Solid state and solution properties of lanthanide(III) complexes of a tetraiminodiphenolate macrocyclic ligand. X-ray structure, 1H NMR and luminescence spectral studies

The lanthanide(III) complexes of composition [Ln(LH2)(H2O)3Cl]Cl2 (Ln = La–Lu and Y, 1–15) derived from the tetraiminodiphenolate macrocyclic ligand L2− have been prepared and characterized. In these compounds, the two uncoordinated imine nitrogens of the macrocycle are protonated and hydrogen-bonded with the metal-bound phenolate oxygens and thereby provide a zwitterionic structure to the ligand. The X-ray crystal structure of the compounds of La and Nd have been determined and they are found to be isostructural. The coordination polyhedra for the eight-coordinated metal centre in the complex cation [Ln(N2O2)(O3Cl)]2+ can be described as distorted square antiprism. Intermolecular hydrogen-bondings involving the three coordinated water molecules and the two uncoordinated chloride ions give rise to the 2-D network in which the chlorides are triply hydrogen-bridged and the water molecules are doubly hydrogen-bridged. Moreover, the aromatic rings in this network are involved in π–π interaction in two different ways. 1H NMR spectra of the complexes in (CD3)2SO have been studied. The spectral assignments for the paramagnetic complexes of Ce–Eu have been made from {1H–1H} COSY spectra and longitudinal relaxation time (T1) measurements. It is inferred that the complex species [Ln(LH2){(CD3)2SO}4]3+ that exist in solution are isostructural for the compounds of La–Eu. The contact and pseudo-contact contribution to the isotropic paramagnetic shifts in the complexes of Ce–Eu have been estimated. The luminescence spectra of the complexes of La, Sm, Eu and Tb have been studied in methanol–ethanol (1:4) glassy matrix and in the solid state at 77 K, and the quantum yields have been estimated.