Modification of faujasites to generate novel hosts for “ship-in-a-bottle” complexes

Zeolites X, Y, and DAY have been modified by a post-synthetical dealumination procedure to generate mesopores that are completely surrounded by micropores. In these novel host materials several bulky transition metal salen complexes have been occluded via the “ship-in-a-bottle” synthesis approach. Both the host materials and the “ship-in-a-bottle” catalysts have been characterized by FTIR spectroscopy and nitrogen adsorption. Additionally, the “ship-in-a-bottle” catalysts have been characterized by thermogravimetric analysis and ICP-AES spectroscopy. The catalysts have been tested in the stereoselective epoxidation of R-(+)-limonene and (−)--pinene with molecular oxygen as oxidant. The best results so far — 100% conversion, 96% selectivity and 91% de — were achieved with the immobilized (R,R)-(N,N′)-bis(3,5-di-tert-butylsalicylidene)-1,2-diphenylethylene-1,2-diaminocobalt complex in the epoxidation of (−)--pinene.     

Microporous coordination polymers of cobalt(II) and manganese(II) 2,6-naphthalenedicarboxylate: preparations, structures and gas sorptive and magnetic properties

Two isostructural coordination polymers M₃(NDC)₃(DMF)₄ (M = Co (1), Mn (2); H₂NDC = 2,6-naphthalenedicarboxylic acid; DMF = N,N′-dimethylformamide) were prepared through conventional and microwave-assisted solvothermal methods. Single crystal X-ray analysis indicated that both complexes crystallized in the monoclinic system with space group C2/c. Powder X-ray diffraction (PXRD) patterns of the bulk samples for the two complexes obtained from microwave-assisted solvothermal syntheses matched well with the simulated ones from the single crystal data as well as the ones prepared by conventional solvothermal method. These microporous cobalt(II) and manganese(II) coordination polymers undergo reversible structural change upon desolvating, giving stable microporous frameworks containing unsaturated metal sites, and resolvating. The desolvated complexes showed different nitrogen gas adsorption capabilities but very close hydrogen adsorption behaviors. Variable-temperature magnetic susceptibilities of 1 and 2 revealed the weak antiferromagnetic coupling between the adjacent metal ions bridged by carboxylate.     

Les proprietes electrochimiques des diphenylamines et de leurs produits d''oxydation en milieu organique—IV. Les diphenylamines p. monosubstituées et les mecanismes de formation des produits de couplage issus des diverses diphenylamines

Anodic processes of p. monosubstituted diphenylamines in acetonitrile medium are studied by rotating disk electrode voltammetry, cyclic voltammetry and controlled potential electrolysis performed with a simultaneous record of visible absorption and esr spectra. Depending upon the acido-basicity of the medium, the primary cation radical gives one or two of the following coupling products: N,N′-diarylbenzidine, 5,10-diaryl 5,10-dihydrophenazine, N,N,N′-triaryl p. phenylenediamine or tetraarylhydrazine. The last two compounds are only observed in basic media. The N,N′-diarylbenzidine results from the C_p—C_p coupling of two radicals Ar₂NH^√+ whereas the tetraarhylhydrazine comes from the dimerization of two radicals Ar₂N^√ in basic media. The dihydrophenazine and the phenylenediamine probably result from the C_p—N coupling between Ar₂NH and the corresponding Ar₂N⁺ ion. The anodic behaviour of various substituted diphenylamines allows the presentation of selection rules for the formation of dihydrophenazines.     

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).     

Thermal graft copolymerization of 4-vinyl pyridine on polyimide to improve adhesion to copper

The surface of poly[N,N′-(oxydiphenylene)pyromellitimide] film, Kapton^® HN, was modified to improve its adhesion to copper metal. The polyimide surface was argon plasma activated and then exposed to air. A nitrogen-containing monomer, 4-vinyl pyridine, was then polymerized at elevated temperature under constant pressure between the argon plasma activated polyimide film and copper foil without any added photoinitiator. Optimization of the argon pretreatment time, curing temperature and curing duration resulted in almost doubling of the single lap shear strength. It is postulated that failure occurred mainly between the polyimide and the poly(4-vinyl pyridine).     

