The structure of the Zn(II) complex of 5-caffeoylquinic acid (chlorogenic acid, 5-CQA) and the type of interaction between the Zn(II) cation and the ligand were studied by means of various experimental and theoretical methods, i.e., electronic absorption spectroscopy UV/Vis, infrared spectroscopy FT-IR, elemental, thermogravimetric and density functional theory (DFT) calculations at B3LYP/6-31G(d) level. DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), FRAP (ferric reducing antioxidant power), CUPRAC (cupric reducing antioxidant power) and trolox oxidation assays were applied in study of the anti-/pro-oxidant properties of Zn(II) 5-CQA and 5-CQA. The antimicrobial activity of these compounds against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Salmonella enteritidis and Candida albicans was tested. An effect of Zn(II) chelation by chlorogenic acid on the anti-/pro-oxidant and antimicrobial activities of the ligand was discussed. Moreover, the mechanism of the antioxidant properties of Zn(II) 5-CQA and 5-CQA were studied on the basis of the theoretical energy descriptors and thermochemical parameters. Zn(II) chlorogenate showed better antioxidant activity than chlorogenic acid and commonly applied natural (L-ascorbic acid) and synthetic antioxidants (butylated hydroxyanisol (BHA) and butylated hydroxytoluene (BHT)). The pro-oxidant activity of Zn(II) 5-CQA was higher than the ligand and increased with the rise of the compound concentration The type of Zn(II) coordination by the chlorogenate ligand strongly affected the antioxidant activity of the complex.

The metal–organic frameworks of the formula Ln(bta)·nH₂O where n = 3, 4, 5 or 6; bta = benzene-1,3,5-triacetate ion: [C₉H₉(COO)₃]³⁻; Ln = La(III), Nd(III), Eu(III), Tb(III), Ho(III), Tm(III), Lu(III) were synthesized by the reaction of LnCl₃·xH₂O with ammonium salt of H₃bta acid in water solution. Insoluble water compounds crystallize in the monoclinic or triclinic crystal system, and they are stable up to 30 °C. When heated, they decompose up to 160–200 °C in two stages to stable anhydrous compounds. The dehydrated compounds Ln(bta) are still crystalline and stable up to about 350 °C. When heated above 350 °C, they undergo decomposition where the intermediate products are Ln₂O₂CO₃ or Tb₄O₆CO₃ and the residues are: Ln₂O₃ or Tb₄O₇. The interpretation of IR spectra of title compounds was made taking into consideration the experimental and theoretical wavenumbers obtained for H₃bta specie. The XPS spectra of H₃bta and its complexes were recorded. The way of metal–carboxylate group of ligand coordination was discussed. This work presents the results of the XPS analyses, which allowed to determine the binding energies (E _b) for the main lines of Ln3d, Ln4d, Ln5p, C1s, O1s spectra, spin–orbital splitting and full width at half maximum complexes.

Complexes of chlorogenic acid (5-CQA) with copper(II) and iron(III) were synthesized in a solid state and examined by means of FT-IR, thermogravimetric, and elemental analyses. The molar stoichiometric ratios of metal:ligand for the solid forms of the complexes were established as Cu(II):L = 1:2 and Fe(III):L = 2:3 (L: 5-CQA), with the possible coordination through the carboxylate group and the hydroxyl group from the catechol moiety. In an aqueous solution at pH = 7.4, the composition of the complexes was Cu(II):L = 1:1, and Fe(III):L = 1:1 and 1:2. The Cu(II) and Fe(III) complexes with 5-CQA showed lower antioxidant properties, as estimated by the spectrophotometric methods with DPPH^•, ABTS^•+, and HO^• radicals, than the ligand alone, whereas in the lipid peroxidation inhibition assay, the metal complexes revealed a higher antioxidant activity than 5-CQA. Cu(II) 5-CQA showed the highest pro-oxidant activity in the Trolox oxidation assays compared to the other studied compounds. The lipophilic parameters of the compounds were estimated using the HPLC method. 5-CQA and its complexes with Fe(III) and Cu(II) were not toxic to HaCaT cells in a tested concentration range of 0.15–1000 nM after a 24 h incubation time.

The reaction of sodium hydroxide with 2-aminoterephthalic acid leads to the formation of a complex of the general formula: [Na₂(atpt)(H₂O)₅]·H₂O, where atpt = [NH₂C₆H₃(COO)₂]²⁻. Sodium 2-aminoterephthalate was synthesized and characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, thermal analysis and coupled TG–FT-IR technique. Crystallographic study of the sodium complex reveals that the compound crystallizes in the triclinic system, the space group P-1 with a = 7.983(3) Å, b = 8.405(3) Å, c = 11.311(5) Å, α = 70.74(3)°, β = 76.57(3)°, γ = 83.12(3)° and V = 696.1(5) ų. On heating in air atmosphere the compound in question loses all water molecules in two steps in the temperature range 30–205 °C. The anhydrous form of the complex is stable up to 370 °C and then decomposes to sodium carbonate.