Synthetic, electrochemical and structural aspects of ß-diketonato and carboxylate complexes of aluminium

English: A series of ferrocene-containing tris-β-diketonato aluminium(III) complexes of the form Al(FcCOCHCOR)3 (R = CF3, CH3, C6H5, Fc with Fc = ferrocenyl) were synthesized and subjected to structural and electrochemical investigations. 1H NMR-spectroscopy distinguished between the mer and fac isomers of (FcCOCHCOPh)3 and Al(FcCOCHCOCH3)3. Al(FcCOCHCOCF3)3 existed only as the mer-isomer. A single crystal X-ray crystallographic determination of the structure of Al(FcCOCHCOCF3)3 confirmed the existence of the mer-isomer (Z = 4, space group P212121). All Fc/Fc+ electrochemical couples of Al(FcCOCHCOR)3 could be resolved cyclic voltammetrically. For R = Fc, formal reduction potentials of the ferrocenyl group were found to be Eo′ = 33, 123, 304, 432, 583 and 741 mV versus free ferrocene respectively. A cytotoxic study showed that aluminium(III) has an inhibiting effect on the cytotoxicity of ferrocenecontaining β-diketones. Aluminium formate and acetate were synthesized from γ-Al2O3 as aluminium source and the carboxylate bonding modes identified by FTIR. Dodecanoato and octadecanoato alumoxane as well as aluminium dodecanoate, pentadecanoate, octadecanoate and ferrocenoate were synthesized from the corresponding potassium carboxylate salts and aluminium trisisopropoxide. All complexes were characterized by FTIR and elemental analysis. It was difficult but not impossible to synthesize polymeric aluminium carboxylates with a 1:3 ratio of aluminium:carboxylic acid. It was found that the mode of carboxylate coordination to aluminium may be predicted by FTIR analyses. The difference in C=O stretching frequencies, Δν = νantisymmetric - νsymmetric > 200 cm-1 indicate monodentate coordination. If 80 < Δν < 120 the bonding mode is bridging, while 60 < Δν < 70 indicate bidentate coordination. Asymmetric bidentate or monodentate coordination modes occur when 160 < Δν < 190 cm-1 .