Understanding the Multiconfigurational Ground and Excited States in Lanthanide Tetrakis Bipyridine Complexes from Experimental and CASSCF Computational Studies

Robert Halbach (1) , Grégory Nocton (2, 1) , Jorge Amaro-Estrada (3) , Laurent Maron (3) , Corwin A Booth (4) , Richard A Andersen (1, 4)

1 Department of Chemistry [Berkeley]
2 LCM - Laboratoire de chimie moléculaire
3 LPCNO - Laboratoire de physique et chimie des nano-objets
4 CSD - Chemical Sciences Division [LBNL Berkeley]

An alternative synthesis for M(κ2-bipy)4 (M = La, Ce) and [Li(thf)4][M(κ2-bipy)4] (M = Tb, Dy) and the crystal structures for M = La, Ce, and Tb are described. The isomorphous and isostructural neutral molecules, M = La and Ce, are polymeric in the solid-state, as are those of M = Sm and Eu, which were reported in earlier work. The polymeric network is built from eight coordinate units whose geometry in all four cases is that of a square prism. The known molecules, M = Yb and Lu, are also polymeric, but the eight coordinate units have dodecahedral geometries. The structure of the anions in the separated ion pair, [Li(thf)4][M(κ2-bipy)4], in which Tb is reported in this work and Lu is known, are monomeric with geometries that are between that of a square antiprism and a dodecahdron. The electronic structure, from CASSCF multireference quantum mechanical calculations, shows that the electronic ground states for M = La and Lu are multiconfigurational spin doublets and those for the M = Ce and Yb are multiconfigurational spin triplets. This is confirmed by magnetic susceptibility studies as a function of temperature that are consistent with the metals (La, Ce, Sm, Tb, Dy, Yb, and Lu) being trivalent, as are the LIII-edge XANES spectra (Ce, Yb), and divalent for Eu. The multiconfigurational nature of the ground states, developed from CASSCF molecular orbital calculations, renders a single Lewis structure and a single reference molecular orbital representation misleading. The results from the multireference calculations are extended to the other lanthanide molecules and are the genesis of a new model for understanding the magnetic properties of these molecules.

Domaines: Chimie inorganique

Robert Halbach, Grégory Nocton, Jorge Amaro-Estrada, Laurent Maron, Corwin A Booth, et al.. Understanding the Multiconfigurational Ground and Excited States in Lanthanide Tetrakis Bipyridine Complexes from Experimental and CASSCF Computational Studies. Inorganic Chemistry, 2019, 58 (18), pp.12083-12098. ⟨10.1021/acs.inorgchem.9b01393⟩. ⟨hal-02289195⟩