K-doped CuO/ZnO with dual active centers of synergism for highly efficient dimethyl carbonate synthesis

The application of heterogeneous catalysts in dimethyl carbonate (DMC) synthesis from methanol is hindered by low activation efficiency of methanol to methoxy intermediates (CH₃O*), which is the key intermediate for DMC generation. Herein, a catalyst of alkali metal K anchored on the CuO/ZnO oxide is rationally designed for offering Lewis acid–base pairs as dual active centers to improve the activation efficiency of methanol. Characterizations of CO₂-TPD, NH₃-TPD, XPS, and DRIFTS revealed that the addition of Lewis base K observably boosted the dissociation of methanol and combined with Lewis acid CuO/ZnO oxide to adsorb the formed CH₃O* stably, thus synergistically promoted the transesterification. Finally, the CuO/ZnO-9%K₂O catalyst exhibited the optimal catalytic activity, achieving a high yield of 74.4% with an excellent selectivity of 98.9% for DMC at a low temperature of 90°C. The strategy of constructing Lewis acid–base pairs provides a reference for the design of heterogeneous catalysts.     

Influence of cobalt oxide on the structure,optical transitions and ligand field parameters of lithium phosphate glasses

The influences of cobalt oxide (CoO) additions on the structure, optical transitions, ligand field parameters and stability of lithium phosphate glasses have been investigated. A series of glass systems (LiPhCo-glasses) was successfully prepared through the melt quenching approach. The amorphous nature was confirmed from X-ray diffraction measurements. The density and molar volume followed the typical opposite behavior, where the latter showed a decreasing behavior with CoO additions. Furthermore, it was found that the LiPhCo-glasses gradually changed their color from colorless (Co-free sample) into bluish glasses with CoO additions, thereby evidencing the presence of Co²⁺ ions. This is consistent with the absorption band identified in the optical absorption spectra at ~562–572 nm, which is related to ⁴A₂(⁴F) →⁴T₁(⁴P) electronic transitions of Co²⁺ (3d⁷ electronic configuration) in tetrahedral symmetry. Additional absorption band is detected at ~1412–1448 nm, which is correlated to ⁴A₂(⁴F) →⁴T₁(⁴F) transitions of Co²⁺ ions in tetrahedral symmetry. These two absorption bands were employed to study the ligand field splitting ($10D{q}_{\mathrm{t}}$)and Racah parameter (B), which sheds the light into the bonding character between Co ions and its ligands. The analysis showed that $10D{q}_t$ (B) is increased (reduced) indicating more covalency and less stability within the glass matrix with Co additions.     

FTIR and XPS study of the adsorption of probe molecule used to model alkyd resin adhesion to low carbon aluminum killed steel

An important factor in achieving maximum adhesion of a particular coating system to the substrate lies in the proper pre-treatment of the substrate prior to the application of the coating. The Lewis acid–base properties of the outer metal surface play a determining role in many of these applications, and the chemical reactions involved therein. In this work, the Lewis nature of the low carbon aluminum killed (LCAK) substrate has been significantly modified by a chemically activated surface pre-treatment. The wetting properties of the LCAK substrate was determined by contact angle measurements; the coordination of the chemical species on the surface was studied with XPS; FTIR together with the probe molecule (B(OCH₃)₃) was used to explain the chemical bonding. The novel combination of contact angle, XPS, FTIR and probe molecule enabled the determination of the Lewis acid–base properties of the LCAK surface before coating. The XPS spectra of the LCAK surface rinsed in warm water show that the surface species differ from that rinsed in tap water. With change in pH, the wettability properties also drastically changed. The probe molecule (B(OCH₃)₃) did not bond on the warm water rinsed samples but bonded strongly on tap water rinsed samples as the pH decreased. This research has shown that Lewis acid–base properties can be significantly changed with water temperature and pH, which has important implications for industrial pre-treatment.     

Feasible attachment of dinuclear ruthenium complex to gold electrode surface via new ligand substitution reaction

