Functionalized acyclic Schiff bases and related complexes with d- and f-metal ions

Article abstract of DOI:10.1016/s0020-1693(97)05909-4

The condensation reaction in acetonitrile of 2.6-diformyl-4-chlorophenol with tris-(2-aminoethyl)amine forms the |3+1| macroacyclic Schiff base H₃-I which reacts with LnCl₃·nH₂O (Ln=La³⁺ . Dy³⁺ . Gd³⁺) in the presence of NEt₃ giving rise to Ln(I) · nS (S=H₂O, dmf, CH₃CN:n=0-1.5). Crystals of La(I) (dmf), grown from a dimethylformamide/acetonitrile solution, are monoclinic, space group P2_|/c with a=12.590(4). b=14.277(5), c=19.710(5) A?, β=95.45° and Z=2. This complex is a dimeric entity and shows an inversion center in between the two lanthanum(III) ions. The organic ligand coordinates to one lanthanum ion through the four nitrogen and the three phenoxide oxygen atoms while it links the second lanthanum ion through one aldehydic oxygen atom; the other two aldehydic oxygens are not involved in the coordination and do not form significative interactions with neighboring molecules. Thus each dinuclear complex behaves as an isolated entity. The nonacoordination around each metal ion is reached through the additional coordination of the oxygen atom of a dimethylformamide molecule. The three La-N (iminic) bond distances tall between 2.70 and 2.79 A, while the La-N (aminic) bond is longer (2.86 A?). Similarly the La-O (phenolic) bonds distances are in the range 2.41-2.47 A?, considerably shorter than the La-O (aldehydic) which is 2.72 A?, while the La-O (dimethylformamide) is 2.55 A?. Finally the two lanthanum atoms are 8.24 A apart. 2.6-Diformyl-4-chlorophenol reacts in CH₃CN with H₂N-R-NH₂ to give the |2-1| acyclic Schiff bases H₂-II. The corresponding complexes containing a d (nickel(II) Ni(II), or manganese(III) Mn(II)(OH), an f (lanthanum(III), gadolinium(III), dysprosium(III)) Ln(H₂-II) (NO₃)₃ or the uranyl(VI) ion, UO₂(II) (MeOH), UO₂(H-II) (NO₃) and UO₂(H₂-II) (NO₃)₂ have also been prepared by reaction of these ligands with the appropriate metal salts or by template procedure, the different content of the nitrate in the uranyl(VI) complexes depending on the amount of base used. These complexes may be converted into the acetal analogues in alcoholic solution. Similarly the condensation of 3-methoxy-2-hydroxybenzaldehyde or 3-ethoxy-2-hydroxybenzaldehyde with tris-(2-aminoethyl)amine in a 1:3 molar ratio afforded the |3+1| Schiff bases H₃-IV and H₃-V which react with lanthanide(III) salt to give rise, respectively, in the presence or in the absence of the appropriate amount of base, to Ln(IV) · nH₂O and Ln(V) ·nH₂O and Ln(H₃IV) (X)₃ · nH₂ or Ln(H₃-V) (X)₃ · nH₂O (Ln=³⁺ . Gd³⁺ : X=Cl . NO₃° : n=1-5). These complexes are no longer stable in solution and hydrolyzed especially when redissolved in alcohol. H₃I, H₂-II and/or the related complexes have been engaged in further condensation reactions with 2-aminomethyl-12-crown-4 or 2-aminomethyl-15-crown-5 to give rise to the functionalized Schiff bases (H₃-III and H₂-VII) and related d-or f-complexes. Moreover the functionalized ligands H₃VI, H₂-VIII, H₂-X and H₂-XI and/or the related d-or f-complexes have been synthesized by condensation of the appropriate formyl and amine precursors. The ligands and the complexes have been characterized by physico-chemical measurements, especially by IR and NMR spectroscopy. SEM and EDX investigation, and FAB mass spectrometry.