Isolation and Spectroscopic Characterization of New Endohedral Fullerenes in the Size Gap of C74 to C76

New alkaline earth metal endohedral fullerenes Sr@C₇₄, Sr@C₇₆‐I, II and Ca@C₇₄, prepared by means of the RF‐method, have been isolated using multistep HPLC. The purity was ascertained by anionic LDI TOF mass spectroscopy, considering the isotopic patterns of the compounds. The influence of the incorporated metal on the electronic structure has been studied by VIS‐NIR and Raman spectroscopy. Photoexcited triplet‐state EPR spectroscopy was used to investigate the structure of these otherwise EPR‐silent fullerenes. Displaying the frequency of the cage vs. encapsulated metal vibrational modes as a function of the square root of the reciprocal masses of the metals clearly separates the M³⁺@C_n^3— and the M²⁺@C_n^2— families. This seems to be a generally applicable tool for monitoring the metal to fullerene charge transfer.     

Highly Efficient Low‐Temperature Plasma‐Assisted Modification of TiO2 Nanosheets with Exposed {001} Facets for Enhanced Visible‐Light Photocatalytic Activity

Anatase TiO₂ nanosheets with exposed {001} facets have been controllably modified under non‐thermal dielectric barrier discharge (DBD) plasma with various working gas, including Ar, H₂, and NH₃. The obtained TiO₂ nanosheets possess a unique crystalline core/amorphous shell structure (TiO₂@TiO_2?x), which exhibit the improved visible and near‐infrared light absorption. The types of dopants (oxygen vacancy/surface Ti³⁺/substituted N) in oxygen‐deficient TiO₂ can be tuned by controlling the working gases during plasma discharge. Both surface Ti³⁺ and substituted N were doped into the lattice of TiO₂ through NH₃ plasma discharge, whereas the oxygen vacancy or Ti³⁺ (along with the oxygen vacancy) was obtained after Ar or H₂ plasma treatment. The TiO₂@TiO_2?x from NH₃ plasma with a green color shows the highest photocatalytic activity under visible‐light irradiation compared with the products from Ar plasma or H₂ plasma due to the synergistic effect of reduction and simultaneous nitridation in the NH₃ plasma.     

The Growth of Co:ZnO/ZnO Core/Shell Colloidal Quantum Dots: Changes in Nanocrystal Size,Concentration and Dopant Coordination

We report a synthesis route for the growth of Co:ZnO/ZnO core/shell quantum dots. This procedure consists of successive steps, comprising the addition of diluted precursor salt solutions, and heat treatment at 50 °C. By deriving a relation between the extinction coefficient at 250 nm and the nanocrystal diameter, we are able to monitor changes in quantum dot concentration during shell growth. We found that a mechanism based on the nucleation of new particles after salt addition and subsequent Ostwald ripening during the heat treatment is responsible for the shell growth. Based on ligand‐field absorption spectroscopy, we demonstrate that the Co²⁺ ions adsorbed at the surface of Co:ZnO quantum dots are incorporated inside the ZnO shells. Finally, EPR spectroscopy indicates that the surface‐adsorbed Co²⁺ ions can be incorporated as substitutional as well as interstitial Co²⁺ ions.     

O,N‐Chelated Vanadium(IV) Oxo Aminophenolate Complexes: the Effect of Steric Bulk on the Vanadium Coordination Geometry. Can this Influence be detected Spectroscopically?

In order to study the effect of steric bulk on the vanadium coordination geometry in O, N‐chelated vanadium oxo (bis)phenolates, six different ortho‐aminophenolate ligands have been used. The ortho‐aminophenolate system was changed at three different places, i.e. 1) the second ortho position (C⁶) of the arene ring (R), 2) the substituents at the amino nitrogen (R′ and R″), and 3) the benzylic carbon atom (R*). The phenols were used in the preparation of the vanadium oxo (bis)phenolate complexes. In order to study whether it is possible to predict geometrical features of these vanadium complexes, UV/Vis, solution and frozen state EPR and ¹⁴N ESEEM spectroscopic data was measured and compared to the structural features of four structurally characterized vanadium oxo (bis)phenolates. Unfortunately, it turned out that is was not possible to correlate the EPR parameters, the UV/Vis HOMO‐LUMO transitions or ¹⁴N hyperfine couplings to the structural parameters.     

