Solid state structures and solution behaviour of tetranuclear lanthanide(iii) carbonate-bridged coordination compounds of chiral 3+3 amine macrocycle

The linking of two dinuclear macrocyclic units of large triphenolic hexaazamine by two carbonate anions results in the formation of dimeric tetranuclear Sm(III), Eu(III) and Gd(III) complexes. These complexes were initially obtained serendipitously by fixation of atmospheric carbon dioxide and subsequently obtained in a rational way by the application of carbonate salts. The X-ray crystal structures of these isomorphic complexes show highly folded conformation of the macrocycle. This type of conformation is also confirmed by 2D NMR spectra of the Sm(III) complex. The ESI-MS and NMR spectra reveal also that these carbonate complexes exist in solution in two different forms that are in a concentration-dependent dynamic equilibrium.

Automated summary

The formation of dimeric tetranuclear Sm(III), Eu(III), and Gd(III) complexes occurs when two dinuclear macrocyclic units of large triphenolic hexaazamine are linked by two carbonate anions. These complexes were initially obtained accidentally by fixing atmospheric carbon dioxide and subsequently obtained in a deliberate manner using carbonate salts. The X-ray crystal structures of these isomorphic complexes reveal a highly folded conformation of the macrocycle, which is also confirmed by 2D NMR spectra of the Sm(III) complex. ESI-MS and NMR spectra indicate that these carbonate complexes exist in solution in two different forms that are in a concentration-dependent dynamic equilibrium.