Catalytic oxidation of olefins with hydrogen peroxide catalyzed by [Fe(III)(salen)Cl] complex covalently linked to polyoxometalate

The catalytic activity of a hybrid compound [Fe(salen)-POM] (1) consisting of Fe(III)(salen)Cl [H₂salen = N,N′-bis(salicylidene)ethylenediamine] complex covalently linked to a Keggin type polyoxometalate, K₈SiW₁₁O₃₉, (POM) was studied in the oxidation of various olefins in acetonitrile, using hydrogen peroxide as oxygen source. While, [Fe(salen)-POM] catalyst showed moderate to good catalytic activity and product selectivity in the oxidation reactions, the complex Fe(III)(salen)Cl showed poor catalytic activity in these reactions. The effect of other parameters such solvent, oxidant, temperature and the metal type in Schiff base complex were also investigated.     

Ion-exchange voltammetry of tris(2,2′-bipyridine) nickel(II), cobalt(II), and Co(salen) at polyestersulfonated ionomer coated electrodes in acetonitrile: Reactivity of the electrogenerated low-valent complexes

The electrochemical behaviour of [Ni(bpy)₃(BF₄)₂], [Co(bpy)₃(BF₄)₂], and Co(salen) (where bpy = 2,2′-bipyridine, and salen = N,N′-bis(salicylidene)ethylenediamine) is studied at a glassy carbon electrode modified with the poly(estersulfonate) ionomer Eastman AQ 55 in acetonitrile (MeCN). It is shown that the nickel complex is strongly incorporated into the polymer. The reduction of the divalent nickel compound features a two-electron process leading to a nickel(0) species which is released from the coating because of the lack of electrostatic attraction with the ionomer. Yet, the neutral zerovalent nickel-bipyridine complex is reactive towards ethyl 4-iodobenzoate and di-bromocyclohexane despite the presence of the polymer. The activation of the aryl halide occurs through an oxidative addition, whereas, an electron transfer is involved in the presence of the alkyl halide making the catalyst regeneration much faster in the latter case. The electrochemical study of [Co(bpy)₃(BF₄)₂] shows that incorporation of the cobalt complex into the polymer is efficient, provided excess bpy is used. This excess bpy does not interfere with the electrocatalytic activity of the cobalt complex incorporated in the AQ coating and efficient electrocatalysis is observed towards di-bromocyclohexane and benzyl-bromide as substrates. Finally, replacement of the bpy ligand with the macrocycle N,N′-bis(salicylidene)ethylenediamine, salen, leads to the incorporation of the non-charged Co^II(salen) complex into the AQ 55 polymer showing the relevancy of hydrophobic interactions. The reaction between the electrogenerated [Co^I(salen)]⁻ with 1,2-dibromocyclohexane exhibits a fast inner sphere electron transfer.     

Electro-oxidation of methanol on mixed catalysts based on platinum and organic metal complexes in acidic media

New electro-catalysts were developed based on platinum and organic metal complexes for methanol oxidation reaction (MOR) in acidic media. As complexes nitrogen containing ligands such as N,N′-bis(salicylidene)ethylenediamine (salen), N,N′-bis(salicylidene)phenylenediamine (salophen), N,N′-mono-8-quinolyl-o-phenylenediamine (mqph) and N,N′-bis(anthranilidene)ethylenediamine (anthen), coordinated to V, Mn, Fe, Co, Ni, Cu, Mo, Pd and Sn were synthesized and tested. Mixture of platinum tetraammine complex with one of the organic metal complexes with 50/50 mixing ratio was supported on carbon powder, and heat-treated at 400-700 °C in argon atmosphere. Powder, thus obtained was put on a glassy carbon disk electrode, and tested for electrochemical MOR in sulfuric acid solutions. Among catalysts tested, Fe(salen), VO(salen), Ni(mqph) or Pd(mqph) turned out to be good co-catalysts mixed with Pt for MOR. Compared with platinum-ruthenium alloy catalysts, the new catalysts showed very promising catalytic ability. It is inferred that after the heat treatment, the organic complex catalyst played a role in mitigating CO poisoning on Pt surface.     

