The complexation processes of several derivatives of salicylic acid with Fe³⁺, Co²⁺, Cu²⁺, and Zn²⁺ cations have been studied by spectrophotometric titration. According to optimized conditions, complex compounds were isolated, and their spectral characteristics were obtained. Based on spectral analysis, the structures of the complexes were proposed: bidentate chelate coordination of the organic ligands through an ionized hydroxy group and an O atom of a carboxylic group, which follows from FTIR analysis and X-ray crystal structure determination of metal complexes with other α-hydroxy carboxylic acids. In silico studies of biological activity of the isolated complexes in comparison with non-coordinated ligands are reported. The most probable activity is inhibition of the multiprotein complex of the respiratory electron transport chain and antitumor activity, which slightly changes at complexation. A possible way of absorption of 2,3-dihydroxy benzoic acid, 3-methoxy salicylic acid, and their complexes with divalent metals is predicted to be through the gastrointestinal tract as well as 3,5-DNSA and Fe³⁺ complexes cannot be absorbed by organisms.

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