氨法选择性还原氮氧化物 V2O5/TiO2-PILC催化剂的抗硫性能

选择性催化还原(SCR)是目前去除氮氧化物最有效的方法之一. V2O5/TiO2催化剂被广泛应用于氨法选择性还原氮氧化物(NH3-SCR)反应,但该催化剂存在工作温度高(300–400oC)及 SO2氧化率高引起设备腐蚀和管路堵塞等问题,开发低温 SCR催化剂具有重要意义.过渡金属氧化物(如 Fe2O3, MnOx和 CuO等)催化剂用于低温SCR先后见诸文献报道,但这些催化剂在 SO2和 H2O存在下易失活.近年来柱撑黏土(PILC)引起科学家广泛关注, Yang等首次将 V2O5/TiO2-PILC催化剂应用于 NH3-SCR反应,发现其催化活性高于传统 V2O5/TiO2催化剂.柱撑黏土基催化剂在 NH3-SCR反应中也显示出良好抗硫性能,但 V2O5/TiO2-PILC催化剂的抗硫机理至今尚未见深入研究.因此我们制备了一系列 V2O5/TiO2-PILC催化剂,采用原位漫反射红外等方法详细研究了其抗硫性能较好的原因.
　　首先采用离子交换法制备出 TiO2-PILC载体,之后采用浸渍法制备了不同钒含量(质量分数x/%=0,3,4,5)的xV2O5/TiO2-PILC催化剂.同时,制备了传统 V2O5/TiO2和 V2O5-MoO3/TiO2催化剂作为对比.活性评价结果显示,4V/TiO2-PILC催化剂具有最高的催化活性,其催化性能与传统钒钛催化剂相当.在160oC时, NO转化率可达80%以上.同时,4V/TiO2-PILC催化剂还具有较宽的反应温度窗口,在260–500oC范围内, NO转化率保持在90%以上.向反应体系中加入0.05% SO2和10% H2O后,在低温(160oC以下)时所有催化剂的反应活性都有一定提高,可能是由于 SO2的加入提高了催化剂的表面酸性.继续升高温度,4V/TiO2和4V6Mo/TiO2催化剂活性均明显下降,而4V/TiO2-PILC催化剂的活性则未出现明显下降.原位漫反射红外光谱结果显示, SO2在三种催化剂表面的吸附以表面硫酸盐或亚硫酸盐物种以及离子态 SO42–物种形式存在,而在4V/TiO2-PILC催化剂表面离子态 SO42–物种的量最少. X射线光电子能谱及 O2程序升温脱附结果显示,在4V/TiO2-PILC催化剂上,表面吸附氧(Oads)的量最少.综合上述分析可以得出,在 SO2气氛下,离子态 SO42–物种在 SCR催化剂表面的累积可能是导致其失活的主要原因,而离子态 SO42–物种的形成可能与催化剂表面吸附氧的量有关.     

The Influence of Defects on Mo‐Doped TiO2 by First‐Principles Studies

TiO₂ doped with transition metals shows improved photocatalytic efficiency. Herein the electronic and optical properties of Mo‐doped TiO₂ with defects are investigated by DFT calculations. For both rutile and anatase phases of TiO₂, the bandgap decreases continuously with increasing Mo doping level. The 4d electrons of Mo introduce localized states into the forbidden band of TiO₂, and this shifts the absorption edge into the visible‐light region and enhances the photocatalytic activity. Since defects are universally distributed in TiO₂ or doped TiO₂, the effect of oxygen deficiency due to oxygen vacancies or interstitial Mo atoms is systemically studied. Oxygen vacancies associated with the Mo dopant atoms or interstitial Mo will reduce the spin polarization and magnetic moment of Mo‐doped TiO₂. Moreover, oxygen deficiency has a negative impact on the improved photocatalytic activity of Mo‐doped TiO₂. The current results indicate that substitutional Mo, interstitial Mo, and oxygen vacancy have different impacts on the electronic/optical properties of TiO₂ and are suited to different applications.     

