Project information
Understanding the Zero-Field Splitting Parameters of Iridium Pincer Complexes by Means of Quantum Chemistry (Understanding ZFS)

Planar Ir complexes play a crucial role in the catalysis of oxidation-reduction reactions. Electron paramagnetic resonance (EPR) and paramagnetic nuclear magnetic resonance (pNMR) spectroscopies are powerful tools for their characterization. For related octahedral Ru(III) complexes, EPR and pNMR parameters have been explored within the previous research of the applicant [Cidlinská et al. Chem. Sci., under revision]. In case of high-spin Ir counterparts, novel interactions are present which are summarized in the zero-field splitting (ZFS) parameters. ZFS arises from the magnetic dipole spin-spin coupling as well as from the spin-orbit coupling; therefore, any quantum chemical calculation must additionally incorporate relativistic effects.
Recently, two unprecedented Iridium complexes have been synthetised with an electronic triplet ground state: an Iridium(IV) imido complex [Ir(NtBu)(PNP)]+, and an Iridium(III) oxo complex [IrO(PNP)], where PNP=N(CHCHPtBu2)2. Both complexes have a large ligand-centered radical character which makes them attractive to examine electronic effects. The goal of this project is to understand the effect of ligand substitution on the spin state and, potentionally, on the ZFS parameters.
Initial calculations will be performed for the terminal oxo complex with the aim to calibrate the computational methodology on the published theoretical and experimental ZFS parameters. Then, oxygen will be substituted by its heavier chalcogen counterparts. Given that the triplet ground state will be preserved at least for some of the heavier chalcogens, the dependence of the ZFS parameters on the chalcogen will be explored.
In the case that all heavier chalcogens lead to a singlet ground state, the student should focus on the imido complex, and substitute the conformationally flexible t-Bu group by the CH3 group. If the triplet ground state is preserved, nitrogen should be substituted by its heavier pnictogen congeners.
Should all congeners of the oxo/imido complexes be diamagnetic, the focus will be put on the reasons for the low-spin configuration preference. Frontiar molecular orbital analysis should be performed and interpreted in terms of orbital interactions. Accordingly, factors preferring low- and high-spin configuration should be pinpointed for Ir pincer complexes and tested by high-level ab initio calculations.