Peculiar sandwich-like π–π interaction regulating the nonplanarity of the model heme crystals

X-ray crystallographic analysis of bis(pyridine N-oxide) complexes of iron(III) porphyrinates has revealed that the two pyridine rings of the axial ligands correctly sandwich the porphyrin ring to induce the deformation of commonly observed S₄ saddled porphyrin ring.     

Supramolecular π–π assembly of a neutral [Cu(salen)] complex via the templating effect of an ionic inorganic complex Na2[Cu(mnt)2] forming a framework type material having well-defined channels

A classical ionic inorganic complex Na₂[Cu(mnt)₂] (mnt²⁻ = maleonitriledithiolate = 1,2-dicyanoethylenedithiolate), that acts as a template in assembling neutral [Cu(salen)] (salen = bis(salicylidene)ethylenediamine) complexes forming a framework type arrangement, is accommodated in the channel formed in the crystal structure of a new type of host–guest compound [Cu(salen)]₄ · Na₂[Cu(mnt)₂] (1). The non-covalent supramolecular interactions among [Cu(salen)] complexes and between [Cu(salen)] and [Cu(mnt)₂]²⁻ complexes in the crystal lattice of 1 result in weak antiferromagnetic coupling.     

Monosaccharide Derivatives with Low‐Nanomolar Lectin Affinity and High Selectivity Based on Combined Fluorine–Amide,Phenyl–Arginine,Sulfur–π, and Halogen Bond Interactions

The design of small and high‐affinity lectin inhibitors remains a major challenge because the natural ligand binding sites of lectin are often shallow and have polar character. Herein we report that derivatizing galactose with un‐natural structural elements that form multiple non‐natural lectin–ligand interactions (orthogonal multipolar fluorine–amide, phenyl–arginine, sulfur–π, and halogen bond) can provide inhibitors with extraordinary affinity (low nanomolar) for the model lectin, galectin‐3, which is more than five orders of magnitude higher than the parent galactose; moreover, is selective over other galectins.     

Gold(I)‐Catalyzed Decarboxylation of Propargyl Carbonates: Reactivity Reversal of the Gold Catalyst from π‐Lewis Acidity to σ‐Lewis Acidity

A cationic gold(I)‐catalyzed decarboxylative etherification of propargyl carbonates to selectively produce propargyl ethers is reported. In the reaction the gold(I) catalyst shows a distinct σ‐Lewis acidity rather than the commonly observed π‐Lewis acidity, and thus catalyzes the decarboxylation of a variety of propargyl carbonates to give the corresponding propargyl ethers with high selectivity. This reaction represents a rare example of the tunable reactivity of cationic gold(I) complexes between σ‐Lewis acidity and π‐Lewis acidity.

     

CO2 adsorption and activation over γ-Al2O3-supported transition metal dimers: A density functional study

Catalytic conversion of CO₂ to liquid fuels has the benefit of reducing CO₂ emission. Adsorption and activation of CO₂ on the catalyst surface are key steps of the conversion. Herein, we used density functional theory (DFT) slab calculations to study CO₂ adsorption and activation over the γ-Al₂O₃-supported 3d transition metal dimers (M₂/γ-Al₂O₃, M = Sc–Cu). CO₂ was found to adsorb on M₂/γ-Al₂O₃ negatively charged and in a bent configuration, indicating partial activation of CO₂. Our results showed that both the metal dimer and the γ-Al₂O₃ support contribute to the activation of the adsorbed CO₂. The presence of a metal dimer enhances the interaction of CO₂ with the substrate. Consequently, the adsorption energy of CO₂ on M₂/γ-Al₂O₃ is significantly higher than that on the γ-Al₂O₃ surface without the metal dimer. The decreasing binding strength of CO₂ on M₂/γ-Al₂O₃ as M₂ changes from Sc₂ to Cu₂ was attributed to decreasing electron-donation by the supported metal dimers. Hydroxylation of the support surface reduces the amount of charge transferred to CO₂ for the same metal dimer and weakens the CO₂ chemisorption bonds. Highly dispersed metal particles maintained at a small size are expected to exhibit good activity toward CO₂ adsorption and activation.     

