η<sup>6</sup>-Benzene Tetra-Anion Complexes of Early and Late Rare-Earth Metals
Ming Liu, Yan‐Cong Chen, Arpan Mondal, Huan Wang, Ming‐Liang Tong, Richard A. Layfield, Fu‐Sheng Guo
Abstract
High Resolution Image Download MS PowerPoint Slide A novel synthetic route to the triple-decker benzene tetra-anion complexes [(η 5 -C 5 i Pr 5 )M(μ:η 6:η 6 -C 6 H 6 )M(η 5 -C 5 i Pr 5 )] is reported for a range of early and late rare-earth elements, i.e., M = Y, La, Sm, Gd, and Dy ( 1 M ). The lanthanum complex 1 La is the first benzene tetra-anion complex of the largest rare-earth element. Aromaticity in the 10π-electron benzene ligands is confirmed through crystallographic studies of all compounds and nucleus-independent chemical shift calculations on 1 Y and 1 La . Analysis of the bonding in 1 Y and 1 La using density functional theory revealed strong covalency in the metal-benzene interactions, with very similar contributions from the metal 4d/5d orbitals, respectively, and the benzene π* orbitals. Magnetic susceptibility measurements on 1 Sm, 1 Gd, and 1 Dy are also consistent with the presence of a benzene tetra-anion ligand. The origins of the appreciable exchange coupling constant of J exch = −3.35 cm –1 (−2 J formalism) in 1 Gd are established through a computational study of the interacting magnetic orbitals. The dynamic magnetic properties of 1 Dy are also described. The clear absence of SMM behavior in the dysprosium complex is explained using multireference calculations and an ab initio ligand-field theory description of the 4f orbitals, which clearly show that the benzene tetra-anion ligand provides a dominant equatorial contribution.