A new POM-templated metal–organic complex based on the flexible bis-pyridyl-bis-amide ligand

A new POM-templated metal?Corganic complex [Cu₄(L)₇(H₂O)₁₂(SiMo₁₂O₄₀)₂]·7H₂O [L?=?N,N??-bis(3-pyridinecarboxamide)-1,6-hexane], has been hydrothermally synthesized and characterized by elemental analysis, IR, TG and single-crystal X-ray diffraction analysis. The results reveal that the complex is a 2D metal?Corganic coordination framework of [Cu₄(L)₇(H₂O)₁₂] _n ⁸ⁿ⁺ cations containing decanuclear cycles with dimensions of ca. 17.55?×?57.42 ?, in which the SiMo₁₂O₄₀ ^4? anions act as non-coordinated anionic templates. The electrochemical properties of a bulk-modified carbon paste electrode of the complex have been investigated, and the results indicate that the complex-modified CPE has good electrocatalytic activity toward the reduction of nitrite in aqueous 1?M H₂SO₄ solution.     

A new fluorescent chemosensor for iron(III) based on the β-aminobisulfonate receptor

A simple fluorescent sensor 1 has been developed for the determination of Fe(III) in 100% aqueous solution at pH 7.0. The sensor comprises a novel aminobisulfonate receptor joined to a naphthalene fluorophore via a methylene spacer in the fluorophore-spacer-receptor format of photoinduced electron transfer (PET) based sensors. The fluorescence emission of the sensor was quenched upon addition of Fe(III) ions, most likely due to electron/energy transfer between Fe(III) and the excited naphthalene. The sensor displayed good selectivity for Fe(III) over other physiologically relevant metal ions and can estimate Fe(III) concentration between 16 and 63 μM. Stern Volmer analysis showed the binding stoichiometry to be 1:1 (host-guest) with a binding constant, calculated using the Benesi-Hilderbrand equation, of (7.6 ± 0.6) × 10⁴ M⁻¹.     

Synthesis and luminescence properties of Eu(III)-doped silica nanorods based on the sol–gel process

Uniform Eu³⁺-doped SiO₂ nanorods were synthesized through a simple sol–gel method using cetyltrimethylammonium bromide (CTAB) as surfactant template and tetraethylorthosilicate as silicon source. X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrum, scanning electron microscope (SEM), transmission electron microscopy, and photoluminescence spectra were employed to characterize the products in detail. The nanorods have good uniformity and their diameters and lengths are in the range of 200–300 and 500–700 nm through the SEM images, respectively. The formation of the nanorods was studied by taking SEM images after different aging time. The experimental results indicate that CTAB plays a crucial role in the formation of the silica nanorods. The luminescence of Eu³⁺-doped SiO₂ nanorods is dominated by red-emission around 612 nm due to intra-atomic 4f → 4f (⁵D₀ → ⁷F₂₎ transition of Eu³⁺ ions. Furthermore, the effect of doping concentrations of Eu³⁺ ions on the luminescence was investigated.     

New luminescent heteronuclear Ln(III)–Bi(III) complexes (Ln = Nd,Eu, Tb,Yb) based on aminopolycarboxylic acids

New heteronuclear Ln(III)–Bi(III) complexes (Ln?=?Nd, Eu, Tb, Yb, Lu) with ethylenediamine-N,N,N′,N′-tetraacetic (H₄edta), trans-1,2-cyclohexane-diamine-N,N,N′,N′-tetraacetic (H₄cdta), diethylenetriamine-N,N,N′,N″,N″-pentaacetic (H₅dtpa), and triethylenetetraamine-N,N,N′,N″,N″′,N″′-hexaacetic (H₆ttha) acids have been synthesized with a different synthetic approach. Bi(III) is a sensitizer of the 4f-luminescence in visible and near IR region. Emission spectra of Eu(III)–Bi(III) complexes were studied and the asymmetry of Eu(III) coordination environment was estimated, in good agreement with molecular models. The complexes synthesized by self-assembly are characterized by higher values of the 4f-luminescence quantum yield than other Ln(III)–Bi(III) complexes.     

A novel thiocyanate-selective electrode based on a zinc–phthalocyanine complex

A novel thiocyanate (SCN⁻)-selective PVC membrane electrode based on a zinc-phthalocyanine (ZnPc) complex as neutral carrier is described. The membrane electrode containing ZnPc with 5.1% (w/w) ionophore, 29.2% (w/w) PVC, and 65.7% (w/w) 2-nitrophenyl octyl ether (o-NPOE) as plasticizer displayed an anti-Hofmeister selectivity sequence , and exhibited near-Nernstian potential response to thiocyanate ranging from about 1.0×10⁻¹ to 1.0×10⁻⁶ mol L⁻¹ with a detection limit of 7.5×10⁻⁷ mol L⁻¹ and a slope of 58.1±0.5 mV per decade in pH 3.0 phosphate buffer solution at 25 °C. This preferential response is believed to be associated with the unique coordination between the central metal of the carrier and thiocyanate.      

