DISCOVERY OF SPECIAL PREDOMINANCE OF VANADYL PORPHYRIN AND HIGH ABUNDANCE OF Di-DPEP IN NONMARINE STRATA

By means of TLC, UV-Vis, HPLC and MS analyses, the types, structure and fingerprint distribution of porphyrin compounds in the nonmarine strata of China have been studied herein. It is revealed that the predominance of vanadyl porphyrin in lacustrine sediments of the Ordos Basin resulted from the high maturity, while the abnormal high content of Di-DPEP in the boghead-cannel coal from Guizhou Province was probably related to its abundant source input, the weakly oxidizing condition during the early diagenesis and the consequent reducing environment.     

Crystallographic report: Bis(3‐methyl‐2‐cyclopenten‐1‐one)dichloro‐oxovanadium(IV)

The crystal structure of the oxovanadium(IV) complex (CH₃C₅H₅O)₂VOCl₂ was determined. The molecule has trigonal bipyramidal geometry, with oxygen atoms of cyclopentenones in axial positions and oxygen and two chlorine atoms in equatorial positions. Copyright © 2005 John Wiley & Sons, Ltd.     

Y-型沸石上VO(H2O)42+的ESR波谱研究

本文报道了VO²⁺在Y型沸石上用不同温度灼烧处理之后测得的两种不同的ESR波谱。提出了VO(H₂O)₄²⁺离子在沸石笼中的两种可能结构,随着灼烧温度的升高,结构(Ⅰ)减少。到灼烧温度高于600。C时则结构(Ⅰ)完全消失,而对应于结构(Ⅱ)的A_⊥也渐渐变小,说明未偶电子离域性增大以致失去电子,V⁴⁺则被氧化成V⁵⁺。本文利用波谱参数计算了键参数和约化能级。     

CRYSTAL STRUCTURE INVESTIGATION OF VANADYL COMPLEXES OF TRIDENTATE LIGAND (Ⅱ)——SYNTHESE AND CRYSTAL STRUCTURE OF 1-(2-PYRIDYLAZO)-2-NAPHTHOLATO-DIOXOVANADIUM (Ⅴ) DIMER [VO_2(C_(15)H_(10)N_3O)]_2(H_2O_2)(CHCl_3)_2 AND PYRIDINE-(1-(2-PYRIDYLAZO)-2-NAPH

The title complexes crystallize in space groups C(?)-P(?) and C_(2h)~5-P2_1/c, and with unit cell parameters a=8.488. b=10.100, c=11.974. α=72.73°, β=78.56°, γ=73.55°, and a=11.496, b=9.883. c=16.360, β=100.18°, respectively. All the V coordinates are obtained from Patterson and direct methods, respectively, and then Fourier and difference Fourier methods are employed to deduce other non-hydrogen atoms. Structural parameters are refined with least-squares technic, yielding final discrepancy factors R=0.081 and 0.067, respectively. Structural analyses demonstrate that the dimer of VO_2~+ complex is formed through the sixth-position bonding of a bridge oxygen atom of one VO_2~+ group with another VO_2~+, and the formation of VO(O_2)(C_(15)H_(10)N_3O)(C_5H_5N) shows that VO~(2+) complex with strong chelating tridentate PAN-seems less difficult to transform into the pentagonal bipyramid VO~(3+) complex. Since no peroxo species has been used in the synthesis, the fact that a peroxo group forms in the     

Volumetric method for following the rate of intercalation of liquid molecular guests into layered hosts

A new experimental method is suggested for the kinetic measurements of intercalation reactions in systems formed by a polycrystalline layered host and a liquid molecular guest. The method is based on the fact that the molecular guest decreases its molar volume on entering the space between the host layers. Hence the volume of the system in which an intercalation process takes place is measurably decreased. The time course of the intercalation process can thus be monitored by measuring the volume change of the system. The method has been used to obtain kinetic data about heterogeneous intercalations of some liquid aliphatic compounds into layered structures of anhydrous vanadyl phosphate and sulfate.     