A general method has been developed for accumulation of a dinuclear ruthenium complex [Ru₂(dhpta)(μ-O₂CCH₃)₂]⁻ (H₅dhpta = 1,3-diamino-2-hydroxypropane-N,N,N′,N′-tetraacetic acid) on a gold surface. The accumulation using a ligand substitution reaction of bridging acetate in the complex by terminal benzoic acid in a self-assembled monolayer (SAM) with ω-mercaptoalkoxy benzoic acid (HOOC-C₆H₄-O-(CH₂)_n-SH) (n = 4, 6, 12) is undergone. The methyl benzoate-containing alkyl disulfides capable to form SAMs on gold electrode have been synthesized utilizing reductive dimerization of the corresponding alkyl thiocyanates with tetraphenylphosphonium tetrathiomolybdate. The methyl benzoate group in the SAM was converted into benzoic acid group by base hydrolysis, which was confirmed by surface-enhanced Raman scattering measurements for silver electrode. After the ligand substitution reactions to accumulate the complex on the gold electrode surface, in the case of n = 6 and n = 12, voltammetric waves for surface confined redox process, which corresponds to Ru^IIIRu^III/Ru^IIIRu^II redox couple are observed, respectively, and these surfaces of gold electrodes are covered with the complex completely. The present ligand substitution reaction should be widely applicable for the accumulation of other complexes and useful for designing of functional electrodes.     

Formation of Polymeric Lewis Acid–Lewis Base Complexes with Well-defined Organoboron Polymers

The binding of Lewis bases to organoboron polymeric Lewis acids has been studied and the parameters that determine the complexation equilibrium have been investigated, which include (i) the strength of the individual Lewis acids and Lewis bases, (ii) concentration, and (iii) temperature. While the strongly Lewis acidic borane polymers poly(4-bis(pentafluorophenyl)borylstyrene) (PS-BPf) and poly(4-(di-2-thienylboryl)styrene) (PS-BTh) form isolable complexes with strong Lewis bases such as 4-t-butylpyridine (^tPy), a temperature dependent equilibrium is established with weaker bases such as THF. Similarly, the weakly Lewis acidic boronate polymer poly(4-diethoxyborylstyrene) (PS-BOEt) undergoes a temperature dependent equilibrium with the strong Lewis base 4-dimethylaminopyridine (DMAP), while poly(4-pinacolatoborylstyrene) (PS-BPin) does not significantly bind to pyridine bases. Decomplexation of PS-BTh· ^t Py is achieved by treatment with the stronger Lewis acid, B(C₆F₅)₃, thereby confirming the reversible nature of the polymeric Lewis acid–base adducts. This paper is dedicated to Professor Ian Manners in gratitude of his guidance throughout the years and recognition of his scientific accomplishments     

Drastic ligand electronic effect on anilido-imino nickel catalysts toward ethylene polymerization

A novel nitro-anilido-imino nickel complex (Ar¹NCHC₆H₃(-5-NO₂)NAr²)NiBr (Ar¹ = Ar² = 2,6-dimethylphenyl) was designed, synthesized, and characterized to investigate ligand electronic effect on late transition metal olefin polymerization catalysts. As a catalyst for ethylene polymerization, neutral anilido-imino nickel complex with an electron-withdrawing nitro group showed good activity (442.1 kg (mol Ni h)⁻¹) with MAO as cocatalyst. The catalytic activity and molecular weight of the obtained products were significantly affected by electronic effect of the anilido-imine ligand. Theoretical calculations suggested that ligand electronic effect led to different charge distribution on the nickel metal atom, and the catalytic activity predominantly increased with an increase in electrophilicity of the nickel metal center.     

Reactions of methylbutynol on alkali-exchanged zeolites. A Lewis acid-base selectivity study

Alkali-exchanged zeolites have both Lewis acid and Lewis base centres. They provide an easy way to tune up the relative strengths of these two sites by controlling Si/Al ratio and electropositivity of the counter cation. These effects can be monitored both byFTIR and N_1s XPS of chemisorbed pyrrole. A systematic study of the relationship between acid-base properties and the reactions of methylbutynol (MBOH) was performed over these alkali-exchanged zeolites. The results show that the Lewis base centres catalyze the cleavage reaction ofMBOH, which produces acetone and acetylene, while the strong Lewis acid centres catalyze the dehydration ofMBOH to 3-methyl-3-buten-1-yne (MBYNE). The strong basicity of alkaliexchangedX zeolites produces almost 100% selectivity to acetone and acetylene, whereas the strong Lewis acidity of alkali-exchangedZSM-5 zeolites results in a high selectivity toMBYNE. Compared with the catalytic results overH-ZSM-5 zeolites, it is further concluded that the catalytic conversion ofMBOH to 3-methyl-3-butene-2-one (MIPK) requires the presence of not Lewis acid but strong Brønsted acid sites. The reactions ofMBOH over acid-base catalysts are considered as standard reactions for the characterization of acid and base centres. A correlation between these reactions and theFTIR, andXPS of pyrrole data will be discussed. The deactivation mechanism duringMBOH conversion over alkali-exchanged zeolites is further discussed.     