Ionic polymers with expanded π‐conjugation systems derived from through‐space interaction in piperazinium and homopiperazinium rings

Reactions of N‐(2,4‐dinitrophenyl)‐4‐arylpyridinium chlorides (aryl (Ar) = phenyl and 4‐biphenyl) with piperazine or homopiperazine caused opening of the pyridinium ring and yielded polymers that consisted of 5‐piperazinium‐3‐arylpenta‐2,4‐dienylideneammonium chloride (? N(CH₂CH₂)₂N⁺ (Cl^?)?CH? CH?C(Ar)? CH?CH? ) or 5‐homopiperazinium‐3‐arylpenta‐2,4‐dienylideneammonium chloride (? N(CH₂CH₂CH₂)(CH₂CH₂)N⁺ (Cl^?)?CH? CH?C(Ar)? CH?CH? ) units. ¹H NMR spectral analysis suggested that the π‐electrons of the penta‐2,4‐dienylideneammonium group of the polymers were delocalized. UV‐visible spectral measurements revealed that the π‐conjugation system expanded along the polymer chains because of the orbital interaction between electrons of the two nitrogen atoms of the piperazinium and homopiperazinium rings. However, the π‐conjugation length depended on the distance between the two nitrogen atoms; that is, the polymers containing the piperazinium ring had a longer π‐conjugation length than those containing the homopiperazinium ring. Conversion of the piperazinium and homopiperazinium rings from the boat to the chair form led to a decrease in the π‐conjugation length. The surface of pellets that were molded from the polymers exhibited metallic luster, and these polymers underwent electrochemical oxidation in solution. Copyright © 2010 Society of Chemical Industry     

Subsolidus relations in the BaO–La2O3–V2O5 phase diagram

The subsolidus region of the BaO–La₂O₃–V₂O₅ phase diagram has been redetermined. Previously reported binary phases of LaVO₄, La₈V₂O₁₇, La₃VO₇, BaLa₂O₄, Ba₃V₂O₈, Ba₂V₂O₇, Ba₃V₄O₁₃ and BaV₂O₆ have all been confirmed. The ternary phases Ba₂LaV₃O₁₁, Ba₃LaV₃O₁₂ and Ba₃La₄₀V₁₂O₉₃ have also been confirmed. The new phase “BaLa₁₀V₄O₂₆” has been synthesised for the first time and is reported here along with the amended phase diagram. The previously omitted phase of La_1.42V_0.58O_3.58 has also been included and reasons for this are cited. The diagram is shown for two temperatures (1000 and 600 °C) due to the low melting point of V₂O₅-rich compounds.     

Self-assembly of organometallic Pd(II) complexes via CH3π interactions: The first example of a cyclopalladated compound with herringbone stacking pattern

Two binuclear cyclometallated compounds [Pd(C²,N-dmba)(μ-N₃)]₂ (1) and [Pd₂(C²,N-dmba)₂(μ-N₃)(μ-Cl)] (2) (dmba = N,N-dimethylbenzylamine) have been synthesized and characterized by elemental analysis, IR and NMR spectroscopies and single crystal X-ray diffraction crystallography. The ability of CH₃ groups to form C(sp³)Hπ hydrogen bonds with phenyl rings is responsible for the molecular self-assembly within the crystals of 1 and 2. Compound 1 crystallizes as one-dimensional supramolecular chains whereas the crystal packing of 2 consists of a herringbone of sandwiches composed by two inversely related [Pd₂(C²,N-dmba)₂(μ-N₃)(μ-Cl)] molecules.     

The first P–N containing RuCl3NO complex: fac-[RuCl3(NO)(P–N)] (P–N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine)

Complex fac-[RuCl₃(NO)(P–N)] was synthesized from [RuCl₃(H₂O)₂(NO)] in methanol solution under reflux. The orange solid obtained was characterized by NMR (³¹P{¹H}, ¹H, ¹³C) and, cyclic voltammetry, ESI-MS, IR, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} reveals the presence of singlet at 36 ppm. IR N–O stretching as KBr pellets or CH₂Cl₂ solution presented 1866 cm⁻¹ and 1872 cm⁻¹, respectively.     

