2‐Hydroxybenzaldehyde‐4‐allyl‐S‐methylisothiosemicarbazone and Cu (II), Co (III), Fe (III) and Cr (III) complexes were synthesized and characterized. The new obtained compounds were investigated by elemental analysis, magnetic susceptibility measurements, molar electric conductivity, IR, ¹H NMR, ¹³C NMR, UV–Vis spectroscopy. In addition, the structure of the ligand and six complexes has been determined by single‐crystal X‐ray diffraction analysis. The Cu atom in complex 3 is penta‐coordinated in a distorted square–pyramidal coordination geometry, while the metals in complexes 5–9 are in a distorted octahedral environment. For all compounds the antimicrobial activity was studied on a series of standard strains, such as Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Salmonella abony and Candida albicans. The in vitro antiproliferative activity of the ligand and complexes was screened on human leukemia HL‐60 cells, human cervical epithelial HeLa cells, human epithelial pancreatic adenocarcinoma BxPC‐3 cells, human muscle rhabdomyosarcoma spindle and large multinucleated RD cells. The primary screening on a wider series of cancer cells showed that copper coordination compound 2 manifests high activity towards HeLa, BxPC‐3 and RD cancer cells, which is three–six times higher than the activity of doxorubicin. The selectivity index that is the ratio between the IC₅₀ value for the normal MDCK cells and IC₅₀ values for the cancer cells varies in the range 2.44–21.17. This index is 5.5–11 times higher for the copper coordination compound 2 than for the doxorubicin. Cr (III), Fe (III) and Co (III) coordination compounds 6–9 manifest high antioxidant activity towards ABTS^•+ that exceeds 47–67 times the activity of Trolox.

A series of zinc(II) ([Zn(H₂O)(L)Cl] (1)), copper (II) ([Cu(L)Cl] (2), [Cu(L)Br] (3), [Cu₂(L)₂(CH₃COO)₂]·4H₂O (4)), nickel(II) ([Ni(HL)₂]Cl₂·H₂O (5)), and cobalt(III) ([Co(L)₂]Cl (6)) complexes were obtained with 2‐formylpyridine N⁴‐allylthiosemicarbazone (HL). In addition another two thiosemicarbazones (3‐formylpyridine N⁴‐allylthiosemicarbazone (HL^a) and 4‐formylpyridine N⁴‐allylthiosemicarbazone (HL^b)) have been obtained. The synthesized thiosemicarbazones have been studied using ¹H and ¹³C NMR spectroscopy, IR spectroscopy, and X‐ray diffraction analysis. The composition and structure of complexes were studied using elemental analysis, IR and UV‐Vis spectroscopies, molar conductivity, and magnetic susceptibility measurements. Single crystal X‐ray diffraction analysis elucidated the structure of thiosemicarbazones HL, HL^a, and HL^b, as well as complexes 4 and 5. The antiproliferative properties of these compounds toward a series of cancer cell lines (HL‐60, HeLa, BxPC‐3, RD) and a normal cell line (MDCK) have been investigated. The nickel complex shows high selectivity (SI > 1000) toward HL‐60 cell line and is the least toxic. The zinc complex shows the highest selectivity toward RD cell line (SI = 640). The copper complexes (2–4) are the most active molecular inhibitors of proliferation of cancer cells, but exhibit not such a high selectivity and are significantly more toxic. Zinc and copper complexes manifest high antibacterial activity. It was found that calculated at B3LYP level of theory different reactivity descriptors of studied compounds strongly correlate with their biological activity.

