Synthesis and structure investigation of the antibiotic amoxicillin complexes of d-block elements

The study of some transition metals (M) and amoxicillin trihydrate (ACT) ligand complexes (M–ACT) that formed in solution involved the spectrophotometric determination of stoichiometric ratios and their stability constants and these ratios were found to be M:ACT = 1:1, 1:2 and 2:1 in some instances. The calculated stability constants of these chelates, under selected optimum conditions, using molar ratio method have values ranging from Kf = 107 to 1014. These data were confirmed by calculations of their free energy of formation ΔG  , which corresponded to their high stabilities. The separated solid complexes were studied using elemental analyses, IR, reflectance spectra, magnetic measurements, mass spectra and thermal analyses (TGA and DTA). The proposed general formulae of these complexes were found to be ML(H2O)w(H2O)x(OH)y(Cl)zML(H2O)w(H2O)x(OH)y(Cl)z, where M = Fe(II), Co(III), w=0w=0, x = 2, y = 1, z   = 0; M = Co(II), w=0w=0, x = 1, y = 0, z   = 1; M = Fe(III), w=0w=0, x = 1, y = 2, z   = 0; M = Ni(II), Cu(II) and Zn(II), w=2w=2, x = 0, y = 1, z   = 0, where ww = water of crystallization, x = coordinated water, y = coordinated OH− and z = Cl− in the outer sphere of the complex. The IR spectra show a shift of ν(NH) (2968 cm−1) to 2984–2999 cm−1of imino group of the ligand ACT and the absence of ν(CO) (β-lactame) band at 1774 cm−1 and the appearance of the band at 1605–1523 cm−1 in all complexes suggest that 6,7-enolization takes place before coordination of the ligand to the metal ions. The bands of MN (at 625–520 cm−1) and of MO (at 889–7550 cm−1) proved the bond of N (of amino and imino groups) and O of CO group of the ligand to the metal ions. The reflectance spectra and room temperature magnetic measurements refer to octahedral complexes of Fe(II) and Fe(III); square planner form of Co(II), reduced Co(III), Ni(II) and Cu(II)–ACT complexes but tetrahedral form of Zn–ACT complex. The thermal degradation of these complexes is confirmed by their mass spectral fragmentation. These data confirmed the proposed structural and general formulae of these complexes.