An ionic liquid‐based polymer with π‐stacked structure as all‐solid‐state electrolyte for efficient dye‐sensitized solar cells

An ionic liquid based polymer, poly(1‐ethyl‐3‐(acryloyloxy)hexylimidazolium iodide) (PEAI), was synthesized and employed as electrolyte to fabricate all‐solid‐state dye‐sensitized solar cells. The photophysical properties of PEAI were studied by UV–vis absorption spectroscopy and photoluminescence spectroscopy. PEAI exhibited significant hypochromism and red shift in UV–vis absorption spectra and large Stokes shifts in photoluminescence spectra, indicating the formation of a novel π‐stacked structure in which the imidazolium rings in the side chain were stacked. Without iodine in its preparation, DSC with PEAI electrolyte achieved a conversion efficiency of 5.29% under AM 1.5 simulated solar light irradiation (100 mW cm^?2). The side‐chain imidazolium π‐π stacking in PEAI played a key role in the holes transport from the photoanode to the counter electrode. Both the open‐circuit voltage and short‐circuit current density showed decreases with the increase in the content of iodine in PEAI electrolyte. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Phosphate triester hydrolysis promoted by S3–zinc(II) complexes with a bridged hydroxide: The crystal structure of TtiZn–OP(O)(OC6H4-p-NO2)2, Tti = hydrotris(N-xylyl-2-thioimidazolyl)borate

The bridged μ-hydroxo dinuclear four-co-ordinated zinc(II) complex 2, derived from hydrotris(N-xylyl-2-thioimidazolyl)borate cleaves the P–O bond in tris(p-nitrophenyl)phosphate to form a mixture of a monomeric phosphate diester complex 3 and phenoxo complex 4.     

Self-assembly through hydrogen-bonding and C–Hπ interactions in metal complexes of N-functionalised glycine

The complex [Ni(L1)₂(py)₂]. toluene (L1 is N-phthaloylglycinato and py is pyridine) was prepared from solid state reaction whereas co-crystals having composition 2[Ni(L1)₂(py)₃(H₂O)] · [Ni(L1)₂(py)₂(H₂O)₂] · 2py · 2H₂O was obtained from solution state reaction.     

High temperature SrCe0.9Eu0.1O3−δ proton conducting membrane reactor for H2 production using the water–gas shift reaction

The water–gas shift (WGS) reaction is used to shift the CO/H₂ ratio prior to Fischer–Tropsch synthesis and/or to increase H₂ yield. A WGS membrane reactor was developed using a mixed protonic–electronic conducting SrCe_0.9Eu_0.1O_3−δ membrane coated on a Ni–SrCeO_3−δ support. The membrane reactor overcomes the thermodynamic equilibrium limitations. A 46% increase in CO conversion and total H₂ yield was achieved at 900 °C under 3% CO and 6% H₂O, resulting in a 92% single pass H₂ production yield and 32% single pass yield of pure permeated H₂.     

Synthesis and characterization of novel star polymer with β‐cyclodextrin core and its metal complexes

A novel star polymer with β‐cyclodextrin (β‐CD) core and polyacrylonitrile arms and its metal complexes (Cu²⁺, Zn²⁺, and Ag⁺) were synthesized and characterized by means of infrared spectra, ultraviolet, GPC, X‐ray photoelectron spectroscopy, differential scanning calorimetry, cyclic voltammetry, and electron spin resonance. The results indicate that the monomers of acrylonitrile were initiated by functionalized β‐CD. The thermal properties of star polymer were improved greatly after transitional metal ions were introduced into it. The novel star polymer metal complexes possess properties of metal ions, polymer, and β‐CD. Furthermore, it shows stable electrochemical activity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Multiple anion···π interactions with a soft selenium atom: Accommodation of NCSe anions inside hydrophobic pockets of adamantane/1,2,4-triazole coordination framework

A new framework coordination polymer {[Cd₃(tr₂ad)₆](NCSe)₆·12H₂O}_n [tr₂ad-4,4′-(adamantane-1,3-diyl)bis(1,2,4-triazole)] exhibits 3D primitive cubic topology adopted by trinuclear [Cd₃(tr)₁₂] net nodes and tridentate tr₂ad links. The structure reveals unprecedented multiple anion ···π interactions employing the soft Se site of the ambifunctional NCSe^? anion and three triazole groups pre-arranged on a tricadmium matrix. The framework generates hydrophobic pockets serving for hosting the uncoordinated anions by a concerted action of Se···π and CH···Se interactions.     

