Versatile Coordinative Abilities of a New Hybrid Pteridine−Thiosemicarbazone Ligand: Crystal Structure, Spectroscopic Characterization, and Luminescent Properties

Structural, spectral, thermal and biological studies on (E)-2-(1-(4-hydroxyphenyl)ethylidene)-N-(pyridin-2-yl)hydrazinecarbothioamide and its metal complexes

Schiff base complexes of Mn(II), Co(II), Ni(II), Cu(II), Cd(II), Hg(II) and U(VI)O2 with (E)-2-(1-(4-hydroxyphenyl)ethylidene)-N-(pyridin-2-yl)hydrazinecarbothioamide (H2PHAT) were synthesized and characterized by different physicochemical methods, elemental analysis, (UV-vis, IR and (1)H NMR spectra) and thermal analysis (TG and DTG) techniques. Spectral data showed that H2PHAT behaves as a NS bidentate ligand through both thione sulphur or thiol sulphur and the nitrogen of the pyridine ring or azomethine nitrogen, NSN tridentate ligand through both thione sulphur or thiol sulphur, the nitrogen of the pyridine ring and azomethine nitrogen. ESR spectrum data for Cu(II) solid complex confirms the square planar state is the most fitted one for the coordinated structure. The kinetic parameters were determined for each thermal degradation stage of the complexes using Coats-Redfern and Horowitz-Metzger methods. From modeling studies, the bond length, bond angle, HOMO, LUMO and dipole moment had been calculated to confirm the geometry of the ligand and their investigated complexes. The biological activity was tested against DNA showing that Cd(II), U(VI)O2, Ni(II) and Mn(II) complexes had powerful and complete degradation effect. Also, the ligand and its complexes were screened against Bacillus thuringiensis as Gram-positive bacteria and Pseudomonas aeuroginosa as Gram-negative bacteria using the inhibitory zone diameter.

1,3,7-Trimethyl-2,4-dioxo-1,2,3,4-tetra-hydro-pteridine-6-carboxylic acid hemihydrate

In the title compound, C₁₀H₁₀N₄O₄·0.5H₂O, the two rings of the pteridine system are nearly coplanar [dihedral angle = 4.25 (9)°]. The atoms of the carboxyl group are also coplanar with the pteridine unit [r.m.s. deviation from the mean plane of the pteridine skeleton = 0.092 (2) Å]. In the crystal, the presence of the water molecule of crystallization (O atom site symmetry 2) leads to a hydrogen-bonding pattern different from the one shown by many carboxylic acid compounds (dimers formed through O—H⋯O hydrogen bonds between neighbouring carboxyl groups): in the present structure, the water mol­ecule, which lies on a binary axis, acts as a bridge between two mol­ecules, forming a hydrogen-bonded dimer. In addition to the hydrogen bonds, there are π–π ring stacking inter­actions involving the pyrimidine and pyrazine rings [centroid–centroid distance = 3.689 (1)Å], and two different pyrazine rings [centroid–centroid distance = 3.470 (1)Å]. Finally, there is a C—O⋯π contact involving a carboxyl­ate C—O and the pyrimidine ring with a short O⋯Cg distance of 2.738 (2) Å.

(6-Acetyl-1,3,7-trimethyllumazine-κ3O4,N5,O6)bis(triphenylphosphine-κP)copper(I) hexafluoridophosphate

The title compound, [Cu(C₁₁H₁₂N₄O₃)(C₁₈H₁₅P)₂]PF₆, is the third example reported in the literature of a five-coordinated Cu^IP₂NO₂ system. The metal is coordinated to both PPh₃ mol­ecules through the P atoms and to the pyrazine ring of the lumazine mol­ecule through an N atom in a trigonal–planar arrangement; two additional coordinated O atoms, at Cu—O distances longer than 2.46 Å, complete the coordination. The coordination environment can be described as an inter­mediate square-pyramidal/trigonal–bipyramidal (SP/TBP) polyhedron.

Metal complexes with the ligand derived from 6-acetyl-1,3,7-trimethyllumazine and benzohydrazide. Molecular structures of two new Co(II) and Rh(III) complexes and analysis of in vitro antitumor activity

The structures and spectroscopic properties of new Mn(II), Co(II), Cd(II), Hg(II), Ag(I), Rh(III), and Ir(I) complexes with the ligand BZLMH derived from 6-acetyl-1,3,7-trimethyllumazine (lumazine=pteridine-2,4(1H,3H)-dione) and benzohydrazide are reported. Complexes have been characterized by elemental analyses, spectroscopic studies (IR, UV-vis, (1)H, (13)C and (15)N NMR) and magnetic measurements. In all the complexes, the lumazine-derived ligand appears to be coordinated in either tridentate (N5, N61 and O63) or tetradentate forms (O4, N5, N61 and O63). The molecular structures of the [Co(BZLMH)(H(2)O)(CH(3)CN)(2)](ClO(4))(2) x CH(3)CN and [RhCl(2)(BZLM)(CH(3)CN)] x CH(3)CN complexes, determined by single crystal X-ray diffraction, have allowed to corroborate both coordination behaviours. The cytotoxic activity of the free ligand and complexes against human neuroblastoma NB69 cell line is also described. The differential analysis of the initial cytotoxic screening data has shown good activity only for the [RhCl(2)(BZLM)(CH(3)CN)] x CH(3)CN compound at concentrations at around 2 microM; for the other complexes, a modulation of the cell growth was not found upon complexation, this non-specific effect strongly suggesting an apoptotic behaviour.