Structural Insights into New Bi(III) Coordination Polymers with Pyridine-2,3-Dicarboxylic Acid: Photoluminescence Properties and Anti-Helicobacter pylori Activity.

Two novel coordination polymers, [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1) and {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2) were prepared using as a prolinker pyridine-2,3-dicarboxylic acid (2,3pydcH2). The obtained complexes were fully characterized by elemental analysis, TG/DTG, FT-IR, solid-state photoluminescence, DFT calculations and single-crystal X-ray diffraction. The obtained complexes crystallized in the triclinic P-1 space group (1) and comprise dimeric units with two crystallographically different Bi(III) centers (polyhedra: distorted pentagonal bipyramid and bicapped trigonal prism) and monoclinic P21/c space group (2) with a distorted monocapped pentagonal bipyramid of Bi(III) center. The various coordination modes of bridging carboxylate ligands are responsible for the formation of 1D chains with 4,5C10 (1) and 2C1 (2) topology. The photoluminescence quantum yield for polymer 2 is 8.36%, which makes it a good candidate for more specific studies towards Bi-based fluorescent materials. Moreover, it was detected that polymer 1 is more than twice as active against H. pylori as polymer 2. It can be concluded that there is an existing relationship between the structure and the antibacterial activity because the presence of chloride and triethylammonium ions in the structure of complex 2 reduces the antibacterial activity.

Theoretical Investigation of Anion-Radical States of Edge-Oxidized Carbon Model Clusters.

A set of flat carbon clusters and ultrashort carbon nanotubes in different anion-radical states was investigated by density functional theory and complete-active space self-consistent field methods. It was found that carbon nanoparticles with pervasively oxidized edges are extremely strong oxidants, and their ground states in catalytic studies should be considered as negatively charged rather than neutral, as it is traditionally done. Negative charging renders initially diamagnetic/semiconducting types of carbon nanoparticles into half-metallic, which can also be achieved by doping with transition metals.

Synthesis and physicochemical characterization of two lead(II) complexes with O-, N-donor ligands. Lone pair functionality and crystal structure.

A dinuclear [Pb2(4-CHO-5-MeIm)6(NO3)2](NO3)2 (1) and a polynuclear [Pb(2-pzc)2(H2O)]n (2) complexes (where 5(4)-carbaldehyde-4(5)-methylimidazole (5(4)-CHO-4(5)-MeIm) and pyrazine-2-carboxylic acid (2-pzcH)) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. Structural determination for complex 1 reveals a cationic species [Pb(4-CHO-5-MeIm)3]2+ connected through bridging nitrate(V) ions. There are also an uncoordinated nitrate ions as counterions. Complex 2 is a three-dimensional architecture consisting of Pb6O12 building units. The pyrazine-2-carboxylato ligand behaves as a chelating agent and a bi-connective bridge. The coordination polyhedra around lead(II) ion could be described as a distorted docecahedron (1) or monocapped trigonal prism (2). The luminescent properties of 1 and 2 investigated in the solid state at room temperature indicate structure-dependent photoluminescent properties. The DFT calculations and the X-ray structural data point on rather hemidirected type of coordination around Pb(II) ions of 1 and 2.

Density functional theory versus complete active space self-consistent field investigation of the half-metallic character of graphite-like and amorphous carbon nanoparticles.

Model carbon nanoparticles representative of the graphite-like and amorphous domains of active carbon are investigated with density functional theory (DFT) and complete active space self-consistent field (CASSCF) methods. Cyclic carbon clusters containing conjugated carbene groups are found to undergo Jahn-Teller distortion. More importantly, the half-metallicity, that is, the equal or similar stability of various spin states, previously suggested by DFT calculations for both types of nanosized clusters is confirmed by CASSCF calculations. Furthermore, the model carbon clusters are found to possess a multiconfigurational electronic structure dominated by high-spin configurations. When compared to CASSCF results, the single-reference DFT predicts proper electronic structures, characterized by antiferromagnetically coupled electron pairs, at the expense of spin contamination as a reflection of the multiconfigurational character. In fact, spin contamination, which is normally viewed as an error, does not corrupt the energetics of the half-metallic systems and therefore does not preclude the applicability of DFT to such systems.

