Search Results (4)

The trinuclear [Zn₃(PMT)₂(Cl₄)(N₃)₂] complex of the N-pincer ligand, 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine (PMT), was obtained by self-assembly of the polydentate ligand (PMT) with ZnCl₂ in the presence of azide ion as an auxiliary bridging ligand. The X-ray structure analysis revealed a monoclinic crystal system and centrosymmetric space group C2/c. There are two crystallographically independent Zn(II) sites where the Zn1 and Zn2 are tetra- and penta-coordinated with ZnN₂Cl₂ and ZnN₄Cl coordination environments, respectively. The distortion τ₄ and τ₅ parameters for the Zn1 and Zn2 sites are 0.93 and 0.52, respectively. Hence, the Zn(1)N₂Cl₂ has a distorted tetrahedral configuration, while the Zn(2)N₄Cl coordination sphere is intermediate between the square pyramidal and trigonal bipyramidal configurations. In this complex, the PMT is a tridentate N-chelate, while the chloride and azide anions are terminal and μ(1,1) bridged ligands, respectively. The %H…H, N…H, Cl…H, and C…H are 40.8, 17.2, 16.0, and 10.1%, respectively, based on Hirshfeld analysis. The charges at the Zn1 (+0.996 e) and Zn2 (+1.067 e) sites are calculated to be less than the official charge of the isolated Zn(II) ion. The μ(1,1) bridged azide has two asymmetric N–N bonds with clear covalent characters. In contrast, the Zn–N and Zn–Cl bonds have predominant closed-shell characters. Full article

A number of novel heteroligand Zn(II) complexes (1–8) of the general type (Lⁿ)Zn(NN) containing O,N,O′-, O,N,S-donor redox-active Schiff bases and neutral N,N′-chelating ligands (NN) were synthesized. The target Schiff bases LⁿH₂ were obtained as a result of the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with substituted o-aminophenols or o-aminothiophenol. These ligands with combination with 2,2′-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion. The molecular structures of complexes 4∙H₂O, 6, and 8 in crystal state were determined by means of single-crystal X-ray analysis. In the prepared complexes, the redox-active Schiff bases are in the form of doubly deprotonated dianions and act as chelating tridentate ligands. Complexes 6 and 8 possess a strongly distorted pentacoordinate geometry while 4∙H₂O is hexacoordinate and contains water molecule coordinated to the central zinc atom. The electrochemical properties of zinc(II) complexes were studied by the cyclic voltammetry. For the studied complexes, O,N,O′- or O,N,S-donor Schiff base ligands are predominantly involved in electrochemical transformations in the anodic region, while the N,N′-coordinated neutral nitrogen donor ligands demonstrate the electrochemical activity in the cathode potential range. A feature of complexes 5 and 8 with sterically hindered tert-butyl groups is the possibility of the formation of relatively stable monocation and monoanion forms under electrochemical conditions. The values of the energy gap between the boundary redox orbitals were determined by electrochemical and spectral methods. The parameters obtained in the first case vary from 1.97 to 2.42 eV, while the optical bang gap reaches 2.87 eV. Full article

New complexes of trivalent cobalt with substituted thiosemicarbazone ligands having an NNS donor system {HL¹ = 4-(4-nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide and HL² = 4-(2,5-dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide} were synthesized via the in situ oxidation of divalent cobalt chloride accompanying its addition to the ligands. The complexes C1 and C2 were characterized via elemental (CHNS) analysis and ¹H NMR, FT-IR and UV-Vis. spectroscopic data. Further, conductometric studies on the DMF solutions of the complexes indicated their 1:1 nature, and their diamagnetism revealed the low-spin trivalent oxidation state of the cobalt in the complexes. The X-ray diffraction analysis of complex C1 indicated that it crystallizes in the triclinic space group P-1. The metal exhibits an octahedral environment built by two anionic ligands bound via pyridine nitrogen, imine nitrogen and thiol sulfur atoms. The complex is counterbalanced by a chloride ion. In addition, two lattice water molecules were detected in the asymmetric unit of the unit cell. The ligand HL² (20 mg/mL in DMSO) displayed inhibition zones of 10 mm against both S. aureus and E. coli, and the same concentration of the respective complex raised this activity to 15 and 12 mm against these bacterial strains, respectively. As a comparison, ampicillin inhibited these bacterial strains by 21 and 25 mm, respectively. Screening assay by HL¹ on four human cancer cells revealed the most enhanced activity against the breast MCF-7 cells. The induced growth inhibitions in the MCF-7 cells by all compounds (0–100 μg/mL) have been detected. The ligands {HL¹ and HL²} and complex C2 gave inhibitions with IC₅₀ values of 52.4, 145.4 and 49.9 μM, respectively. These results are more meaningful in comparison with similar cobalt complexes, but less efficient compared with the inhibition with IC₅₀ of 9.66 μM afforded by doxorubicin. In addition, doxorubicin, HL¹ and HL² induced cytotoxicity towards healthy BHK cells with IC₅₀ values of 36.42, 54.8 and 110.6 μM, but surviving fractions of 66.1% and 62.7% of these cells were detected corresponding to a concentration of 100 μg/mL of the complexes (136.8 μM of C1 and 131.4 μM of C2). Full article

The synthesis, characterization and reactivity of several bi- and tridentate, N-ligated manganese carbonyl trifluoromethyl complexes are presented. These complexes exhibit elongated Mn–C_CF3 bonds (versus Mn(CF₃)(CO)₅), suggesting a lability that could be utilized for the transfer or insertion of the CF₃ functional group into organic substrates. Unlike their Mn–X congeners (X = Cl, Br), these Mn–CF₃ complexes exhibit a preference for hard donor ancillary ligands, thus enabling the synthesis of 4 N-ligated Mn–CF₃ complexes including a mixed-donor tridentate complex using an NNS Schiff base ([2-(methylthio)-N-(1-(pyridin-2-yl)ethylidene)aniline]). Although we have not yet identified efficient CF₃ transfer reactions, fluoride abstraction from the Mn–CF₃ complexes using trimethylsilyl triflate affords the first stable Mn fluorocarbenes as evidenced by ¹⁹F NMR spectroscopy. Full article