F-Block elements prefer trans donor ligands

Abstract

In square planar or octahedral inorganic complexes, strong electron donor ligands typically prefer to bind in a cis rather than trans orientation relative to each other. But chemists have observed the opposite in a few actinide complexes in which strong donor ligands prefer a trans orientation and seem to reinforce each other. A new study suggests that situation may be more common than realized (Nat. Commun. 2017, DOI: 10.1038/ncomms14137). Previously, researchers had observed trans orientations only in linear, high-valent actinyl complexes with hard ligands, such as UO2 2+. In the new work, a team led by Stephen T. Liddle of the University of Manchester and Andrew Kerridge of Lancaster University synthesized cerium(IV), uranium(IV), and thorium(IV) bis(carbene) complexes with linear C=M=C cores and surprisingly short C=M bonds. The effect likely occurs because lanthanide 5p and actinide 6p orbitals can transfer electrons to the 4f and 5f orbitals, respectively, creating electron holes