Towards Reversible High-Voltage Multi-Electron Reactions in Alkali-Ion Batteries Using Vanadium Phosphate Positive Electrode Materials

Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V²⁺ to V⁵⁺) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. for V³⁺/V⁴⁺ in Na₃V₂(PO₄)₂F₃) could allow the achievement the 1 kWh/kg milestone at the positive electrode level in Alkali-ion batteries. However, a massive divergence in the voltage reported for the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ redox couples as a function of crystal structure is noticed. Moreover, vanadium phosphates that operate at high V³⁺/V⁴⁺ voltages are usually unable to reversibly exchange several electrons in a narrow enough voltage range. Here, through the review of redox mechanisms and structural evolutions upon electrochemical operation of selected widely studied materials, we identify the crystallographic origin of this trend: the distribution of PO₄ groups around vanadium octahedra, that allows or prevents the formation of the vanadyl distortion (O^…V⁴⁺=O or O^…V⁵⁺=O). While the vanadyl entity massively lowers the voltage of the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ couples, it considerably improves the reversibility of these redox reactions. Therefore, anionic substitutions, mainly O²⁻ by F⁻, have been identified as a strategy allowing for combining the beneficial effect of the vanadyl distortion on the reversibility with the high voltage of vanadium redox couples in fluorine rich environments.     

Chiral vanadyl salen complex anchored on supports as recoverable catalysts for the enantioselective cyanosilylation of aldehydes. Comparison among silica, single wall carbon nanotube, activated carbon and imidazolium ion as support

The activity and enantiomeric excess (ee) (in some cases >85%) obtained for the asymmetric addition of trimethylsilyl cyanide to aldehydes using different heterogeneous chiral catalysts are compared. A library of recoverable catalysts was developed by immobilization of a chiral vanadyl salen complex having a terminal carbon-carbon double bond onto a series of scaffolds including silica, single-wall carbon nanotubes, activated carbon and room-temperature ionic liquids. The covalent linkage has been achieved by radical initiated addition of mercapto groups to CC. The highest enantiomeric excesses, similar to those obtained in the homogeneous phase, were achieved using silica as support or with the homogeneous tetra-tert-butyl salen catalyst dissolved in an imidazolium ionic liquid. The use of silica as support permits an easier separation and reuse of the catalyst from the reaction media.     

Nafion®‐supported oxovanadium‐catalyzed hydrophosphonylation of aldehydes under solventless conditions

A Nafion® resin‐supported oxovanadium(IV) catalyst was readily prepared via ion‐exchange method. This solid vanadyl perfluorinated sulfonate catalyst was used as an efficient and recoverable catalyst for the hydrophosphonylation of various aldehydes under solventless conditions at room temperature. The catalyst could be recovered by simple filtration and reused without a significant loss of activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Electronic State of Vanadium Ions in Li1+xV3O8 According to EPR Spectroscopy

EPR spectroscopy is used to study the electronic state of vanadium ions in HT- and LT-Li_1+xV₃O₈. It is shown that in both cases the EPR spectra observed are attributed to vanadyl VO²⁺ ions (localized electron centers) with weak exchange interaction. The other type of registered electrons is characterized by larger mobility through a few V⁵⁺ ions, i.e., by a higher degree of delocalization (electron gas). Based on the analysis of the temperature dependence of the EPR line width, it is stated that the exchange interaction between localized electron centers proceeds through electron gas (C-S-C relaxation). It is found that HT-Li_1+xV₃O₈ differs from LT-Li_1+xV₃O₈ by the sloping form of its spectrum at g_∥ range connected with two types of VO²⁺ ions different in the direction of the crystal field axis corresponding to a short V=O²⁺ bond.     

EPR spectra of V(IV) complexes and the structure of oil porphyrins

For natural bitumoids, the effects of the structure of vanadyl-porphyrin complexes on the EPR spectra were investigated. The ambiguity of the hyperfine structure (its presence or absence) corresponding to four nitrogen atoms in the spectra of oil vanadyl porphyrins correlates with the changes in the second coordination sphere of the nearest environment of the metal ion, namely, in methine bridges.