SYNTHESIS OF MULTIDENTATE SCHIFF BASE LIGANDS. CRYSTAL STRUCTURE OF (N-N’-BIS(3-ETHOXYSALICYLIDENE)-1,3-DIAMINO-2,2- DIMETHYLPROPANE M. A. Vázquez- Fernández, M. I. Fernández, B. Fernández, A. M. González-Noya, M. Maneiro, M. J. Rodríguez-Doutón Dpto. de Química Inorgánica. Facultad de Ciencias. Univ. de Santiago de Compostela. 27002 Lugo (Spain). ABSTRACT The hexadentate Schiff base ligands were prepared by condensation of 3-ethoxy-2- hydroxybenzaldehyde and different diamines (1,3-diaminopropane, 1,3-diamino-2,2-dimethylpropane, 1,4-diaminobutane) to yield H 2 L n (H 2 L 1 , H 2 L 2 and H 2 L 3 , respectively). The ligands have been characterised by elemental analysis, IR, 1 H and 13 C NMR spectroscopies and mass spectrometry (ES). The crystal structure of the H 2 L 2 ligand was solved by X-ray crystallography, revealing its ability to bind metal centres. INTRODUCTION Our interest in this kind of dicompartmental ligands derives from the known ability of ligands containing six potencial donor atoms to stabilise high oxidation states of metal ions. These ligands present adequate conditions to be useful in the synthesis of octahedral complexes, occupying the equatorial positions around the metal centre. In previous papers we reported the synthesis, structures and properties of Mn (III) complexes with Schiff base ligands 1,2 . At this goal we have designed the dianionic ligands, H 2 L n , that contain an inner site with N- and O- donor atoms (two imine nitrogen and two phenol oxygen atoms) and an outer coordination site with four O- donor atoms (two phenoxo and two ethoxy groups). RESULTS AND DISCUSSION The hexadentate Schiff bases H 2 L n were prepared according to the literature 3 , by condensation of the appropriate diamine with 3-ethoxy-2-hydroxybenzaldehyde in methanol. This mixture was heated at reflux in a round-bottomed flask fitted with a Dean Stark trap to remove the water produced during the reaction. After heating for 3 h, the solution was concentrated to yield a yellow solid. The product was collected by filtration, washed with diethyl ether and dried in air. White crystals of H 2 L 2 , suitable for single crystal X-ray diffraction studies, were obtained by slow evaporation of the methanol solution of the ligand. The characteristiques of the ligands are: Ligand H 2 L 1 : M.p. 81.7 ºC. Anal. Calc. for C 21 H 26 N 2 O 4 : C, 68.1; H, 7.1; N, 7.6. Found: C, 68.2; H, 7.2; N, 7.6%. MS ES (m/z): 371; IR (KBr, cm -1 ): ν(O-H) 3250, ν(C=N) 1632, ν(C-O) 1251. 1 H NMR (DMSO-d 6 , ppm): δ 8.35 (s, 2H), 6.77-6.92 (m, 6H), 4.10 (c, 4H), 3.72 (t, 4H), 2.08 (t, 2H), 1.47 (t, 6H). 13 C NMR (DMSO-d 6 , ppm): δ 165.8 (C=N), 152.2 (C-OCH 2 CH 3 ), 147.9 (C-OH), 31.9 (CH 2 ). Ligand H 2 L 2 : M.p. 98 ºC. Anal Calc. for C 23 H 30 N 2 O 4 : C, 69.3; H, 7.6; N, 7.1. Found: C, 69.2; H, 7.7; N, 7.1%. MS ES (m/z): 399; IR (KBr, cm -1 ): ν(O-H) 3437, ν(C=N) 1637, ν(C-O) 1248. 1 H NMR (DMSO-d 6 , ppm): δ 8.50 (s, 2H), 6.71-7.02 (m, 6H), 4.01 (m, 4H), 3.52 (s, 4H), 1.32 (m, 6H), 0.90 (s, 6H). 13 C NMR (DMSO-d 6 , ppm): δ 167.5 (C=N), 147.9 (C-OCH 2 CH 3 ), 152.6 (C-OH), 24.3 (CH 3 ). Ligand H 2 L 3 : M.p. 135.4 ºC. Anal Calc. for C 22 H 28 N 2 O 4 : C, 68.7, H, 7.3; N, 7.3. Found: C, 68.9; H, 7.4; N, 7.3%. MS ES (m/z): 385; IR (KBr, cm -1 ): ν(O-H) 3242, ν(C=N) 1624, ν(C-O) 1251. 1 H NMR (DMSO-d 6 , ppm): δ 8.32 (s, 2H), 6.80-6.90 (m, 6H), 4.10 (c, 4H), 3.63 (s, 4H), 1.80 (m, 4H), 1.47 (t, 6H). 13 C NMR (DMSO-d 6 , ppm): δ 165.2 (C=N), 152.6 (C-OCH 2 CH 3 ), 148.0 (C-OH), 28.6 (CH 3 ).