Structural determinations of carbamato-bridging ligands derived from atmospheric CO2 in 3d–4f complexes

Abstract

1H and 13C NMR studies demonstrate that in a reaction involving a Zn–La complex and piperidine as an organic base, a 1-piperidinecarboxylate unit is formed in situ and assimilated by the complex as a ligand. Existence of this ligand is confirmed by structural determinations of two related Ni–Gd and Ni–Tb complexes. We highlight that the observed capture of the CO2 derivative is not metal or ligand dependent but that the presence of a base in the reaction medium is the key parameter of the assimilation of CO2 by 3d–4f bimetallic complexes. The propensity of amines for carbonatation is responsible for the formation of these anionic ligands, while the 3d–4f complexes act only as trapping entities.