Molecular movements inside [1+1] asymmetric compartmental macrocycles: Formation of positional mononuclear and hetero-dinuclear lanthanide(III) isomers and related homo-dinuclear complexes

Abstract

The mononuclear macrocyclic lanthanide(III) complexes, [Ln(H 2L)(H 2O) 4]Cl 3 (Ln = Y, La, Ce, Cu, Tb, Yb, Lu; H 2L = H 2L A, H 2L B, H 2L C) were prepared by condensation 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)bis(2-hydroxybenzaldehyde) or 3,3′-(3-oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) with 1,5-diamino-3-azamethylpentane or 1,7-diamino-3-azamethylheptane in the presence of LnCl 3 · nH 2O as templating agent. The asymmetric [1+1] ligands H 2L A, H 2L B and H 2L C contain one smaller or larger N 3O 2 Schiff base site and one crown-ether like O 2O 4 or O 2O 3 site. The preference of the lanthanide ion to reside into the Schiff base or the crown-ether like chamber was investigated in the solid state and in methanol or dimethylsulfoxide solution. It was found that in the solid state or in methanol the lanthanide(III) ion coordinates into the O 2O n site while in dimethylsulfoxide demetalation and partial metal ion migration from the O 2O n into the N 3O 2 chamber occur. The mononuclear lanthanide(III) complexes [Ln(H 2L)(H 2O) 4]Cl 3 with the Ln 3+ ion in the O 2O n site have been used as ligands in the synthesis of the heterodinuclear complexes LnLn′(L)(Cl) 4 · 4H 2O by reaction with the appropriate Ln′(III) chloride in methanol and in the presence of base. The related homodinuclear complexes Ln 2(L)(Cl) 4 · 4H 2O have been prepared by the one-pot condensation of the appropriate precursors in the presence of base and of the lanthanide(III) ion as templating agent. The single-crystal X-ray structure of [Eu(H 2L A)(H 2O) 4]Cl 3 · 5H 2O has been determined. The europium ion is nine-coordinated in the O 2O 3 ligand site and bonded to four water molecules and the coordination polyhedron can be described as a square monocapped antiprism. The site occupancy of the different lanthanide(III) ions and the physico-chemical properties arising from the different dinuclear aggregation and/or from the variation of the crown-ether shape have been investigated by IR and NMR spectroscopy, MS spectrometry and SEM-EDS microscopy. In particular, site migration and/or transmetalation reactions, together with demetalation reactions, have been monitored by NMR studies in methanol and dimethylsulfoxide. It was found that these processes strongly depend on the shape of the two coordination chambers, the solvent used and the radius of the lanthanide(III) ions. Thus, these molecular movements can be tuned by changing appropriately these parameters.