Synthesis and X-ray crystal structure of monomeric lanthanocene aryloxide complexes with a tridentate Schiff base ligand

Reaction of tris(cyclopentadienyl)lanthanide with the tridentate Schiff base N-1-(ortho-methoxyphenyl)salicylideneamine in THF at room temperature affords the isolation of monomeric lanthanocene Schiff base complexes, (η⁵-C₅H₅)₂Ln (OC₁₄H₁₃NO) (Ln=Sm (1), Er (2), Dy (3), Y (4)), which have been characterized by elemental analysis and mass spectra. The X-ray determination of 1 indicates that the complex is monomeric in which the metal center is coordinatively saturated by two cyclopentadienyl rings and two oxygens and one nitrogen from the Schiff base ligand. The average Sm–C bond distance is 2.723(7) Å, while those of the metal center to the Schiff base oxygens and nitrogen atoms are 2.232(4), 2.572(4) and 2.534(4) Å, respectively.     

Lewis acid–base property of P(VDF‐co‐HFP) measured by inverse gas chromatography

Poly (vinylidene fluoride‐co‐hexafluoropropylene) P(VDF‐co‐HFP) is an excellent material for polymer electrolytes of lithium ion battery. To enhance the lithium ion transference number, some metal oxides were often embedded into P(VDF‐co‐HFP). The promising mechanism for the increase in lithium ionic conductivity was Lewis acid‐base theory. In this experiment, the Lewis acid–base properties of P(VDF‐co‐HFP) were measured by inverse gas chromatography (IGC). The Lewis acid constant K_a of P(VDF‐co‐HFP) is 0.254, and the base constant K_b is 1.199. Compared with other polymers characterized by IGC, P(VDF‐co‐HFP) is the strongest Lewis basic polymers. Except aluminum ion, lithium ion is the strongest Lewis acidic ion according to their η value of Lewis acids. Therefore, a strong Lewis acid–base interaction will exist between lithium ion and P(VDF‐co‐HFP). This will restrict the transference of lithium ion in P(VDF‐co‐HFP). To enhance the lithium ion transference by blending other metal ions into P(VDF‐co‐HFP), it is suggested that the preferential ions should be Al³⁺, Mg²⁺, Na⁺, and Ca²⁺ because these metal ions have relative large η values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Titanium complexes supported by a sterically encumbering N-anchored tris-arylphenoxide ligand

A family of neutral and cationic Ti(IV) complexes supported by the sterically demanding and trianionic ligand (O₃N)³⁻ (O₃N³⁻ = tris(2-O,3-Ad,5-tBubenzyl)amine, Ad = 1-adamantyl) have been prepared from the hydrolysis of TiCl₄(THF)₂ with the free base (O₃N)H₃ and excess NEt₃, followed by anion exchange reactions. These (O₃N)Ti⁺ cores are resistant to moisture and air, are mononuclear, and possess C₃ symmetry on the NMR timescale.     

Helical metallomacrocyclic nickel(II) complexes of a tetradentate N2S2 ligand derived from N-methyldithiocarbazic acid

The structure of the tetradentate sulphur–nitrogen chelating agent, 1,2-phenylenebis(methylene) bis(1-methylhydrazinecarbodithioate) (NSSN) has been determined by X-ray diffraction. In the solid state, the two arms of the ligand remain in E configurations about the hydrazinic C–N bonds. The ligand reacts with hydrated nickel(II) salts in a 3:2 ligand-to-metal ratio yielding dimeric triple helical complexes of general formula, [Ni₂(NSSN)₃]X₄·nH₂O (X = Cl, Br, I, NCS; n = 5, 6, 9) which contain two nickel(II) ions in distorted octahedral environments. An X-ray crystallographic structure determination of the [Ni₂(NSSN)₃]Cl₄·9H₂O complex shows that it is a metallomacrocycle in which each ligand acts as a bis-bidentate chelating agent providing NS donors of one arm to one nickel(II) ion and NS donors of the second arm to a second nickel(II) ion. Each nickel(II) ion adopts a distorted octahedral geometry with a NiN₃S₃ coordination core as shown by their common electronic spectra.     

