Inorganic Chemistry最新文献

We report the structural defects in Zr-metal-organic framework (MOFs) for achieving highly efficient CO₂ reduction under visible light irradiation. A series of defective Zr-MOF-X (X = 160, 240, 320, or 400) are synthesized by acid-regulated defect engineering. Compared to pristine defect-free Zr-MOF (NNU-28), N₂ uptake increases for Zr-MOF-X synthesized with the HAc modulator, producing a larger pore space and Brunauer-Emmett-Teller surface area. The pore size distribution demonstrates that defective Zr-MOF-X exhibits mesoporous structures. Electrochemistry tests show that defective Zr-MOF-X possesses a more negative reduction potential and a higher photocurrent responsive signal than that of pristine NNU-28. Consequently, the defective samples exhibit a significantly higher efficiency in the photoreduction of CO₂ to formate. Transient absorption spectroscopies manifest that structural defects modulate the excited-state behivior of Zr-MOF-X and improve the photogenerated charge separation of Zr-MOF-X. Furthermore, electron paramagnetic resonance and in-suit X-ray photoelectron spectroscopy provide additional evidence of the high photocatalytic performance exhibited by defective Zr-MOF-X. Results demonstrate that structural defects in Zr-MOF-X also improve the charge transfer, producing abundant Zr(III) catalytically active sites, exhibiting a slower decay process than defect-free Zr-MOF. The long-lifetime Zr(III) species in defective Zr-MOF-X are fully exposed to a high-concentration CO₂ atmosphere, thereby enhancing the photocatalytic efficiency of CO₂ reduction.

Designing and synthesizing hollow frame structures with unique three-dimensional open structures in electrocatalysis remain a challenge. Etching is an effective method to synthesize metal-organic frameworks (MOFs) with a hollow structure and rich function. Herein, we report the design and synthesis of Hf-doped CoP hollow nanocubes by selective etching and ion exchange. Different from the traditional etching method, we used acid xylenol orange solution to etch typically the (211) crystal face of ZIF-67, obtaining the unique bell-like structure, named XO-ZIF-67. Subsequently, Hf-doped CoP hollow nanocubes were formed by Hf⁴⁺ doping and simple phosphating treatment. Electrochemical tests showed that the overpotential of the obtained catalyst is only 291 mV at the current density of 10 mA cm^-2 when applied in catalyzing the oxygen evolution reaction (OER). Furthermore, the catalyst shows excellent stability when running in 1 M KOH solution for 25 h.

An efficient method for the selective conversion of glycerol, the major byproduct of the biodiesel manufacturing process, to lactic acid in water via acceptorless dehydrogenation has been developed. In the presence of a water-soluble [Cp*Ir(6,6'-(OH)₂-2,2'-bpy)(H₂O)][OTf]₂ (0.1 mol %) and KOH (1.1 equiv), the reaction proceeded at 120 °C for 24 h to afford the desired product in >99% yield with >99% selectivity. It was confirmed that OH functional groups in the ligand were crucial for the activity of the iridium complex. Furthermore, density functional theory calculations and mechanistic experiments were also undertaken.

2,2'-Bipyridyl (bpy) is widely used as a chelating unit for metal complexation but is not usually considered as a hydrogen-bonding unit. This is because the metal-free bpy units are usually in a transoid conformation, and the two nitrogen lone pairs are pointed to the opposite sides. We now report a metallomacrocycle whose three metal-free bpy units are in a cisoid conformation and are fixed in the cavity. The complexation of nickel(II) only at the salen units of the triangular bpytrisalen ligand produced this rigid and planar macrocycle. Its cavity is surrounded by hydrogen-bond acceptors (N of bpy and O of salen), and it was found that unique pentagonal prism clusters of water molecules templated by the cavity were formed in the crystal. This study has not only increased the variation of the synthetic methodologies of multinuclear complexes but has also provided the structural platform on which multiple bpy units exert hydrogen-bonding functions.

