Transition metal complexes with thiosemicarbazide-based ligands. Part 56. Square-pyramidal complexes of copper(II) with 2-acetylpyridine S-methylisothiosemicarbazone

Synthesis, isomerization, and DFT studies of five-membered heterocyclic ketoximes

A homologous series of five-membered heterocyclic ketoximes is synthesized by condensation reactions of 2-acetylpyrrole, 2-acetylthiophene, and 2-acetylfuran with hydroxylamine hydrochloride. These compounds were fully characterized by X-ray single-crystal diffraction, elemental analysis, 1H NMR, IR, UV-Vis, and fluorescence spectra. Interesting isomerization phenomena are observed for these heterocyclic ketoximes by different characterization methods. By means of 1H NMR and X-ray single-crystal diffraction, it was found that 2-acetylpyrrole oxime (1) exists as the Z-type geometric isomer, 2-acetylfuran oxime (3) exists as the E-isomer, while 2-acetylthiophene oxime (2) is identified as a mixture of Z- and E-isomers. To study the above phenomena further, quantum chemical calculations of total energy, dipole moment, EHOMO, ELUMO, and other parameters of each heterocyclic ketoxime were carried out by Density functional theory (DFT). The theoretical calculations were in good accordance with the experimental spectroscopic results.

Crystal structure of 2-acetylpyrrole S-methylthiosemicarbazonium hydroiodide, C8H13IN4S

C8H13IN4S, monoclinic, P21/n (no. 14), a = 5.9563(4) Å, b = 12.8592(8) Å, c = 16.1795(10) Å, β = 99.450(1)°, V = 1222.42(14) Å3, Z = 4, R gt(F) = 0.0228, wR ref(F 2) = 0.0535, T = 296 K.

Co(iii) complexes of (1,3-selenazol-2-yl)hydrazones and their sulphur analogues

The first Co(iii) complexes with (1,3-selenazol-2-yl)hydrazones as an unexplored class of ligands were prepared and characterized by NMR spectroscopy and X-ray diffraction analysis. The novel ligands act as NNN tridentate chelators forming octahedral Co(iii) complexes. The impact of structural changes on ligands' periphery as well as that of isosteric replacement of sulphur with selenium on the electrochemical and electronic absorption features of complexes are explored. To support the experimental data, density functional theory (DFT) calculations were also conducted. Theoretical NMR chemical shifts, the relative energies and natural bond orbital (NBO) analysis are calculated within the DFT approach, while the singlet excited state energies and HOMO-LUMO energy gap were calculated with time-dependent density functional theory (TD-DFT). The electrophilic f^- and nucleophilic f⁺ Fukui functions are well adapted to find the electrophile and nucleophile centres in the molecules. Both (1,3-selenazol-2-yl)- and (1,3-thiazol-2-yl)hydrazone Co(iii) complexes showed potent antimicrobial and antioxidant activity. A significant difference among them was a smaller cytotoxicity of selenium compounds.

Syntheses and structures of discrete copper(II) and cadmium(II) supramolecular complexes based on 1,4-diacylthiosemicarbazone ligands

Thiosemicarbazides and their metal complexes have attracted considerable interest because of their biological activities and their flexibility, which allows the ligands to bend and rotate freely to accommodate the coordination geometries of various metal centres. Discrete copper(II) and cadmium(II) complexes have been prepared by crystallization of N-[2-(2-hydroxybenzoyl)hydrazinecarbonothioyl]propanamide (H3L) with Cu(CH3COO)2 or Cd(NO3)2 in a dimethylformamide/methanol mixed-solvent system at room temperature, affording the complexes di-μ-acetato-bis{μ4-1-[(2-oxidophenyl)carbonyl]-2-(propanamidomethanethioyl)hydrazine-1,2-diido}tetracopper(II) dimethylformamide disolvate, [Cu4(C11H10N3O3S)2(C2H3O2)2]·2C3H7NO, (I), and bis{μ2-[(2-hydroxyphenyl)formamido](propanamidomethanethioyl)azanido}bis[(4,4'-bipyridine)nitratocadmium(II)] dihydrate, [Cd2(C11H12N3O3S)2(NO3)2(C10H8N2)2]·2H2O, (II). Complex (I) consists of four Cu(II) cations, two μ4-bridging trianionic ligands and two μ2-bridging acetate ligands, while complex (II) is composed of two Cd(II) cations, two μ2-bridging monoanionic ligands, two nitrate ligands and two 4,4'-bipyridine ligands. These discrete complexes are connected by hydrogen bonds and van der Waals interactions to form a three-dimensional supramolecular architecture. Compared with (I), the phenolic hydroxy group and hydrazide N atom of the thiosemicarbazide ligand of (II) are not involved in coordination and lead to a binuclear Cd(II) complex. This different coordination mode may be attributed to the larger ionic radius of the Cd(II) ion compared with the Cu(II) ion.

Poly[bis(mu-4-benzoyl-1-isonicotinoylthiosemicarbazide-kappa2N:S)dichloridocadmium(II)]

The asymmetric unit of the title complex, [CdCl(2)(C(14)H(12)N(4)O(2)S)(2)](n), consists of one Cd(II) ion located on the crystallographic inversion centre, one 4-benzoyl-1-isonicotinoylthiosemicarbazide ligand and one chloride ligand. The central Cd(II) ion adopts a distorted octahedral coordination geometry formed by two pyridyl N atoms of two ligands, two S atoms of two other ligands and two chloride ligands. The thiosemicarbazide ligands act as bridges, linking the metal ions into a two-dimensional layered structure parallel to the bc plane. Intermolecular N-H...O hydrogen bonds and C-H...pi interactions exist between adjacent layers.