We are pleased to announce that the CIQTEK EPR spectrometer products have contributed to 27 high-level research publications to date!
One of the Selected Results
Vanadium-Catalyzed Dinitrogen Reduction to Ammonia via a [V]═NNH2 Intermediate.
Journal of the American Chemical Society (2023)
Wenshuang Huang, Ling-Ya Peng, Jiayu Zhang, Chenrui Liu, Guoyong Song, Ji-Hu Su, Wei-Hai Fang, Ganglong Cui, and Shaowei Hu
Abstract
The Earth's atmosphere is rich in N2 (78%), but the activation and conversion of nitrogen have been a challenging task due to its chemical inertness. The ammonia industry uses high-temperature and high-pressure conditions to convert N2 and H2 to NH3 on the surface of solid catalysts. Under ambient conditions, certain microorganisms can bind and convert N2 to NH3 via Fe(Mo/V)-based nitrogen fixation enzymes. Although great progress has been made in the structure and intermediates of nitrogen fixation enzymes, the nature of N2 binding to the active site and the detailed mechanism of N2 reduction remains uncertain.
Various studies on the activation of N2 with transition metal complexes have been carried out to better understand the reaction mechanism and to develop catalysts for ammonia synthesis under mild conditions. However, so far, the catalytic conversion of N2 to NH3 by transition metal complexes remains a challenge. Despite the crucial role of vanadium in biological nitrogen fixation, there are few well-defined vanadium complexes that can catalyze the conversion of N2 to NH3. In particular, the V(NxHy) intermediates obtained from the proton/electron transfer reactions of ligated N2 remain unknown.
Herein, this paper reports the vanadium metal complex-catalyzed reduction of nitrogen to ammonia and the first isolation and characterization of a neutral hydrazide complex intermediate ([V]=NNH2) from a nitrogen-activated system, with the cyclic conversion process simulated by the reduction of the protonated vanadium amino complex ([V]-NH2) to obtain a dinitrogen compound and release of ammonia. These findings provide unprecedented insights into the mechanism of N2 reduction associated with FeV nitrogen-fixing enzymes by combining theoretical calculations to elucidate the possible conversion of nitrogen to ammonia via the distal pathway in this catalytic system.
The group of Prof. Dr. Shaowei Hu at Beijing Normal University is dedicated to the development of transition metal complexes for the activation of inert small molecules. Recently, in collaboration with Prof. Dr. Ganglong Cui's group, we reported the reduction of nitrogen to ammonia catalyzed by vanadium metal complexes through a combination of theoretical calculations and experimental studies. The results of this study were published in the Journal of the American Chemical Society, and Wenshang Huang (M.S. student) and Lingya Peng (Ph. D. student) were the co-first authors of this paper, working on the experimental and theoretical calculations, respectively. The study was also strongly supported by Prof. Dr. Weihai Fang from Beijing Normal University, Prof. Dr. Guoyong Song from Beijing Forestry University, and Prof. Dr. Jihu Su from the University of Science and Technology of China.
Synthesis of vanadium metal complex catalysts
A series of dinitrogen complexes with POCOP(2,6-(tBu2PO)2-C6H3) and PCP (2,6-(tBu2-PCH2)2-C6H3) pincer ligands and aromatic oxygen/alkoxy ligands vanadium (3a-e) were synthesized, the pincer complexes are highly reactive in N2 reduction and conversion, while the reduction reaction under argon atmosphere leads to the corresponding divalent compound (4a-e), and the divalent compound can react with nitrogen (high reactivity) to convert to the corresponding dinitrogen complex. The influence of the system solvent, catalyst, proton reagent, and reducing agent on the catalytic reduction reaction was experimentally investigated, and it was found that under certain conditions, the di-nitrogen complex 3b was the most active and could catalyze the reduction conversion of nitrogen to ammonia.
Complex 3b can be converted to the acyl hydrazide complex 5b ([V]=NNH2) by protonation and reduction reactions. Complex 5b can mediate the conversion of 15N2 to 15NH3, indicating that it is a possible catalytic intermediate. Transition metal hydrazide compounds (M=NNH2) are considered to be key intermediates in end-site reaction pathways or mixed (end-site/alternating) type reaction pathways in biological, chemical, and electrochemical nitrogen fixation processes, but the isolation of neutral hydrazide intermediates from nitrogen reduction catalytic systems is challenging, and 5b is the first neutral hydrazide complex isolated from a nitrogen-activated system, and DFT calculations indicate that it has up to 59.1 kcal/mol of N-H bond dissociation free energy (BDFEN-H), which is an important factor for its relatively stable existence.
EPR
The 9.4 GHz powder EPR spectrum obtained at 90 K for 5b shows the V(I = 7/2) center characterized by anisotropic g and A values gx = 1.995, gy = 1.992, gz = 1; Ax = 20 G, Ay = 25 G, and Az = 133.7 G, indicating the dxy ground state spin state (Figure 5). In addition, the two equivalent 31P (I = 1/2) in the liquid and powder EPR spectra are also resolved with an approximately isotropic hyperfine coupling of 21.5G. Possible hyperfine structures from other surrounding nuclei are not resolved. These results suggest that the P-V-P forms a conical structure, consistent with the crystal structure.5b The calculated spin density map shows that the spins are mainly distributed on V (Figure S48), which is consistent with the EPR results.
