Heterodinuclear Ln-Na complexes with an asymmetric macrocyclic compartmental Schiff base

The hetero-dinuclear lanthanide(III)-sodium(I) complexes LnNa(L)(Cl)2 (CH3OH) (Ln= La–Nd, Sm-Lu), where H2L is a [1+1] asymmetric compartmental macrocyclic ligand containing a N3O2 Schiff base and a O3O2 crown-ether- like coordination sites, have been prepared and characterized by IR, 1H-, 13C- and 23Na NMR, mass spectrometry and elemental analysis by electron microscopy. In the solid state the lanthanide(III) ions coordinate the Schiff base N3O2 site and the sodium ion occupies the O3O2 crown-like cavity, as shown by the X-ray crystal structures of the Nd, Eu, Gd and Yb derivatives. In these complexes the lanthanide(III) ion is coordinated by two chlorine atoms in trans position and by three nitrogen and two negatively charged phenol oxygen atoms of the Schiff base, reaching heptacoordination with a pentagonal bipyramidal geometry. The sodium ion is coordinated by three etheric oxygen atoms and the two phenolic oxygens that act as a bridge. A methanol molecule is also coordinated in the apical position of the resulting pentagonal pyramidal polyhedron. A detailed 1H and 13C NMR study was carried out in CD3OD for both diamagnetic and paramagnetic heterodinuclear complexes [LnNa(L)(Cl)2 (CH3OH)]. The complexes are isostructural also in solution and their structures parallel those found in the solid state. Moreover, some significative distances determined in the solid state and in solution are strictly comparable. Finally, the potential use of these complexes as molecular probes for the selective recognition of specific metal ions has been tested. In particular, their ability to act as shift reagents and the selectivity of the O3O2 site towards Li+, Ca2+, and K+ was investigated by 23Na NMR spectroscopy.