Synthesis, X-ray structure, and solution NMR studies of Ln(III) complexes with a macrocyclic asymmetric compartmental Schiff base. Preference of the Ln(III) ions for a crown-like coordination site

The compartmental ligand H2LA, containing an N3O2 Schiff base and an O2O3 c rown like coordination site, has been prepared by reaction of 3,3'-(3-oxape ntane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) with 1,5-diamino-3-azamethyl pentane. The formation of a [1+1] macrocycle was inferred by IR, NMR, and m ass spectrometry. When reacted with the rare-earth hydrate chlorides, LnCl( 3). nH(2)O (Ln = La, Ce, Pr, Nd, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y), H2LA o r its precursors (template reaction) form the mononuclear complexes [Ln(H2L A)(H2O)(4)]Cl-3. nH(2)O where the lanthanide ion coordinates the O2O3 crown like site. The solid-state X-ray structures of [Ln(H2LA)(H2O)(4)]Cl3 . nH2 O (Ln = Ce, Dy, Lu) have been determined. [Lu(H2LA)(H2O)(4)]Cl-3. 3H(2)O is monoclinic space group P2(1)/n (Z = 4) with a = 15.269(5) Angstrom, b = 11 .484(5) Angstrom, c = 19.389(6) Angstrom, beta = 102.85(5)degrees; [Ce(H2LA )(H2O)(4)]Cl-3. H2O and [Dy(H2LA)(H2O)(4)]Cl-3. H2O are isomorphous, space group P2(1) (Z = 2), with a 10.959(5) Angstrom, b = 16.978(5) Angstrom, c = 9.017(4) Angstrom, beta = 97.73(5)degrees, and a = 10.874(5) Angstrom, b = 16.797(5) Angstrom, c = 9.046(4) Angstrom, beta = 97.86(5)degrees for the cerium and dysprosium complexes, respectively. In the three compounds the m etal ion is coordinated in a similar manner by the five oxygens (two phenol ic and three etheric) of the cyclic ligand and the nine coordination around the central atom is reached by the oxygen atoms of four coordinated water molecules. Three chlorine ions are present in the asymmetric unit. A detail ed H-1 NMR study was carried out in CD3OD for both the diamagnetic and para magnetic [Ln(H2LA)(H2O)(4)]Cl-3 complexes in order to compare their structu re in solution with that found in the solid state. The quantitative analysi s of the paramagnetic proton shifts indicates that the complexes from La to Tm are isostructural, maintain in solution the same type of coordination p olyhedron found at the solid state, with the metal ion invariably coordinat ed in the O2O3 compartment, and present a high degree of stereochemical non rigidity. In the case of the Lu complex, the decreased fluxionality due to the reduced ionic radius allows the observation of two isomeric species in the H-1 NMR spectrum at low temperature.