Focused enumeration and assessing the structural diversity of scaffold libraries: conformationally restricted bicyclic secondary diamines.

Comprehensive enumeration of conformationally restricted bicyclic secondary diamines (CRDA) was performed within defined structural limits, yielding a library of all theoretically possible compounds of this class, potentially useful as building blocks for drug design. In order to assess structural diversity of the generated library, molecular geometries of the library members were optimized using DFT calculations. It was shown that the distance between the amino groups and their relative orientation in space vary widely over the whole library, which might be beneficial for diversity-oriented conformational restriction approach in drug discovery. There are many representatives of "three-dimensional" scaffolds in the CRDA library. Selected literature data on biological activity of the known CRDA derivatives were discussed, demonstrating utility of the CRDA scaffold hopping in drug design.

Visible-light photooxidation of water to oxygen at hybrid TiO2 -polyheptazine photoanodes with photodeposited Co-Pi (CoO(x)) cocatalyst.

A cobalt oxide-based oxygen-evolving cocatalyst (Co-Pi) is photodeposited by visible-light irradiation onto nanocrystalline TiO(2)-polyheptazine (TiO(2)-PH) hybrid photoelectrodes in a phosphate buffer. The Co-Pi cocatalyst couples effectively to photoholes generated in the surface polyheptazine layer of the TiO(2)-PH photoanode, as evidenced by complete photooxidation of water to oxygen under visible-light (λ>420 nm) irradiation at moderate bias potentials. In addition, the presence of the cocatalyst also reduces significantly the recombination of photogenerated charges, particularly at low bias potentials, which is ascribed to better photooxidation kinetics resulting in lower accumulation of holes. This suggests that further improvements of photoconversion efficiency can be achieved if more effective catalytic sites for water oxidation are introduced to the surface structure of the hybrid photoanodes.

Reaction of N≡W(O(t)Bu)3 with σ3λ5-phosphoranes. The [2 + 2] cycloaddition across the W≡N triple bond results in the first representative of an inorganic four-membered metallacycle with conjugated endo- and exocyclic double bonds.

The reactions of N≡W(O(t)Bu)(3) with the low-coordinate phosphorus compounds (Me(3)Si)(2)NP(NSiMe(3))(2) (I) and (Me(3)Si)(2)NPS(N(t)Bu) (II) were studied. Quantum chemical calculations were used to determine why Mo- and W-containing compounds with the same composition have different molecular structures.

Visible-light photocurrent response of TiO2-polyheptazine hybrids: evidence for interfacial charge-transfer absorption.

We investigated photoelectrodes based on TiO(2)-polyheptazine hybrid materials. Since both TiO(2) and polyheptazine are extremely chemically stable, these materials are highly promising candidates for fabrication of photoanodes for water photooxidation. The properties of the hybrids were experimentally determined by a careful analysis of optical absorption spectra, luminescence properties and photoelectrochemical measurements, and corroborated by quantum chemical calculations. We provide for the first time clear experimental evidence for the formation of an interfacial charge-transfer complex between polyheptazine (donor) and TiO(2) (acceptor), which is responsible for a significant red shift of absorption and photocurrent response of the hybrid as compared to both of the single components. The direct optical charge transfer from the HOMO of polyheptazine to the conduction band edge of TiO(2) gives rise to an absorption band centered at 2.3 eV (540 nm). The estimated potential of photogenerated holes (+1.7 V vs. NHE, pH 7) allows for photooxidation of water (+0.82 V vs. NHE, pH 7) as evidenced by visible light-driven (λ > 420 nm) evolution of dioxygen on hybrid electrodes modified with IrO(2) nanoparticles as a co-catalyst. The quantum-chemical simulations demonstrate that the TiO(2)-polyheptazine interface is a complex and flexible system energetically favorable for proton-transfer processes required for water oxidation. Apart from water splitting, this type of hybrid materials may also find further applications in a broader research area of solar energy conversion and photo-responsive devices.