XPS studies on the oxygen species of LaMn1−xCuxO3+λ

The electronic states of LaMn_1−xCu_xO_3+λ (x=0–0.4) have been studied with X-ray photoelectron spectroscopy (XPS). The valence states of substituted copper ions were Cu²⁺ and the manganese ions were a highly mixed state of Mn³⁺ and Mn⁴⁺. The nonstoichiometry and electronic state of lattice oxygen have been studied. The samples at x=0 and 0.1 had an excess of lattice oxygen but those at x=0.2–0.4 had lattice oxygen deficiency. A modified Auger parameter (Δ′) was used to evaluate the electronic states of oxygen ions. The Δ′ of lattice oxygen increased with increasing substitute quantity. This increase of Δ′ reflected the decrease of ionic bond character of lattice oxygen. The adsorbed oxygen species on LaMn_1−xCu_xO_3+λ was assigned mainly as O⁻ from the peak positions of spectra for the O 1s and O KLL levels, and the Δ′ of this O⁻ decreased with x. This decrease, i.e., the increase of ionic bond character of adsorbed oxygen was correlated well with the value of nonstoichiometry of lattice oxygen.

The rate of CO oxidation at 448 K was increased by the substitution till x=0.4. We consider that this enhancement of reactivity comes from the change of electronic state of adsorbed oxygen, O⁻ itself, i.e., a weak interaction between O⁻ and low coordinated metal site brings about a high reactivity.     

Near‐stoichiometric O2 binding on metal centers in Co(salen) nanoparticles

Co(salen) [cobaltous bis(salicylaldehyde)ethylenediamine] complexes are well‐known O₂ carriers in solution. In the solid phase, these complexes exhibit some O₂ binding but detailed studies have been complicated because few of the known polymorphs of Co(salen) actually bind O₂. The O₂ binding results for nanoparticulate Co(salen) are presented in this study. Rod‐shaped Co(salen) nanoparticles, roughly 100 nm in diameter, were recrystallized by spraying a methylene chloride solution of commercially obtained Co(salen) into supercritical carbon dioxide. Temperature‐programmed desorption, thermogravimetric analysis, and a Rubotherm magnetic suspension balance measurements reveal a reversible O₂ uptake of ～1.51 mmol/(g nanoparticles) at 25°C, consistent with a binding stoichiometry involving a bridging peroxo unit between two Co centers. In contrast, no measurable O₂ uptake was observed with the commercial Co(salen). These results clearly show the potential for bottom‐up design of nanoparticulate metal complexes for enhanced O₂ storage and other applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Oxygen sorptivity of mesoporous aluminosilicate modified by Co-salen complex

Mesoporous aluminosilicate, FSM-16 (Al-FSM-16(n)), was functionalized by Co-salen modification. The Si/Al ratio, n, was varied from 12.8 to 60.0, and inclusion of Co-salen (N,N^′-bis(salicylidene)ethylenediaminocobalt(II)) was carried out by a novel preparative method comprising Co²⁺ ion exchange in a nonaqueous solution of cobalt(II) acetate and chelation with salen-H₂ (N,N^′-bis(salicylidene)ethylenediamine). Prominent O₂ sorptivity was imparted to this mesoporous material and the amount of O₂ sorbed on Co-salen-Al-FSM-16(60.0) was 0.275 mmol g⁻¹ at 298 K, significantly larger than that on Al-FSM-16(60.0) itself (0.085 mmol g⁻¹). The O₂ sorption on Co-salen-Al-FSM-16(60.0) remarkably proceeded under a pressure around 20 kPa at 298 K, which was similar to powdery, free Co-salen. The maximum O₂/Co-salen ratio for Co-salen included in mesopores was seven times as large as that for neat Co-salen. The pore structure of Al-FSM-16(n) with a high n value was retained through the modification as evidenced by XRD, TEM and N₂ adsorption measurements, but that of Al-FSM-16(12.8) was partly collapsed.     

Density functional theory study on lithium bis[1,2-benzenediolato(2-)-O,O′] borate and its derivatives: electronic structures, energies, and molecular properties

Theoretical studies on electrolyte salts, lithium bis[1,2-benzenediolato(2-)-O,O′] borate (LBBB) and its derivatives, lithium bis[3-fluoro-1,2-benzenediolato(2-)-O,O′]borate (1FLBBB), and lithium bis[tetrafluoro-1,2-benzenediolato(2-)-O,O′] borate(4FLBBB) are carried out using density functional theory (DFT) method and B3LYP theory level for the first time. Bidentate structures involving two oxygen atoms are preferred. The GIAO–DFT results for all molecules suggest that the corresponding RB3LYP/6-31++G(2df,2p) geometries can be deemed reasonably good representations of the geometries of relatively free molecules in solution. Based on these conformations, a linear correlation was observed between the highest occupied molecular orbital (HOMO) energies and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that inorganic fluorine-containing anions are more resistant against oxidation than their organic counterparts. The correlations were also observed between ionic conductivity and binding energy, solubility and anion polarizability_, thermal stability and the energy difference between E_LUMO and E_HOMO. Wave function analyses have been performed by natural bond orbital (NBO) method to further investigate the cation–anion interactions.     

