The dinuclear phenylboronic ester derived from pentaerythritol and trinuclear triphenylboroxine were combined with three diamine tectons, that is, 1,4‐diazacyclohexane (pz), trans‐1,4‐diaminocyclohexane (1,4‐chda), and 4‐aminopyridine (4‐apy), to generate supramolecular N→B bound assemblies and to enhance the knowledge concerning the factors governing the formation of such aggregates. From these reactions, three novel complexes of composition {(PhBO)3(pz)}n·nDMF (2), {[(PhBO)3]2(1,4‐chda)}·1,4‐chda (3), and {[(PhBO2)2(C5H8)][4‐apy]2}·CHCl3·1.25H2O (4) were achieved and characterized by elemental analysis, IR and NMR spectroscopy, and single‐crystal X‐ray diffraction analysis. Structural characterization in the solid state revealed that all three products exhibit N→B bonds but have different compositions concerning the B and N tectons to give a 1:1 adduct for 2, a 2:1 adduct for 3, and a 1:2 adduct for 4. In the solid state, compound 2 comprises a 1D coordination polymer, whereas compounds 3 and 4 have discrete molecular structures. Owing to the presence of N–H hydrogen‐bonding sites, in all cases overall 2D or 3D hydrogen‐bonding networks are formed. In solution, the N→B aggregates are mostly dissociated at room temperature, as shown by 11B NMR spectroscopy.
Four secondary diamines with aromatic spacer groups derived from α,α′-dibromo-p-xylene and 4,4′-bis(chloromethyl)-1,1′-biphenyl have been transformed into bis-dithiocarbamate ligands and each combined with dimethyl-, di-nbutyl-, and diphenyltin(IV) dichloride to yield a total of 12 mononuclear diorganotin(IV) bis-dithiocarbamate complexes with six-coordinate metal coordination geometries and either 23-or 27-membered macrocyclic structures. The products were fully characterized by IR and NMR ( 1 H, 13 C, 119 Sn) spectroscopy and high-resolution ESI + -TOF mass spectrometry. A representative selection of the macrocyclic complexes was further examined by DFT computational studies and the relative binding [a] 3429 Scheme 1. Synthesis of the macrocyclic diorganotin(IV) bis-dithiocarbamates 1-12. The numbering scheme for the assignment of the NMR spectroscopic data is included.
3431Scheme 3. Illustration of the stereochemical differences found in the molecular structures of the four trans conformers that were geometry-optimized by DFT quantum chemical calculations by using the B3LYP/def2-TZVP method for the dimethyltin complex 1.
3432In all the structures, the Sn-S cov bonds point towards the interior of the macrocycle cavity. The organic groups attached to
Eur.Titration Experiments: For the titration experiments, the receptor was employed at fixed concentrations of 1 × 10 -5 M for 3, 4, 6, and 9 and 2 × 10 -5 M for 12 using chloroform as the solvent. 0.1 M (0.2 M for 12) stock solutions of the anions were prepared in the same solvent from the corresponding tetramethyl ammonium salts. Spectral changes were observed at λ = 300-302 nm and the spectrometric titration curves were analyzed and fitted on the basis of a 1:1 host-guest complexation model using Equation (1) and the Microcal Origin 8.0 program. [23] DFT Calculations: DFT quantum chemical calculations were performed with the quantum mechanical program Gaussian 09 (version B.01) [27] using the B3LYP hybrid functional [28] in combination with the def2-TZVP basis set. [29] Geometry optimizations were realized for different starting geometries of the molecular structures, which were established by molecular modelling considering variations in the metal coordination environment (cis and trans coordina-
Within the current challenges in medicinal chemistry, the development of new and better therapeutic agents effective against infectious diseases produced by bacteria, fungi, viruses, and parasites stands out. With chemotherapy as one of the main strategies against these diseases focusing on the administration of organic and inorganic drugs, the latter is generally based on the synergistic effect produced by the formation of metal complexes with biologically active organic compounds. In this sense, Schiff bases (SBs) represent and ideal ligand scaffold since they have demonstrated a broad spectrum of antitumor, antiviral, antimicrobial, and anti-inflammatory activities, among others. In addition, SBs are synthesized in an easy manner from one-step condensation reactions, being thus suitable for facile structural modifications, having the imine group as a coordination point found in most of their metal complexes, and promoting chelation when other donor atoms are three, four, or five bonds apart. However, despite the wide variety of metal complexes found in the literature using this type of ligands, only a handful of them include on their structures tridentate SBs ligands and their biological evaluation has been explored. Hence, this review summarizes the most important antimicrobial activity results reported this far for pincer-type complexes (main group and d-block) derived from SBs tridentate ligands.
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