Magnetism of transition-metal-doped tetrel nanoclusters: multi-reference character and spin-orbit effects in Sn12TM (TM = Cr, Mn, Fe).

The magnetic behavior of endohedrally transition-metal-doped tetrel clusters Sn12TM (TM = Cr, Mn, Fe) was investigated using a combined experimental and theoretical approach. Based on an improved experimental setup, the magnetic deflection was measured over a wide temperature range of Tnozzle = 16-240 K. From a Curie analysis of the experimentally observed single-sided shift at high nozzle temperatures, the spin multiplicities and g-factors were determined. It was observed that all three nanoclusters analyzed are paramagnetic, with Sn12Mn being a sextet with g = 2.1 ± 0.1, while Sn12Cr is a quintet with the same g-factor and Sn12Fe is also a quintet but with a higher g-factor of 2.4 ± 0.1. In order to better understand the interplay between geometric and electronic structures and their influence on magnetism, a global geometry optimization was carried out, followed by a quantum-chemical analysis of the electronic structure using density functional theory (DFT) and wavefunction methods. The multi-reference calculations proved particularly important for Sn12Fe because DFT fails to correctly predict the value of the g-factor. To describe the electronic ground state of Sn12Fe, two reference configurations must be taken into account. A charge transfer from the Sn ligands to Fe manifests in very low-lying electronic excitations. These charge transfer excitations lead to a significant increase in the g-factor compared to the value of the free electron due to the large spin-orbit coupling constant of Sn. As a result, in contrast to Sn12Mn and Sn12Cr, the spin density of Sn12Fe is strongly delocalized over the entire cluster framework.