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

Heterodinuclear 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 site, have been prepared and characterized by IR, ¹H, ¹³C, and ²³Na NMR spectroscopy, mass spectrometry, and electron microscopy. In the solid state, the lanthanide(III) ions coordinate the Schiff-base N₃O₂ site, and the sodium ion occupies the O₃O₂ crownlike 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 the trans position and by three nitrogen and two negatively charged phenol oxygen atoms of the Schiff base, and the ion is heptacoordinated 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 also isostructural 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 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⁺ were investigated by ²³Na NMR spectroscopy.