The present study describes the coordination properties of a reduced Schiff base, N-(2-hydroxybenzyl)alanine, towards cobalt(II) using potentiometric as well as spectroscopic (UV-Vis and ESI-MS) methods. The results indicate the formation of six mononuclear complexes showing high stability in aqueous solution. Coordination occurs in the {O−phenolic,N,O−carboxyl} and {N,O−carboxyl} chelation modes, depending on the degree of ligand deprotonation. Examination of the complexation equilibria at pH ca 7, which is important from a biological point of view, allowed to identify two species: [CoL] and [CoL2H]−. The kinetic analysis showed a structural change of those cobalt(II) complexes from octahedral to tetrahedral in accordance with a first-order time relationship. The antimicrobial properties of N-(2-hydroxybenzyl)alanine, cobalt(II) nitrate and of the Co(II) – ligand complexes were determined against Gram-positive bacteria (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori) and a fungal strain (Candida). The results indicate that the complexes are more active for more strains than the ligand alone. Nevertheless, the complexes induce a higher decrease in the metabolic activity of cells but without damage to nuclei. Tetrahedral structures show stronger anti-cellular toxicity than octahedral complexes, which is most likely due to the higher accessibility of the cobalt(II) center.

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Methyl 2-methyl-4-oxo-4H-chromene-3-carboxylate (1) was treated with 25% aqueous ammonia to give 3-(1-aminoethylidene)-2H-chromene-2,4(3H)-dione (2). Compound 2 was used as a ligand for the formation of a palladium(II) complex. The structures of the ligand and its palladium complex 3 were determined by IR and 1 H NMR spectroscopy, FAB mass spectrometry and elemental analysis. The single-crystal Xray structure of 3 was also solved. Ligand 2 in 20% dioxane solution shows two protonation constants -log β 11 = 4.28 ± 0.01 and log β 12 = 7.66 ± 0.03. In complex 3 two ligand molecules chelate to the Pd ion through their N and O donors, giving a four-coordinate Pd II center with a cis-N 2 O 2 donor

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