Macrocyclic and macroacyclic compartmental Schiff bases: synthesis, characterization, X-ray structure and interaction with metal ions

Acyclic, potentially hexadentate (H4LA?H4LD) or decadentate (H6LE) compartmental Schiff bases have been obtained by reaction in methanol of 2,3-dihydroxybenzaldehyde and 1,2-diaminoethane, 1,2-diamino-2-methylpropane, 1,3-diamino-2,2-dimethylpropane, 1,2-diaminobenzene or tris(2-aminoethyl)amine in a 2:1 or 3:1 molecular ratios as appropriate. The reaction of 2,6-diformyl-4-Z-phenol (Z?Cl-, CH3-) with 1,2-diaminobenzene in methanol produced the partially reduced macrocycles (H2LF and H2LG). Similarly symmetric tetraimine macrocyclic ligands have been synthesized by cyclo-condensation of the same 2,6-diformyl-4-substituted phenols and 1,5-diamino-3- azapentane (H2LH) or 1,4-bis(3-aminopropyl)piperazine (H2LI). A step by step procedure has been employed for the preparation of the asymmetric macrocycle (H2LL). The ligands are yellow or yellow-orange solids and have been characterized by elemental analyses, IR, 1H NMR spectroscopy and electron impact (EI) or fast atom bombardment (FAB) mass spectrometry. The X-ray crystal structures of H4LC and H2LF have also been solved. Crystals of H4LC, grown from CHCl3, are monoclinic, space group P21/c with a=6.767(4), b=14.106(5), c=18.163(5) Å, ?=91.05(4)° for Z=4. The molecule is composed of two identical dihydroxybenzaldimine moieties connected by the carbon atom C(9). Three hydroxylic oxygens are protonated while the fourth is negatively charged. An intermolecular hydrogen system, involving the hydroxyl groups, gives rise to the formation of polymer chains parallel to c axis. Crystals of H2LF, grown from CHCl3, are monoclinic, space group P21/a with a=22.481(7), b=8.989(5), c=11.911(5) Å, ?93.28(5)° for Z=4. The molecule shows some unexpected bond lengths and angles. Two nitrogen atoms of each molecule are iminic, the other two aminic in character. A reduction of two C?N bonds occurs during the synthetic procedures with the consequent formation of the partially reduced Schiff base. The coordination properties of the acyclic and cyclic ligands towards d and/or f metal ions have been tested, and the results are discussed in detail.