Axial Ligand exchange in chiral macrocyclic ytterbium(III) complexes.

We investigate the role of axial ligands on the near-IR-optical and paramagnetic NMR spectra of the complex [YbL] + 3 where L is the stereodefined enantiopure chiral macrocycle (L = hexaazapentacyclo[25.3.1.1 1 2 , 2 4 .0 4 , 9 .0 1 9 , 2 4 ]-dotriaconta-1(31),2,10,12,14,16(32),17,25,27,29-decaene). The conformation in solution of the lanthanide complex is characterized by analyzing the pseudocontact 1 H NMR shifts and is consistent with X-ray data of single crystal of analogue systems. The macrocycle is confined within a thin equatorial disk, leaving the cation open to at least two axial sites, on the opposite hemispheres. We recorded, assigned, and analyzed the 1 H NMR spectra of several species upon changing the anion in solution, calculating the magnetic susceptibility anisotropy tensor for each. Near-IR circular dichroism is used to investigate the solution equilibria involving the competing ligands and to derive a spectroscopic series for Yb.