Covalent Bonding and the Trans Influence in Lanthanide Compounds

A pair of mer-octahedral lanthanide chalcogenolate coordination complexes [(THF)3Ln(EC6F5)3 (Ln = Er, E = Se; Ln = Yb, E = S)] have been isolated and structurally characterized. Both compounds show geometry-dependent bond lengths, with the Ln−E bonds trans to the neutral donor tetrahydrofuran (THF) significantly shorter than the Ln−E bonds that are trans to negatively charged EC6F5 ligands. Density functional theory calculations indicate that the structural trans influence evidenced by the differences in these bond lengths results from a covalent Ln−E interaction involving ligand p and Ln 5d orbitals.