Influence of Ru segregation on the activity of Ru–Co/γ-Al2O3 during FT synthesis: A comparison with that of Ru–Co/SiO2 catalysts

γ-Al₂O₃ and SiO₂ supported Co catalysts, with varying amounts of Ru, were prepared and evaluated for Fischer–Tropsch synthesis (FTS). The composition of Ru for optimum activity was found to be support-dependent. The reducible Co₃O₄ was high in the region of 0–1.64 wt.% of Ru in Co/SiO₂ catalysts. Co/γ-Al₂O₃ displayed a maximum for reducible Co species at 0.42 wt.% Ru. Segregation of Ru occurred beyond this composition decreasing the extent of reduction. Co/γ-Al₂O₃ catalysts showed lower activity and olefin selectivity, in spite of higher Co dispersion, than Co/SiO₂ catalysts. The catalytic performance depends on the amount of reducible Co species, which again depends upon the optimum content of Ru.     

Polyimide–polysiloxane block copolymers synthesized from α, ω-(3-aminophenoxy) terminated poly[oxy(dimethylsilyl)-1,4-phenylene(dimethylsilylene)]s

A method has been worked out for the synthesis of α,ω-(3-aminophenoxy) terminated poly[oxy(dimethylsilyl)-1,4-phenylene(dimethylsilylene)]oligomers with controlled molecular weight. From these oligomers were synthesized polyimide-polysiloxane block copolymers via a transimidization route, with polyimide moieties based on 2-aminopyridine terminated 5,5′-oxybis-1,3-isobenzofuranedione-4,4′-[1,4-phenylenebis(1-methylethylidene)]bisaniline oligomers. The copolymers obtained show higher thermooxidative stability in comparison with copolymers having siloxane moiety based on α,ω-aminopropyl or α,ω-arylamine terminated poly(dimethylsiloxane) oligomers.     

CoMo/MgO–Al2O3 supported catalysts: An alternative approach to prepare HDS catalysts

Three different supports were prepared with distinct magnesia–alumina ratio x = MgO/(MgO + Al₂O₃) = 0.01, 0.1 and 0.5. Synthesized supports were impregnated with Co and Mo salts by the incipient wetness method along with 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) as chelating agent. Catalysts were characterized by BET surface area, Raman spectroscopy, SEM-EDX and HRTEM (STEM) spectroscopy techniques. The catalysts were evaluated for the thiophene hydrodesulfurization reaction and its activity results are discussed in terms of using chelating agent during the preparation of catalyst. A comparison of the activity between uncalcined and calcined catalysts was made and a higher activity was obtained with calcined MgO–Al₂O₃ supported catalysts. Two different MgO containing calcined catalysts were tested at micro-plant with industrial feedstocks of heavy Maya crude oil. The effect of support composition was observed for hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrodenitrogenation (HDN) reactions, which were reported at temperature of 380 °C, pressure of 7 MPa and space-velocity of 1.0 h⁻¹ during 204 h of time-on-stream (TOS).     

Thermodynamic evaluation of the Al2O3–H2O binary system at pressures up to 30 MPa

The behaviour of the hydrated phases in the Al₂O₃–H₂O system is of major importance in the chemistry of ceramic materials. In this work, stability and metastability relations in the Al₂O₃–H₂O system have been studied. Gibbs free energy functions of the gibbsite and boehmite phases have been critically revised and new optimized functions have been calculated. The functions obtained have been used to predict the stability and metastability relations by calculating a P–T diagram following the CALPHAD methodology. Comparison with the corresponding available experimental data is discussed.     

Selective propylene dimerization to 2,3-dimethylbutenes by homogeneous catalysts prepared by oxidative addition of α-nitroketones to nickel(0) complexes in the presence of phosphine ligands and organoaluminium co-catalysts

Novel nickel catalysts, prepared in situ by oxidative addition of α-nitroketones to nickel(0) complexes, in the presence of a phophine ancillary ligand and activated by organoaluminium co-catalysts were investigated in propylene oligomerization with the aim to selectively obtain 2,3-dimethylbutenes (DMB). In particular, the effect of the nature of the α-nitroketonate ligand as well as of the basicity and bulkiness of the phosphine on catalyst performances were studied. Finally, the influence of the type of organoaluminium co-catalyst and reaction temperature were examined.In particular, when the Ni(cod)₂/tricyclohexylphosphine (PCy₃)/α-nitroacetophenone (naph)/methylalumoxane (MAO) catalytic system was employed, the highest up to now reported regioselectivity within C₆ cut (>90%) was achieved. Moreover, the use of balanced mixtures of MAO and Et₂AlCl allowed to optimize the catalyst performances up to an overall yield to DMB of almost 70%, a significant productivity being also achieved (TOF=4500 h⁻¹).