Spatially resolved Raman and UV-visible-NIR spectroscopy on the preparation of supported catalyst bodies: controlling the formation of H2PMo11CoO40 5- inside Al2O3 pellets during impregnation

The physicochemical processes that occur during the preparation of CoMo-Al2O3 hydrodesulfurization catalyst bodies have been investigated. To this end, the distribution of Mo and Co complexes, after impregnation of gamma-Al2O3 pellets with different CoMoP solutions (i.e., solutions containing Co, Mo, and phosphate), was monitored by Raman and UV-visible-NIR microspectroscopy. From the speciation of the different complexes over the catalyst bodies, insight was obtained into the interaction of the different components in the impregnation solution with the Al2O3 surface. It is shown that, after impregnation with a solution containing H2PMo11CoO40(5-), the reaction of phosphate with the Al2O3 leads to the disintegration of this complex. The consecutive independent transport of Co2+ complexes (fast) and Mo6+ complexes (slow) through the pores of the Al2O3 is envisaged. By the addition of extra phosphate and citrate to the impregnation solution, the formation of the desired heteropolyanion can be achieved inside the pellets. Ultimately, the H2PMo11CoO40(5-) distribution could be controlled by varying the aging time applied after impregnation. The power of a combination of spatially resolved spectroscopic techniques to monitor the preparation of supported catalyst bodies is illustrated.     

The reaction mechanism of p-toluenediamine anodic oxidation: an in situ ESR-UV/Vis/NIR spectroelectrochemical study.

In situ ESR-UV/Vis spectroelectrochemistry is applied to obtain new insights into the intermediates and reaction products of the anodic oxidation of p-toluenediamine in aqueous solution at different pH values. A strong pH dependence of the stability of the cation radical is found. While the absence of a stable radical was proved by ESR spectroscopy at pH 2 and 10, this radical is detected at medium pH values and assigned to the semiquinonediimine structure. The UV/Vis absorption of the radical is observed at these pH values as well. The p-toluenediimine intermediate and the trimeric reaction product were followed during the electrode reaction by UV/Vis spectroscopy at all pH values.     

Non‐UV‐Induced Radical Reactions at the Surface of TiO2 Nanoparticles That May Trigger Toxic Responses

Kept in the dark : The non‐photocatalytic generation of free radicals from fine and ultrafine TiO₂ particles has been studied by means of a spin‐trapping/ESR spectroscopy technique (see figure). The amount and kind of free radicals generated depends on the crystalline structure, but not on the particle dimensions.

     

9,10‐Diaminoanthracenes Revisited: The Influence of N‐Substituents on Their Electronic States

The electronic and molecular structures of 9,10‐diamino‐substituted anthracenes with different N‐substituents have been re‐examined. In particular, different N‐substituents influence both the electronic and molecular structures of the oxidized species of 9,10‐diaminoanthracenes. The anthrylene moiety of 9,10‐bis(N,N‐di(p‐anisyl)amino)anthracene retains its planarity during the course of two successive one‐electron oxidations, whereas 9,10‐bis(N,N‐dimethylamino)anthracene and 9,10‐bis(N‐p‐anisyl‐N‐methylamino)anthracene undergo a substantial structural change to a butterfly‐like structure through a two‐electron oxidation process. The structural changes observed for the oxidized states are ascribed to significant differences in the frontier molecular orbitals of the above‐mentioned three kinds of 9,10‐diaminoanthracenes due to different extents of mixing between the amine‐localized and anthrylene‐localized orbitals.     

Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites

The locations of Brønsted acid sites (BAS) in the channels of medium‐pore zeolites have a significant effect on the spontaneous ionization of para‐terphenyl (PP₃) insofar as spatial constraints determine the stability of transition states and charge‐transfer complexes relevant to charge separation. The ionization rates and ionization yield values demonstrate that a strong synergy exists between the H⁺ polarization energy and spatial constraints imposed by the channel topology. Spectroscopic and modeling results show that PP₃ incorporation, charge separation, charge transfer and charge recombination differ dramatically among zeolites with respect to channel structure (H‐FER, H‐MFI, H‐MOR) and BAS density in the channel. Compartmentalization of ejected electrons away from the initial site of ionization decreases dramatically the propensity for charge recombination. The main mode of PP₃^.+ decay is hole transfer to form AlO₄H^.+ ??? PP₃ charge‐transfer complexes characterized by intense absorption in the visible range. According to the nonadiabatic electron‐transfer theory, the small reorganization energy in constrained channels explains the slow hole‐transfer rate.     