Novel ligation of some rare earth metal supramolecular polymer complexes

Summary Novel seven, nine and ten-coordinated rare earth polymer complexes of N-Acryloyl-1-phenyl-2-thiourea (APT) of the composition [Ln(NO₃)₃(APT)₂]_n (Ln = La, Sm, Tb, Pr and Nd) and [Ln(NCS)₃(APT)_x]_n (where Ln = La or Pr at x = 2 and Ln = Nd, Sm and Tb at x = 3 ) have been prepared and characterized on the basis of their chemical analyses, magnetic measurements, conductance, visible and IR spectral data. The electronic spectra of Pr³⁺, Nd³⁺ and Sm³⁺ show characteristic f-f transitions and the nephelauxetic effect (1-B) of these transitions has been evaluated. These data indicate the weak involvement of the 4f orbitals in complex formation. Composition and IR spectral data of the obtained polymeric complexes show that APT acts as a bidentate ligand. The structure and bonding of these high coordination number compounds were established and identified with the help of various physico-chemical studies. Conductance studies indicate a non-electrolytic behavior for these complexes. Their infrared spectra show that both the ligand and the nitrate group are bound to the metal ion in a bidentate fashion.     

Unusual dirhenium complexes containing the bis[2-(diphenylphosphino)phenyl]ether ligand including a terephthalate-bridged tetrarhenium compound

The synthesis, structures and reactivity of unsymmetrical multiply-bonded dirhenium(IV,II) and dirhenium(III,II) complexes that contain the bis[2-(diphenylphosphino)phenyl]ether ligand (L¹) are described, including the isolation and structural characterization of the novel terephthalate-bridged tetrarhenium complex [Re₂Cl₄(η³-L¹)]₂(μ-O₂CC₆H₄CO₂) in which there is weak electronic coupling between the pairs of dirhenium centers.     

Comparative Study of Lewis Acid Transformation on Non-reducible and Reducible Oxides Under Hydrogen Atmosphere by In Situ DRIFTS of Adsorbed NH<Subscript>3</Subscript>

The Lewis acid transformation to Bronsted acid was investigated over the Pt/γ-Al₂O₃ hybrid catalysts in the presence of hydrogen atmosphere by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed NH₃. The changes of FTIR spectra were monitored during the introduction of hydrogen at 40 °C and atmospheric pressure for 130 min. The degrees of Lewis acid transformation were varied by addition of non-reducible (SiO₂ and Al₂O₃) and reducible (ZrO₂, TiO₂ and CeO₂) oxides to the Pt/γ-Al₂O₃ catalysts as the hybrid catalysts. According to the in situ DRIFTS, the hydrogen temperature programmed reduction (H₂-TPR), and the hydrogen temperature programmed desorption (H₂-TPD) results, the introduction of hydrogen resulted in a decrease in the amount of ammonia adsorbed on Lewis acid sites, and an increase in the amount of ammonium ions on Bronsted acid sites with time on stream. It is proposed that ammonia migration from Lewis acid sites to Bronsted acid sites occurred during the introduction of hydrogen in the presence of Pt particles when compared to the observation of only observed catalysts (without Pt particles). The addition of reducible oxides led to the high rate of Lewis acid transformation, which was higher than those of the non-reducible oxides. Weaker Lewis acid sites and higher amount of hydrogen spillover over the observed catalysts enhanced the rate of Lewis acid transformation in this study. However, the amount of Lewis acid sites at the initial stage did not play an important role in these transformations.     

A New 2D Porous Pb-MOF Based on Ribbon‐Shaped SBU and 2-Nitroimidazole: Structure and Properties

A new porous metal-organic framework, [Pb₅(OAc)₇(nIm)₃]_n (1), has been successfully synthesized by employing 2-nitroimidazole ligand and Pb²⁺ ion. 1 contains novel the ribbon-shaped Pb-O SBU and reveals a 2D porous framework with a 1D tubular channel. Due to the existence of the electronegative O atom of nitro group and Lewis acid metal ion in the channel, 1 shows moderate CO₂ adsorption uptake of 25.8 cm³ cm^??1 at 298 K and 760 mmHg, and adsorption sites are also confirmed by GCMC simulations. Moreover, the electronic structures and luminescence properties of 1 was investigated. This work displays an effective approach to enrich multifunctional porous Pb-MOFs.