A new organic–inorganic hybrid based on Mn–salen and decavanadate

An organic–inorganic hybrid based on Mn-salen and decavanadate, [NH₄]₂[Mn(salen)(H₂O)₂]₄[V₁₀O₂₈]?·?6H₂O (1) (salen?=?N,N′-ethylene-bis(salicylideneiminate)), has been synthesized by the strategy of secondary building units in mixed methanol–water solution and was structurally characterized by single-crystal X-ray diffraction, elemental analyses, IR, and UV-Vis. The [Mn(salen)(H₂O)₂]⁺ cations and water molecules are located in the interspaces among the polyoxoanions [V₁₀O₂₈]^6? forming a POM-based supramolecule. Compound 1 is the first example of metal-Schiff-base polyoxovanadates. The photocatalytic analysis, cyclic voltammetry, and electrocatalytic analysis of 1 have been investigated.     

A new P-heterocyclic type of phosphonium–iodonium ylides based on dibenzophosphole

A novel mixed phosphonium–iodonium ylide was synthesized by alkylation of 5-phenyl-5H-dibenzophosphole with phenacyl bromide followed by deprotonation and oxidation of the resulting phosphonium ylide with (diacetoxyiodo)- benzene. The influence of the cyclic nature of the phosphonium moiety on the dynamic E/Z isomerism in the mixed ylide is discussed.     

A new Kagomé lattice coordination polymer based on bismuth and pyridine-2,5-dicarboxylate: structure and photoluminescent properties

A new Kagomé lattice topology assembled from ML(4) metal-organic polyhedra prepared using bismuth nitrate and pyridine-2,5-dicarboxylate has been obtained via a solvo-thermal reaction. Bi(pydc)(2)·(H(3)O(+))(H(2)O)(0.83) is, to the best of our knowledge, the first example of a bismuth-based coordination polymer to form with a Kagomé topology. Its structure and photoluminescence properties are reported.     

Heterogeneous asymmetric Diels–Alder reactions using a copper–chiral bis(oxazoline) complex immobilized on mesoporous silica

A chiral bis(oxazoline)–copper complex was immobilized onto mesoporous silica and the resulting heterogeneous catalyst was employed in asymmetric Diels–Alder reactions. Reactions using the catalyst exhibited good enantioselectivity of 78% enantiomeric excess and endo/exo-selectivity (17:1) better than the corresponding homogeneous reaction. The catalyst could be easily recovered and reused several times without significant loss of the remarkable reactivity, diastereoselectivity and enantioselectivity.     

Crystallization of inorganic silica based on interaction between polyimide and silica by sol–gel method

Crystalline silica in cristobalite phase was successfully prepared at a relatively low temperature of 800 °C by calcinating polyimide/silica hybrid films under ambient air. X-ray photoelectron spectroscopy measurements show that the product is silica after calcination. It is found that the crystallinity is dependent on the removing rate and the strength of the interaction between polyimide and silica. The presence of polyimide plays an important role in the growth of silica. Calcination to remove polyimide with rapid heating results in lower crystallinity compared with calcination with slow heating. For samples with the same content of silica, the crystallinity changes with the strength of the interaction between polyimide and silica molecules.     

Visible light photocatalysis by a Titania–Rhodium(III) complex

Titania hybrid photocatalysts containing 0.5, 1.0, 2.0, and 5.0 wt% of rhodium(III) were prepared by chemisorption of RhCl₃ × 3H₂O onto anatase hydrate powder (TH). Analytical data suggest that a titania–trichlororhodate complex is produced containing a [TiO₂]–O–Rh bond.Similar results are found in the case of modification by RhBr₃ × 3H₂O. Diffuse reflectance spectra exhibit an absorption shoulder throughout the visible region down to 700 nm. Photoelectrochemical measurements indicate that the quasi-Fermi level of electrons is gradually shifted to more anodic potentials with increasing rhodium loading reaching a value of ?0.34 V at pH 7 (vs. NHE) in the case of 5.0%RhCl₃/TH. This is more anodic by 210 mV as compared to unmodified TH. Upon visible light irradiation this photocatalyst induces a fast mineralization of 4-chlorophenol whereas cyanuric acid, which is known to be mineralized in the presence of the analogous Pt(IV) modified titania, is not degraded.     

Copper(II)–lanthanide(III) 15-metallacrown-5 complexes based on pyrazinohydroxamic acid as new multiple-binding pentagonal platforms with Lewis amphoteric nature

