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A new azo-ligand, 1,3-dimethyl-5-(p-carboxy-phenylazo)-6-aminouracil (H3L) containing 6-aminouracil (a biomolecule) and a carboxylic function (a potential linker) was synthesized. This ligand was then employed for complexation with Ni(II), resulting in the Ni(II)/Na(I) heterometallic {[NiNa2(μ-HL)2(μ-H2O)2(H2O)6]·6H2O}n (1) and Ni(II) homometallic {[Ni2(μ-HL)2(H2O)4]·5·.5H2O}n (2) 1D coordination polymers. These were obtained from similar reaction mixtures and conditions, except the type of the base (NaOH for 1 or KOH/Et3N for 2). Compounds 1 and 2 were characterized by single-crystal X-ray diffraction, UV-vis, NMR, and IR spectroscopy. Both the coordination polymers 1 and 2 show resembling zigzag chains that are topologically classified as 2-connected underlying nets with the 2C1 topology. In 1, the 1D metal-organic chains are further extended by intermolecular H-bonds, giving rise to a 3D H-bonded net; it is topologically described as a uninodal 6-connected net with the pcu topology. In solution, the 1D polymeric structures of both compounds disaggregate into monomeric Ni(II)-square-planar complex units [Ni(HL)2]2−, as evidenced by NMR and UV-vis spectroscopy studies. The magnetic properties of 2 were also investigated, indicating a dominant zero field splitting parameter D of the Ni(II) center. The type of the base is important for tuning the selective formation of the desired product 1 or 2. Density functional theory (DFT) study justifies the experimental findings for a base-assisted selectivity between the compounds 1 or 2 by optimizing their structures at the PBE-D/DNP level of theory. The existence of agostic interactions between the C–H bonds of the methyl groups of the coordinated HL2− moieties and the Ni centers in both structures is suggested by natural bond orbital (NBO) calculations at the M06-2X/6-31 + G∗ level of theory. The compound 1 proves to be a potential inhibitor of a bacterial virulence factor, pyocyanin. © 2018 Elsevier B.V.

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Inorganica Chimica Acta

Nickel(II) based homo- vs heterometallic 1D coordination polymers derived from a novel 6-aminouracil building block: Structures, topologies, non-covalent interactions, magnetism, and antibacterial activity

Crystalline copper Schiff base complexes of general formula [CuL1NO3]n (1) and [CuL2Cl] (2) (where HL1 = 1-[(3-dimethylaminopropylimino)-methyl]-naphthalen-2-ol and HL2 = 3-[(3-dimethylamino-2,2-dimethyl-propylimino)-methyl]-naphthalen-2-ol) were prepared and well characterized. The guest, metal complexes were entrapped in the supercages of NaY zeolite (host) in the solvent phase through two stage process (i) ion exchange of the selected transition metal (Cu(II)-salt) in the porous structure and (ii) encapsulation of Schiff-base ligands (HL1/HL2) in Cu(II) exchanged zeolite. The novel Cu(II) complexes as well as host-guest catalysts were characterized using various physicochemical [Single crystal XRD, elemental analysis, EDX, scanning electron microscopy (FE-SEM), the Brunauer-Emmet-Teller (BET) adsorption technique (N2 gas), Inductively coupled plasma (ICP-MS), powder X-ray diffraction (PXRD), thermal analysis (TGA), cyclic voltametry] and spectroscopic techniques [1H and 13C NMR, FT-IR, ESI-MS, electro spin resonance (ESR), diffuse reflectance spectroscopy (DRS), FT-Raman and GC-MS]. Herein, this study reveals the advantage of heterogeneous catalytic methods for the stability of metal complexes into the supercages of zeolite-Y and the selective oxidation of phenol, styrene and cyclohexene in presence of H2O2 at mild reaction conditions. The catalytic activities of the zeolite entrapped Cu(II) complexes were tested with their homogeneous analogous as well. The heterogeneous catalyst can be re-used after recovering for several cycles without decay of activity which was confirmed by PXRD, cyclic voltammetry, SEM and FTIR studies. © 2018 Elsevier Inc.

