[Pt@Pb₁₂]^2- A challenging system for relativistic density functional theory calculations of ¹⁹⁵Pt and ²⁰⁷Pb NMR parameters

We report computations of NMR chemical shifts and indirect spin-spin coupling constants (J couplings) for the [Pt@Pb₁₂]^2- "superatom". The system is strongly influenced by relativistic effects. The Pt-Pb coupling constant is predicted to be negative, with its magnitude being in reasonable agreement with experiment. Pt and Pb chemical shifts also agree reasonably well with experiment. The Pb shielding tensor is strongly anisotropic, with a large deshielding principal component dominated by magnetic coupling between frontier orbitals of the cluster that resemble atomic g orbitals. The NMR parameters are sensitive to approximations made in the computations and require the inclusion of spin-orbit coupling in the theoretical model to achieve reliable results. Computing the NMR parameters of the compact [Pt@Pb₁₂]^2- system with its many electrons proves to be a challenging test case for relativistic density functional methods.