New Pentacoordinated Rhodium Species as Unexpected Products during the In Situ Generation of Dimeric Diphosphine‐Rhodium Neutral Catalysts

Dimeric rhodium complexes of the type [Rh(PP)(μ₂‐Cl)]₂ (PP=diphosphine) are often used as precatalysts and are generated “in situ” from the corresponding diolefin complexes by exchange of the diene with the desired diphosphine. Herein, we report that the “in situ” procedure also leads to unexpected monomeric pentacoordinated neutral complexes of the type [RhCl(PP)(diolefin)], for the first time herein characterized by NMR spectroscopy and X‐ray crystallography for the ligands 1,4‐bis(diphenylphosphino)propane (DPPP), 1,4‐bis(diphenylphosphino)butane (DPPB), and 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP). The pentacoordinated complexes are in equilibrium with the dimeric target compound [Rh(PP)(μ₂‐Cl)]₂. The equilibrium is influenced by the rhodium‐diolefin precursor, the solvent and the temperature. Based on the results of NMR and UV/Vis spectroscopic analysis (kinetics) it could be shown that the pentacoordinated complex [RhCl(PP)(diolefin)] may arise both from the “in situ”‐generated neutral complex [Rh(PP)(μ₂‐Cl)] by reaction with the free diolefin and, more surprisingly, directly from [Rh(diolefin)(μ₂‐Cl)]₂ and the diphosphine.     

Spatially Heterogeneous Nature of Self‐Catalytic Reaction in Hetero‐Double Helix Formation of Helicene Oligomers

A 1:1 mixture of pseudoenantiomeric aminomethylenehelicene oligomers, (P)‐tetramer and (M)‐pentamer, in fluorobenzene show a self‐catalytic phenomenon in the formation of hetero‐double helices from random coils. This study visualizes the spatially heterogeneous nature of the self‐catalytic reaction in dilute solution. UV/Vis imaging analysis of the mixture at 70 °C, containing random coils, exhibits a homogeneous bright area. When the solution is cooled from 70 to 30 °C and held at that temperature, dark domains of approximately 1 mm in size appear, which move approximately at a rate of 1 mm min^?1. The dark domains indicate that weaker UV/Vis absorption results from the formation of hetero‐double helices, which is supported by circular dichroism (CD) imaging experiments. Then a homogeneous mixture is regenerated upon heating to 55 °C, as shown by CD imaging. Under self‐catalytic conditions, a homogeneous solution spontaneously changed to a heterogeneous solution in the process of hetero‐double‐helix formation.     

Small‐Peptide‐Based Organogel Kit: Towards the Development of Multicomponent Self‐Sorting Organogels

The results presented here highlight the extremely useful nature of ultra‐short peptides as building blocks in the development of smart multicomponent supramolecular devices. A facile bottom‐up strategy for the synthesis of a small library of stimuli‐responsive smart organogelators has been proposed based on the predictive self‐assembly of ultra‐short peptides. More importantly, the narcissistic self‐sorting of the gelators has been evaluated as a simple method for the efficient co‐assembly of a donor–acceptor dual‐component gel, allowing the investigation of possible future applications of similar systems in the development of a supramolecular photo‐conversion device. Interestingly, it was observed that the self‐organization of the components can lead to highly ordered systems in which discrimination between compatible and non‐compatible building blocks directs the effective organization of the chromophores and gives rise to the formation of an excited‐state complex with exciplex‐like emission. The current report may prove important in the development of organogel‐based multicomponent smart devices.     

Heterogeneous Photochemistry Relevant to the Troposphere: H2O2 Production during the Photochemical Reduction of NO2 to HONO on UV‐Illuminated TiO2 Surfaces

Bleached out: The detection of an oxidized co‐product, hydrogen peroxide, during an important tropospheric reaction, combined with the detection of photoaccelerated surface nitrate formation (a competing pathway), allows a likely mechanism to be proposed (see figure) which explains previously observed experimental stoichiometries.

     

Harnessing Electron Transfer from the Perchlorotriphenylmethide Anion to Y@C82(C2v) to Engineer an Endometallofullerene‐Based Salt

We show that electron transfer from the perchlorotriphenylmethide anion (PTM^?) to Y@C₈₂(C_2v) is an instantaneous process, suggesting potential applications for using PTM^? to perform redox titrations of numerous endohedral metallofullerenes. The first representative of a Y@C₈₂‐based salt containing the complex cation was prepared by treating Y@C₈₂(C_2v) with the [K⁺([18]crown‐6)]PTM^? salt. The synthesis developed involves the use of the [K⁺([18]crown‐6)]PTM^? salt as a provider of both a complex cation and an electron‐donating anion that is able to reduce Y@C₈₂(C_2v). For the first time, the molar absorption coefficients for neutral and anionic forms of the pure isomer of Y@C₈₂(C_2v) were determined in organic solvents with significantly different polarities.