2)2 which we consider as a well-defined model system for the exploration of molecule-substrate interaction. The binding of the complex to fullerene leads to an electronic ground state with clearly different Mössbauer parameters: We have calculated \(\:\delta\:\) = -0.90 mms-1 and \(\:\varDelta\:{E}_{Q}\) = -6.06 mms-1, again in good agreement with experimental values reported by Tuczek et al. (Tuczek et al. Fullerene Science and Technology 5 (1997) pp.443–452).