     

Low band gap Schiff base polymers obtained by complexation with Lewis acids

Two Schiff base polymers were prepared from the respective monomers by condensation method using toluene and N-methyl-2-pyrrolidinone as solvent. They were complexed with Al(III), In(III), and Cu(II) trifluoromethane sulfonates (triflates), and AlCl₃ Lewis acids and characterized by FT-IR, UV–Vis spectroscopy, and scanning electron microscopy (SEM). Homogeneous films were prepared by spin coating in the presence and absence of Lewis acids. Polymer–Lewis acid interaction was confirmed by FT-IR, UV–Vis spectroscopy, and SEM. Lewis acid composition in polymers was determined by FT-IR spectroscopy. Absorption spectra of these conjugated Schiff base polymer complexes exhibited smaller optical band gap than pristine polymers. These variations ranged from 2.4 to 1.4 and 3.3 to 2.0 eV. Absorption depends on the Lewis acid in the polymer and band gap on the nature of the metal incorporated in the polymeric backbone. Solubility increased by complexation. The obtained complexes were soluble in trifluoroacetic and formic acids and in m-cresol. Polymer–Lewis acid solutions in m-cresol were stable for 98 h; the others remained stable over several months. The results of this study revealed that optical, solubility, and band-gap properties of conjugated Schiff base polymers can be modified by Lewis acids and these could be studied by optoelectronics.     

Uranyl ion complexation by the tripodal ligand nitrilotriacetate

Reaction of uranyl nitrate with N-(2-acetamido)iminodiacetic acid (ADA) under hydrothermal conditions resulted in the hydrolysis of the amide group and the isolation of the complex [(UO₂)(HNTA)(H₂O)₂], in which each nitrilotriacetate ligand, protonated at the N site, bridges three metal atoms to give rise to infinite ladder-like ribbons built from 2:2 metallacycles.     

Acylation desulfurization of oil via reactive adsorption

Excellent desulfurization is achieved via reactive adsorption using Friedel‐Crafts acylation materials, that is, acylating reagents and Lewis acids, such as acetyl chloride (AC) and AlCl₃, being named as acylation desulfurization (ACDS). For model oil, thiophenic compounds, namely, dibenzothiophene, benzothiophene, and thiophene, are removed completely by AC–AlCl₃ within 30 min at room temperature. In this process, thiophenic compounds are acylated by AC under the catalysis of AlCl₃, and the acylated derivatives are stronger base than original ones due to incorporation of O‐containing carbonyl group (C?O) and, thus, adsorbed more easily by AlCl₃ via Lewis acid–base complexation. Further, ACDS mechanism is identified by acylated product characterization and quantum chemistry calculation. Satisfactorily, ACDS is still effective for toluene‐rich and real oils, and real oil quality is improved with desulfurization proceeding. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2966–2976, 2013     

Evidence of Correlation between Electronic Density and Surface Acidity of Sulfated TiO2

Correlation between the electronic structure and surface acidity of TiO₂–SO₄ ^2– with different SO₄ ^2– amounts has been investigated by means of NH₃-TPD, NH₃-FT-IR and XPS. With the increase of sulfate loadings, the shift of binding energies of O 1s in hydroxyl and Ti 2p_2/3 increases and is proportional to total acidity. A linear relation is obtained between Ti 2p binding energy shift and Lewis acid sites, while the shift in O 1s binding energy is attributed both to the generation of NH₃ hydrogen bond and of Brønsted acid sites. Accordingly, the results obtained from XPS measurements provide evidence that the ammonia adsorption sites are attributed to the decrease of electron density of O 1s in hydroxyl (Brønsted type and H bonded) and Ti 2p_2/3 (Lewis type) by inductive effect of the neighboring sulfate ion.     

Characterization of asymmetric hollow fibre membranes with graded-density skins

Asymmetric hollow fibre membranes can be prepared from polysulphone, polyethersulphone, and polyphenylsulphone by phase inversion from Lewis acid:base complex solvent systems. Formation of a complex from the non-solvent (Lewis acid) and the solvent (Lewis base) permits higher concentrations of non-solvent to be included in the spinning dope than can be added with traditional solvent/non-solvent mixtures. These membranes exhibit gas permeation rates which are a multiple of those obtained with membranes fabricated from traditional solvent/non-solvent mixtures as well as maintenance of selectivity. This enhancement in permeation performance results primarily from the creation of a skin structure with a much thinner effective separating layer than can be obtained from spinning processes utilizing solvent/non-solvent mixtures. However, it is also believed that these membranes possess enhanced free volume which is derived from the kinetics of the sol-to-gel transition. The rapid dissociation of the Lewis acid:base complex by contact with water accelerates the coagulation process, which limits conformational rearrangement. The dissociation of the Lewis acid:base complex into smaller moieties facilitates their removal from the nascent hollow fibre membranes. The acceleration of the coagulation process increases the free volume in the resultant membrane, which is reflected by an increase in the glass transition temperature that disappears upon annealing. This increase is readily seen during the first heat in a DSC scan, and it is believed that this increase is not a result of superheating, which yields the ‘T_g overshoot’ commonly observed in glassy polymers annealed below their glass transition temperatures.