(CH3CH[NH3]CH2NH3)1/2·ZnPO4, a zincophosphate analogue of aluminosilicate zeolite thomsonite

The synthesis and structure of (CH₃CH[NH₃]CH₂NH₃)_1/2·ZnPO₄, an organically templated zincophosphate (ZnPO) analogue of aluminosilicate zeolite thomsonite (THO), are described. The ZnPO framework is built up from an alternating, vertex-sharing, network of ZnO₄ and PO₄ groups (d_av(Zn–O)=1.944 (8) Å, d_av(P–O)=1.535 (9) Å, θ_av(Zn–O–P)=130.5°) involving distinctive 4=1 secondary building units. The 1,2-diammonium propane cations are highly disordered in the [0 0 1] 8-ring channels. Crystal data: (CH₃CH[NH₃]CH₂NH₃)_1/2·ZnPO₄, M_r=198.42, orthorhombic, space group Pncn (no. 52), a=14.119 (6) Å, b=14.136 (5) Å, c=12.985 (5) Å, V=2591 (3) ų, Z=10, R(F)=0.057, R_w(F)=0.061 (for a twinned crystal).     

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.     

Probing the mechanistic aspects of the chromium salen catalyzed carbon dioxide/epoxide copolymerization process using in situ ATR/FTIR

Studies of the copolymerization of CO₂ and epoxides have been the staple of our group's research program for the better part of a decade now. During that time, the incorporation of attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy has greatly enhanced the kinetic and mechanistic investigations performed. However helpful, there are some difficulties, e.g., phase partitioning, that we have discovered and overcome in that same time period. The greatest step forward was achieved by the incorporation of 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (TMSO) as an epoxide for performing accurate kinetic studies. Herein, we discuss the development of this technique into one of the mainstays within our laboratories, highlighted by our most recent catalyst system that utilizes (salen)Cr^IIIX/cocatalyst where salen: N,N′-bis(salicylidene)-1,2-ethylenediimine, X: Cl⁻ or N₃⁻ and cocatalyst: N-methylimidazole, phosphines and PPN⁺ salts. Through altering the cocatalyst, ligand architecture and initiator, this catalyst system has proven to be one of the most industrially viable catalysts currently being studied.     

Electrochemistry and electrochromism of a poly(cyclopentadithiophene) derivative with a viologen pendant

N-Methyl-N′-(6-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-4-ylhexyl)-4,4′-bipyridinium dihexafluorophosphate (CPDT-V²⁺-Me) was synthesized. The monomer was electropolymerized on a glassy carbon or an ITO electrode in a potentiodynamic mode to form the corresponding polymer P(CPDT-V²⁺-Me) on the electrodes. During the electropolymerization, two redox peaks of the viologen (V) moiety increased up to several cycles and then decreased while the redox peak of P(CPDT) moiety still increased. Especially, a new oxidative peak a in the range of ca. −0.4 and 0 V versus Ag/Ag⁺ appeared and increased up to several cycles. Peak a almost disappeared after the redox peaks of the viologen moiety almost disappeared. As a result of cyclic voltammetric study, it was shown that peak a originated from the oxidation of reduced viologen moiety via P(CPDT)-mediated electron transfer mechanism. We also found that the electroactivity of viologen moiety in P(CPDT-V²⁺-Me) decreased significantly when the potential was scanned to the second viologen redox (V⁰/V√⁺). In practical applications, the polymer can be used in the potential range from the first viologen redox to P(CPDT) redox. The polymer turned into highly transparent P(CPDT⁺-V²⁺-Me), blue P(CPDT-V²⁺-Me), dark violet P(CPDT-V√⁺-Me), and violet P(CPDT-V⁰-Me) approximately at 0.8, −0.4, −0.8, and −1.7 V versus Ag/Ag⁺, respectively.     

