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

H-1 and C-13 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. (C) 2015 Elsevier Ltd. All rights reserved.