In recent years, halide perovskites have attracted considerable attention for photocatalytic CO₂ reduction. However, the presence of surface defects and the lack of specific catalytic sites for CO₂ reduction lead to low photocatalytic performance. In this study, we demonstrate a facile method that post-treats CsPbBr₃ with ZnBr₂ for photocatalytic CO₂ reduction. Our experimental and characterization results show that ZnBr₂ has a dual role: the Br^- ions in ZnBr₂ passivate Br vacancies (V_Br) on the CsPbBr₃ surface, while Zn²⁺ cations act as catalytic sites for CO₂ reduction. The ZnBr₂-CsPbBr₃ achieves a photocatalytic CO evolution rate of 57 μmol g^-1 h^-1, which is nearly three times higher than that of the pristine CsPbBr₃. The enhanced performance over ZnBr₂-CsPbBr₃ is mainly due to the decreased V_Br and lower reaction energy barrier for CO₂ reduction. This work presents an effective method to simultaneously passivate surface defects and introduce catalytic sites, providing useful guidance for the regulation of perovskite photoelectric properties and the design of efficient photocatalysts.

Actinide +IV complexes with six nitrates [An^IV(NO₃)₆]^2- (An = Th, U, Np, and Pu) have been studied by ¹⁵N and ¹⁷O NMR spectroscopy in solution and first-principles calculations. Magnetic susceptibilities were evaluated experimentally using the Evans method and are in good agreement with the ab initio values. The evolution in the series of the crystal field parameters deduced from ab initio calculations is discussed. The NMR paramagnetic shifts are analyzed based on ab initio calculations. Because the cubic symmetry of the complex quenches the dipolar contribution, they are only of Fermi contact origin. They are evaluated from first-principles based on a complete active space/density functional theory (DFT) strategy, in good accordance with the experimental one. The ligand hyperfine coupling constants are deduced from paramagnetic shifts and calculated using unrestricted DFT. The latter are decomposed in terms of the contribution of molecular orbitals. It highlights two pathways for the delocalization of the spin density from the metallic open-shell 5f orbitals to the NMR active nuclei, either through the valence 5f hybridized with 6d to the valence 2p molecular orbitals of the ligands, or by spin polarization of the metallic 6p orbitals which interact with the 2s-based molecular orbitals of the ligands.

The effects of simulated radiolytic degradation of tri-n-butyl phosphate (TBP) on the chemical speciation of cerium were studied by spectrophotometry and electrochemistry of TBP solutions containing increasing amounts of di-n-butyl phosphoric acid (HDBP), a common degradation product of TBP. Tetravalent cerium was found to exchange coordinated nitrate for the dibutyl phosphate anion, forming dinuclear complexes of the formula (CeOCe)(NO₃)_(6-d)(DBP)_d·3TBP (d = 0-3). Compared to Ce(IV), Ce(III) was complexed less strongly by HDBP in TBP, but HDBP displaced both nitrate and TBP to form the series of mononuclear complexes Ce(NO₃)_(3-d)(HDBP·DBP)_d·(3-d)TBP (d = 0-3). Dibutyl phosphate coordination caused large negative shifts in the Ce(IV/III) reduction potential in TBP, indicating a strong stabilization of the tetravalent state. Electrochemical investigation of the reduction of Ce(IV) in TBP revealed it to be a two-electron process in accordance with the dinuclear nature of the organic-phase Ce(IV) complexes. The diffusion coefficients of the d = 0 dinuclear Ce(IV)-nitrate-TBP complex and mononuclear Ce(III)-nitrate-TBP complex in TBP equilibrated with 7 M HNO₃ were determined to be (1.16 ± 0.06) × 10^-7 cm²/s and (1.9 ± 0.4) × 10^-7 cm²/s, respectively, which also is consistent with the larger molecular volume of the dinuclear Ce(IV) complexes.