Performance of La1−xSrxAl1−y−y′FeyMgy′O3−δ perovskites in methane combustion: effect of aluminum and magnesium content

Perovskites of different La_1−xSr_xAl_1−y−y′Fe_yMg_y′O_3−δ compositions (x=0, 0.1, 0.15, 0.2 and y=0.1, 0.3, 0.5, 0.8) were prepared from a reactive precursor slurry of hydrated oxides. Each sample was aged between 16 and 26 h up to 1473 K. Activity in methane combustion (1%/air) was determined in a plug-flow reactor, with 1 g catalyst and 24 l/h flowrate. Gradual decrease in activity due to thermal aging was observed, the degree of activity loss being composition dependent. Nevertheless, activity of samples aged at 1370 K was nearly independent of composition. The best thermal stability showed LaAl_0.65Fe_0.15Mg_0.2O₃ perovskite. None of the magnesium substituted perovskites performed better than a La_0.85Sr_0.15Al_0.87Fe_0.13O₃ reference sample.     

Investigation of the sol–gel transition of electrochemically prepared acrylamide bisacrylamide gels

A novel technique based on the chronoamperometric measurements was developed to study the sol–gel transition for the solution free radical cross-linking co-polymerization of acrylamide and N, N′-methylene bisacrylamide. The gels were synthesized electrochemically at room temperature in the presence of an initiator, ammonium persulfate. No chemical activator was used for accelerating the reaction; instead a direct voltage was applied by means of a silver-working electrode placed in the reaction mixture. It is found that the current measured during the gelation process monitors the change in the concentration of radicals, which are free to move in the reacting sample. The current due to these free radicals measures the weight average degree of polymerization and gel fraction around the gel point. Observations around the gel point, for low polymerization voltages, show that the gel fraction exponent β and the weight average degree of polymerization exponent γ agree with the mean-field results for low acrylamide concentrations. The samples synthesized above a certain voltage do not show self-similarity at the critical point. This is due to the increase in the local density, so does the heterogeneity, of the gel around the silver electrode, therefore, they do not obey the scaling behavior near the critical point.     

Dilute-solution behaviour of polyurethane ionomers

The behaviour of some polyurethane thiosulphate and sulphonate ionomers in dilute solutions is reported. Viscosity measurements of the ionomers in N,N′-dimethylformamide (DMF) showed a ‘polyelectrolyte effect’, which diminished upon addition of lithium bromide. For water-soluble ionomers, measurements were carried out in aqueous solution. The effect of the counterion was examined. Anomalous molecular-weight distributions of the ionomers were observed by gel permeation chromatography (g.p.c.) using DMF as solvent, which depended on the polymer ionic content, solution concentration and temperature. Normal g.p.c. distributions were obtained, however, in solvent containing 0.5% of lithium bromide.     

Selective oxidation of kraft lignin over zeolite‐encapsulated Co(II) [H4]salen and [H2]salen complexes

The Co([H₄]salen) and the corresponding Co([H₂]salen) complexes were encapsulated in NaY by the impregnation (IM) and flexible ligand ship‐in‐a‐botttle (SB) method for oxidation of kraft lignin to obtain chemical compounds. The neat and encapsulated complexes were characterized by XRD, FTIR, DR UV–Vis spectroscopy and BET, which showed the observed changes in the molecular structure to be correlated to the enhanced activity of the complexes. GC‐MS confirmed that the catalytic reactions of kraft lignin in the presence of peracetic acid produced major products including 2‐methoxy phenol, 2‐hydroxy benzaldehyde, 4‐hydroxy‐3,5‐dimethoxyphenyl ethanone. The encapsulated complexes exhibited improved reactivity compared to the corresponding neat complexes. Additionally, there was a greater improvement in TOF value for complexes upon IM‐immobilization as compared to SB‐immobilization. The improved salen, that is, [H₄]salen, was beneficial to the enhancement of catalytic activity as compared to [H₂]salen, as revealed by the high TOF values due to the incorporation of a modified coordination environment of the central cobalt cation by C=N hydrogenation. Actually, Co([H₄]salen)/IM was proved to be most active. Lignin conversion and TOF were high over the neat cobalt complexes when using 100% H₂O as the solvent, and the values were high over the corresponding encapsulated analogues when using 80% H₂O + 20% CH₃OH as the solvent. It can be found that encapsulation and hydrogenation of the complexes can improve the selectivity to 2‐methoxy phenol in the oxidation of kraft lignin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40809.