Microporous and Mesoporous Materials

Zeolite encapsulated host-guest Cu(II) Schiff base complexes: Superior activity towards oxidation reactions over homogenous catalytic systems

We describe the synthesis of the ruthenacyclic carbamoyl complexes [Ru(2-NHC(O)C5H3NMe)(CO)2(o,o-Me2-C6H3S)(L)] (L = H2O or MeCN), which have a labile water or acetonitrile ligand at their sixth coordination sites. Steric bulk around the ruthenium center is essential in preventing isomerization and dimerization, and embedding within papain can be achieved via coordination of its sole free cysteine residue. The observed chemistry parallels that of the natural [Fe]-hydrogenase. Copyright © 2018 American Chemical Society.

Fulltext

Inorganic Chemistry

Embedding a Ruthenium-Based Structural Mimic of the [Fe]-Hydrogenase Cofactor into Papain

In this research paper we report synthesis of two planar ligands, namely 1,3-dimethyl-5-(4ʹ/3ʹ-pyridylazo)-6-aminouracil: HL1 (1) for 4ʹ-pyridyazo- and HL2 (2) for 3ʹ-pyridyazo-group and, moreover, their nickel (II) square planar complexes ([NiII(L1)2] (3) and ([NiII(L2)2] (4)). The report is also included solid and solution state structure of the compounds and study of noncovalent stacking interactions. Crystal structures of the ligands, 1 and 2 are monoclinic with alike space group P21/c and the complex 3 is also monoclinic with space group C2/c. The molecular electrostatic potential (MEP) analysis shows that the ligands possess both π-basic and π-acid character in the same framework over the center of the pyridine and the pyrimidine rings, respectively, favoring electrostatically enhanced π-π stacking interaction among the molecular units. Upon complexation, π-acidity of the pyrimidine ring increases, and the complex 3 exhibits lone pair (lp)-π stacking interaction involving lone pair of the pyridine N-atom and π-acid pyrimidine plane. The study evidences that the ligands exist in azo-enamine-keto tautomer in solid and hydrazone-imine-keto in solution state and get coordinated with nickel (II) via azo-N and uracil-6-NH– to form a distorted square planar complex. Electronic absorption bands/energies obtained from experimental and theoretical (TDDFT) study are indeed alike, giving reliability to the level of theory and the absorption band assignments. Moreover, the synthesized compounds containing uracil and pyridine fragments exhibit π-π/lp-π interactions with considerable energy for stabilization of their assemblies in the solid state. © 2018 Elsevier B.V.

Journal of Molecular Structure

Synthesis, structures, and investigation of noncovalent interactions of 1,3-dimethyl-5-(4ʹ/3ʹ-pyridylazo)-6-aminouracil and their Ni(II) complexes

Two new Cu(II) complexes [Cu(HL)(MeOH)(Py)](ClO4)2 (1), [Cu(HL)(DMF])(NO3)2 (2) have been synthesized from Schiff base ligand [HL = 2-(phenyl((2-(piperazin-1-yl)ethyl)imino)methyl)phenol ] with flexible piperazinyl moiety. Structural analysis reveals that 1 and 2 are monomeric Cu(II) complex consisting of penta and tetra coordinated Cu(II) centers, respectively. Screening tests were conducted to quantify the binding ability of complexes (1 and 2) towards BSA and DNA as well as the protease and nuclease activity of these complexes using gel electrophoresis technique. Furthermore enzyme kinetic studies were also performed for those two complexes towards effectiveness in mimicking catecholase like activities. Overall all the experimental results reveal the potential activity of these copper complexes towards protease, nuclease and catecholase activity. Apart from these, MTT assay was also utilized to scrutinize the anti-proliferative activity which was further investigated using dual staining confocal microscopic images. © 2017 Elsevier B.V.