Mechanism of nitrogen fixation reaction of compound 5b
Conclusion
The results show that transition metal vanadium complexes with POCOP and aryloxy auxiliary ligands can stabilize active nitrogenous species (NHy) and promote the catalytic conversion of N2 to NH3, thus providing more perspectives on the mechanism of biological nitrogen fixation, especially for the mechanism of N2 reduction related to FeV nitrogen fixation enzymes, and providing new ideas for the design of more efficient ammonia synthesis catalysts.
Research Awarded Achievement List - CIQTEK EPR Spectrometer Involved
1. Vanadium-Catalyzed Dinitrogen Reduction to Ammonia via a [V]═NNH2 Intermediate. Journal of the American Chemical Society (2023)
2. Understanding the electro-cocatalytic peroxymonosulfate-based systems with BDD versus DSA anodes: Radical versus nonradical dominated degradation mechanisms. Separation and Purification Technology (2023)
3. Synergistic effect of interstitial C doping and oxygen vacancies on the photoreactivity of TiO2 nanofibers towards CO2 reduction. Applied Catalysis B: Environmental (2022)
4. Dynamic active sites in NiFe oxyhydroxide upon Au nanoparticles decoration for highly efficieMnO2-melittin nanoparticles serve as an effective anti-tumor immunotherapy by enhancing systemic immune responsent electrochemical water oxidation. Nano Energy (2022)
5. Constructing Cu1-Ti dual sites for highly efficient photocatalytic hydrogen evolution. Nano Energy (2022)
6. A Solar-rechargeable Bio-photoelectrochemical System based on Carbon Tracking Strategy for Enhancement of Glucose Electrometabolism. Nano Energy (2022)
7. Enhanced Built‐in Electric Field Promotes Photocatalytic Hydrogen Performance of Polymers Derived from the Introduction of B← N Coordination Bond. Advanced Science (2022)
8. Ex-situ EPR approach to explore the electrochemical behaviour of Arylboron-Linked conjugated microporous polymer cathode. Chemical Engineering Journal (2023)
9. Phosphorus vacancy regulation and interfacial coupling of biotemplate derived CoP@ FeP2 heterostructure to boost pseudocapacitive reaction kinetics. Chemical Engineering Journal (2022)
10. MnO2-melittin nanoparticles serve as an effective anti-tumor immunotherapy by enhancing systemic immune response. Biomaterials (2022)
11. Achieving large thermal hysteresis in an anthracene-based manganese (II) complex via photo-induced electron transfer. Nature Communication (2022)
12. Red-Light-Induced Highly Efficient Aerobic Oxidation of Organoboron Compounds Using Spinach as Photocatalyst. Green Chemistry (2022)
13. Crystal-Facet and Microstructure Engineering in ZnO for Photocatalytic NO Oxidation. Journal of Hazardous Materials (2022)
14. Broad‐Band Visible‐Light Excitable Room‐Temperature Phosphorescence Via Polymer Site‐Isolated Dye Aggregates. Advanced Optical Materials (2022)
15. Construction of a double-walled carbon nanoring. Nanoscale (2021)
16. Design and synthesis of black phosphorus quantum dot sensitized inverse opal TiO2 photonic crystal with outstanding photocatalytic activities. Applied Surface Science (2023)
17. Creation of an internal electric field in SnO2@ZnS-ZnSn(OH)6 dual-type-II heterojunctions for efficient NO photo-oxidation. Science China Materials (2022)
18. Constructing the Multilayer Og-C3N4@ W18O49 Heterostructure for Deeply Photocatalytic Oxidation NO. Separation and Purification Technology (2022)
19. Singlet oxygen-dominated electrocatalytic oxidation treatment for the high-salinity quaternary ammonium compound wastewater with Ti/(RuxIry) O2 anode. Environmental Research (2022)
20. Investigating the transformation and capacitive performance of Al-induced NiCoP nanosheets as an advanced electrode material for supercapacitors. Surfaces and Interfaces (2022)
21. A novel nonmetal intercalated high crystalline g-C3N4 photocatalyst for efficiency enhanced H2 evolution. International Journal of Hydrogen Energy (2022)
22. Interfacial chemical behaviors and petroleum hydrocarbon removal performances of the biochar-mineral composites prepared by one-step pyrolysis. Colloids and Surfaces A: Physicochemical and Engineering Aspects (2022)
23. Photoactive Anthracene-9, 10-dicarboxylic Acid for Tuning of Photochromism in the Cd/Zn Coordination Polymers. Inorganic Chemistry (2022)
24. Large Room Temperature Magnetization Enhancement in a Copper-Based Photoactive Metal–Organic Framework. Inorganic Chemistry (2022)
25. Photochromic Dy-Phosphonate Assembled by a Pyridine Derivative: Synthesis, Structure, and Light-Enhanced Room-Temperature Phosphorescence. Crystal Growth & Design (2022)
26. From Weak to Strong Antiferromagnetism: Tuning the Magnetic Properties of a Mononuclear Fe3+ Complex via Electron Transfer Photochromism. Crystal Growth & Design (2022)
27. Vanadium pentoxide nanosheets with rich oxygen vacancies as a high-performance electrode for supercapacitors. Ionics (2022)
CIQTEK Electron Paramagnetic Resonance (EPR) Spectroscopy
The CIQTEK EPR (ESR) spectroscopy provides a non-destructive analytical method for the direct detection of paramagnetic materials. It can study the composition, structure, and dynamics of magnetic molecules, transition metal ions, rare earth ions, ion clusters, doped materials, defective materials, free radicals, metalloproteins, and other substances containing unpaired electrons, and can provide in situ and non-destructive information on the microscopic scale of electron spins, orbitals, and nuclei. It has a wide range of applications in the fields of physics, chemistry, biology, materials, industry, etc.