Reaction of copper(II) acetate, lanthanium(III) or gadolinium(III) nitrate (1/5 equiv.) with pyrazinohydroxamic acid (H₂Pyzha) in DMF led to a series of new heterobimetallic 15-metallacrown-5 complexes. In a MeOH/H₂O solution the complexes exist as molecular unassociated metallacrowns. In solid state their structures are more complicated as it has been confirmed by X-ray analysis: discrete molecular metallacrowns [Gd(NO₃)₂{Cu(pyzha)}₅(DMF)₄(NO₃)] · 0.5C₆H₆ · H₂O (1), [Gd(NO₃)₂{Cu(pyzha)}₅(DMF)₅](NO₃) · 1.5DMF · 0.5H₂O (2), [La(NO₃)₂{Cu(pyzha)}₅(DMF)₅]NO₃ · 1.5DMF · 2C₆H₆ (3) are solvates, whereas compound [{La(NO₃)₂{Cu(pyzha)}₅(DMF)₅}₂(μ²-NO₃)](NO₃) · 3DMF (4) is a dimer, where μ-bridged nitrate links two copper centres of the adjacent metallamacrocycles. Complex [Gd(NO₃)₂{Cu(pyzha)}₅(DMF)₂(H₂O)(NO₃)] · CH₂Cl₂ · DMF (5) self-associates into a polymer chain by means of one pyrazine moiety and the copper ring atom. Reaction of the molecular metallacrowns with excess of inorganic salts CdBr₂ or Cu(OAc)₂ proceeds as anion methathesis process affording heteroanionic metallacrowns: molecular [Gd(NO₃)₂{Cu(pyzha)}₅(DMF)₅] [Gd(NO₃)₂{Cu(pyzha)}₅(DMF)₄(H₂O)][CdBr₄] · 1.5DMF (6), and 3D hydrogen bonded polymer [La(μ²-OAc)(H₂O)₃{Cu(pyzha)}₅ (H₂O)₄(NO₃)](NO₃) · 4H₂O (7).     

First-principles studies on the efficient photoluminescent iridium(III) complexes with C^N═N ligands

The electronic structures and photophysical properties of several homoleptic iridium complexes IrL(3) with C^N═N ligands, including 1 (L = 3,6-diphenylpyridazine), 2 (L = 1,4-diphenylphthalazine), 3 (L = 3-phenyl-5H-indeno[1,2-c]pyridazine), and 4 (L = 3-phenylbenzo[h]cinnoline), are investigated using the density functional method. The comparison between the calculated results of the four complexes shows that the assumed complex 4 may possess higher photoluminescent quantum efficiency than complexes 1-3 and is the potential candidate to be an efficient green-emitting material. The photophysical properties of the assumed complex 3 can be comparable to that of experimentally found complex 1. For 1 and 3, the emission energies are nearly the same, consistent with their similar HOMO-LUMO energy gaps. Their emission characters are also similar and mainly dominated by one ligand. For 4 and the experimentally found complex 2, although they have similar HOMO-LUMO energy gaps, and their luminescent nature is nearly the same and dominated by the three ligands, the emission spectrum of 4 is blue-shifted as compared to that of 2.     

Dispersion of polymeric-coated–silica aerogel particles in unsaturated polyester composites: Effects on thermal-mechanical properties

The thermal-mechanical properties of unsaturated polyester (UP) composite were enhanced by the dispersion of silica aerogel (SA) with preserved pores. Low-cost SA was prepared from rice husk via the sol-gel process and ambient pressure drying. A new method was proposed to encapsulate the hydrophobic aerogel surface pores with hydrophilic polyvinyl alcohol (PVA) film using the fluidized-bed coating process. The dispersion of PVA-coated aerogel with preserved pores in the polyester matrix resulted in an increase of specific compressive strength (44.1?MPa?·?cm³?g^?1), thermal insulation (0.23?W?m^?1?K^?1), and thermal stability (T_onset?=?310°C), but decreased the glass transition temperature (T_g?=?260°C).     

Features of sol–gel synthesis of new functional materials based on complex oxides with tunnel structure

A new method of sol–gel synthesis has been proposed for fabrication of functional materials with ramsdellite and hollandite types of crystal structure in the following oxide systems: Me₂O–Me′₂O₃–Me″O₂ (Me = Li, K; Me′ = Ga, Cr, Fe, In; Me″ = Ti, Sn). The formation of titanates with ramsdellite-type structure is shown to achieve at the temperature range of 250–650 °C, when gel combustion occurs. This allows fabrication of materials with high specific surface area. The ramsdellite phases and stannate hollandites are shown to form in the temperature range of 1,100–1,150 °C. Thus our method gives the possibility to reduce the thermo-temporal parameters of synthesis for this class of materials.     

A new controlled release system of chlorhexidine and chlorhexidine:βcd inclusion compounds based on porous silica

The purpose of this study was to prepare and characterize a controlled release system based on porous silica loaded with chlorhexidine (Cx) and its inclusion compounds in β-cyclodextrin (βcd), and to evaluate its antimicrobial activity. Acetate chlorhexidine (CxA), gluconate chlorhexidine (CxG), βcd:chlorhexidine acetate 2:1 (βcd:CxA) and βcd:chlorhexidine gluconate 2:1 (βcd:CxG) were incorporated into porous silica. Drug loading was characterized by FTIR, powder X-ray diffraction, thermal analysis and BET, and was shown to be in an amorphous state and porous matrix. The kinetics release parameter of the drug was established, which showed that the Cx systems release profile followed zero order release until 400 h and Higuchi model release until 750 h, after the burst effect at the first 8 h. Chlorhexidine therapeutic range was reached near first hour for all systems. The chlorhexidine porous silica system was biologically active against Enterococcus faecalis and Candida albicans in vitro. The systems showed an efficient Cx controlled release modulated by the presence of the β-cyclodextrin and by the porous silica matrices, providing effective antimicrobial activity.