Investigation on chemical protease, nuclease and catecholase activity of two copper complexes with flexidentate Schiff base ligands

Mechanochemistry has been established to be an environmentally-friendly way of conducting reactions in a solvent-free manner. The development of mechanochemical orthogonal reactions, in which multiple reagents are milled together, can be a powerful strategy to selectively yield the desired product. Such orthogonal syntheses are rare, especially those involving main group frameworks-based on bonds other than carbon-which are yet to be reported. Herein, we demonstrate the direct formation of air- and moisture-stable cyclophosph(v)azanes enabled by an orthogonal "one-step one-pot" mechanochemical reaction. In addition, detailed hydrolytic- and air-stability studies, conducted over one and 12 months, respectively, revealed high robustness of these compounds. © 2018 The Royal Society of Chemistry.

Chemical Communications

Orthogonality in main group compounds: A direct one-step synthesis of air- and moisture-stable cyclophosphazanes by mechanochemistry

One-electron oxidation of 1,4,2,5-diazadiborinine 1 has been studied. While the reaction of 1 a bearing phenyl groups on the B atoms with AgAl{OC(CF3)3}4 afforded a complex mixture, the same oxidation reaction with 1 b featuring bulky mesityl substituents on the B atoms rendered the corresponding cation radical 2 b as an isolable species. X-ray diffraction analysis, EPR spectroscopy, and DFT calculations of 2 b revealed the delocalization of the unpaired electron over the entire π-system of 2 b, as well as a large spin density (0.76 in total) on the two equivalent boron atoms. The chemical trapping reaction of 2 b with p-benzoquinone and triphenyltin hydride afforded the dicationic species 3 containing two newly formed B−O bonds and the monocationic product 2b-H containing a B−H bond, respectively, thus confirming the boron-centered radical reactivity of 2 b. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Angewandte Chemie - International Edition

A Crystalline Diazadiborinine Radical Cation and Its Boron-Centered Radical Reactivity

The coordination chemistry of an amidinato silylene and germylene toward group 14 element(ii) halides is described. The reaction of the amidinato silicon(ii) amide [LSiN(SiMe3)2] (1, L = PhC(NtBu)2) with SnCl2 and PbBr2 afforded the amidinato silylene-dichlorostannylene and-dibromoplumbylene adducts [L{(Me3Si)2N}SiEX2] (E = Sn, X = Cl (2); E = Pb, X = Br (3)), respectively, in which there is a lone pair of electrons on the Sn(ii) and Pb(ii) atoms. X-ray crystallography, NMR spectroscopy and theoretical studies show conclusively that the Si(ii)-E(ii) bonds are donor-acceptor interactions. Similar electronic structures were found in the amidinato germylene-dichlorogermylene and-dichlorostannylene adducts [L{(Me3Si)2N}GeECl2] (E = Ge (5), Sn (6)), which were prepared by treatment of the amidinato germanium(ii) amide [LGeN(SiMe3)2] (4) with GeCl2·dioxane and SnCl2, respectively. © The Royal Society of Chemistry.

Dalton Transactions

Reactivity of an amidinato silylene and germylene toward germanium(ii), tin(ii) and lead(ii) halides

Several Al-based complexes supported by a bis(imino)aryl NCN pincer ligand have been prepared. Systematic structural and experimental evidence identified a cationic species, supported by a THF molecule, as the best Lewis acid precatalyst for a range of Diels-Alder cycloadditions. This highlighted the importance of fully isolating and characterizing the active species in any catalytic process especially when Lewis acids are used due to the presence of hidden Brønsted acids (HBAs). Finally, the control experiments conducted in order to eliminate HBA activity that involve a bulky pyridine base should be performed with caution as the corresponding protonated pyridinium salt could also serve as a proton source. © The Royal Society of Chemistry.

Pursuing the active species in an aluminium-based Lewis acid system for catalytic Diels-Alder cycloadditions

Here, we present our recent progress on the synthesis, crystal structure, physical properties and DFT calculations of a novel large pyrene-fused N-heteroacene (15RINGS) with 15 aromatic six-membered rings linearly fused in one row. The long conjugated backbone (more than 35 angstrom) of 15RINGS possesses a dual-bending feature (the bending angle is about 13.2 degrees).