Controlling uranyl oxo group interactions to group 14 elements using polypyrrolic Schiff-base macrocyclic ligands

Abstract

Heterodinuclear uranyl/group 14 complexes of the aryl- and anthracenyl-linked Schiff-base macrocyclic ligands L^Me and L^A were synthesised by reaction of UO₂(H₂L) with M{N(SiMe₃)₂}₂ (M = Ge, Sn, Pb). For complexes of the anthracenyl-linked ligand (L^A) the group 14 metal sits out of the N₄-donor plane by up to 0.7 Å resulting in relatively short M⋯OUO distances which decrease down the group; however, the solid state structures and IR spectroscopic analyses suggest little interaction occurs between the oxo and group 14 metal. In contrast, the smaller aryl-linked ligand (L^Me) enforces greater interaction between the metals; only the Pb^II complex was cleanly accessible although this complex was relatively unstable in the presence of HN(SiMe₃)₂ and some organic oxidants. In this case, the equatorial coordination of pyridine-N-oxide causes a 0.08 Å elongation of the endo UO bond and a clear interaction of the uranyl ion with the Pb(II) cation in the second donor compartment.