New zinc (II), copper (II), nickel (II) and cobalt (III) complexes, [Zn (HL)₂]I₂ (1), [Cu (HL)Cl₂] (2), [Cu (HL)Br₂] (3), [Cu (HL)(H₂O)₂](ClO₄)₂ (4), [Ni (HL)₂]I₂·H₂O (5), [Co(L)₂]Cl (6), [Co(L)₂]NO₃ (7), [Co(L)₂]I·[Co(L)₂](I₃) (8) were obtained with 2‐formylpyridine 4‐allyl‐S‐methylisothiosemicarbazone (HL). The isothiosemicarbazone ligand was characterized by NMR (¹H and ¹³C), IR spectroscopy and X‐ray diffraction. All the complexes were characterized by elemental analysis, IR, UV–Vis, ESI‐MS spectroscopy, molar conductivity, magnetic susceptibility measurements. X‐ray diffraction analysis on the monocrystal and powder elucidated the structure of the complexes 1, 5, 7 and 8.The ligand and the complexes were tested for their antioxidant and antimicrobial activity against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Candida albicans. Also, the antiproliferative properties of these compounds on human leukemia HL‐60, human cervical epithelial HeLa, human epithelial pancreatic adenocarcinoma BxPC‐3, human muscle rhabdomyosarcoma spindle, large multinucleated RD cells and normal MDCK cells have been investigated. The nickel complex 5 and cobalt complexes 6, 7 showed promising antiproliferative activity and low toxicity.

The eleven new copper(II) and nickel(II) coordination compounds [Cu(L)Br]₂ (1), [Cu(L)Cl] (2), [Cu(L)NO₃] (3), [Ni(L)Cl] (4), [Ni(HL)₂](NO₃)₂ (5), and [Cu(A)(L)]NO₃, where A is 1,10-phenanthroline (6), 2,2′-bipyridine (7), 3,4-dimethylpyridine (8), 3-methylpyridine (9), pyridine (10) and imidazole (11) were synthesized with 3-(morpholin-4-yl)propane-2,3-dione 4-allylthiosemicarbazone (HL). The new thiosemicarbazone was characterized by NMR and FTIR spectroscopy. All the coordination compounds were characterized by elemental analysis and FTIR spectroscopy. Also, the crystal structures of HL and complexes 1, 6, 7, and 11 were determined using single-crystal X-ray diffraction analysis. Complex 1 has a dimeric molecular structure with two bromide bridging ligands, while 6, 7, and 11 are ionic compounds and comprise monomeric complex cations. The studied complexes manifest antibacterial and antifungal activities and also have an antiradical activity that, in many cases, surpasses the activity of trolox, which is used as a standard antioxidant in medicine. Copper complexes 1–3 have very weak antiradical properties (IC₅₀ > 100 µM), but nickel complexes 4–5 are strong antiradicals with IC₅₀ values lower than that of trolox. The mixed ligand copper complexes with additional ligand of N-heteroaromatic base are superior to complexes without these additional ligands. They are 1.4–5 times more active than trolox.

The six new copper(II) coordination compounds [Cu(HL¹)Cl₂] (1), [Cu(HL¹)Br₂] (2), [Cu(H₂O)(L¹)(CH₃COO)]·1.75H₂O (3), [Cu(HL²)Cl₂] (4), [Cu(HL²)Br₂] (5), [Cu(H₂O)(L²)(CH₃COO)] (6) were synthesized with 2-formyl- and 2-acetylpyridine N⁴,S-diallylisothiosemicarbazones (HL¹ and HL²). The new isothiosemicarbazones were characterized by NMR, FTIR spectroscopy, and X-ray crystallography ([H₂L²]I). All copper(II) coordination compounds were characterized by elemental analysis, FTIR spectroscopy, and molar conductivity of their 1mM methanol solutions. Furthermore, the crystal structure of complex 3 was determined using single-crystal X-ray diffraction analysis. The studied complexes manifest antibacterial and antifungal activities, that in many cases are close to the activity of medical drugs used in this area, and in some cases even exceed them. The complexes 4 and 5 showed the highest indexes of selectivity (280 and 154) and high antiproliferative activity against BxPC-3 cell lines that surpass the activity of Doxorubicin. The complexes 1–3 also manifest antioxidant activities against cation radicals ABTS^•+ that are close to that of trolox, the antioxidant agent used in medicine.