Ammonia synthesis activity was improved by high crystallinity CeO₂ covered by low crystallinity CeO₂. However, too much low crystallinity CeO₂ affects ammonia synthesis negatively.

Abstract

Ruthenium (Ru) catalysts supported on cerium oxide (CeO₂), which was composed of high crystallinity (HC) CeO₂ covered by low crystallinity (LC) CeO₂ were investigated. The ammonia synthesis activities of a series of Ru/CeO₂(LC)/CeO₂(HC), having different LC/HC ratios were evaluated, and various characterizations, such as N₂ adsorption, X-ray diffraction, hydrogen temperature-programmed reduction (H₂-TPR), and hydrogen temperature-programmed desorption (H₂-TPD), were performed. Ru/CeO₂(LC)/CeO₂(HC) (0.1) demonstrated higher activity. H₂-TPR revealed that H₂ consumption increased as the LC/HC ratio increased. This indicates that the larger the amount of low crystallinity CeO₂, the higher the reducibility. However, the results of H₂-TPD imply that the larger the amount of low crystallinity CeO₂, the higher the interaction between adsorbed H₂ and the catalyst surface. These results indicate that the balance of reducibility and hydrogen adsorption strength plays an important role in increasing the ammonia synthesis activity.

DFT calculations predict for many cobalt(III) corroles a broken-symmetry open-shell ground state, while CASSCF provides a more nuanced description where the weights of different closed- and open-shell configurations can be obtained. The S−T gap depends on the ligand field produced by the apical ligands and the ease of oxidation of the corroles.

Abstract

Cobalt(III) corroles are the most commonly studied types of metallocorroles, yet the details of their electronic structure, ground spin states and place of redox events are not always straightforward. Corroles are redox active, potentially non-innocent ligands, and it has been found through various experimental and computational techniques, that the innocent or non-innocent behavior is modulated by the apical ligands bound to the cobalt center. In this work, we aim to analyze the effect of corrole substituents and number and type of apical ligands on the electronic structure of cobalt corroles through density functional and wavefunction theories, and to determine the relative energies between closed- and open-shell states. We further perform preliminary analyses on the place of electron abstraction upon oxidation and on the effect of the corrole and apical ligands on the cobalt ligand field splittings. We find that both ligand field and electron-donating or withdrawing effects determine the relative energies of open-shell and closed shell singlet states.

Two novel low-valent Al₃ phosphide clusters exhibiting radical character have been synthesized. Due to pseudo Jahn-Teller effects, the radical is predicted to rapidly interconvert between two low energy states at room temperature.

Abstract

Two novel cyclic Al₃ clusters, Li₂[Al₃(PR₂)₆] ⋅ 2(Et₂O) [R=Ph (1), Cy (2)] were synthesized through salt metathesis of metastable AlCl ⋅ (Et₂O) _n solutions with LiPR₂. Both complexes were characterized by single crystal X-Ray diffraction and their solid state and electronic structures are compared to previously reported cyclic Al₃ clusters. Compounds 1 and 2 were further characterized using density functional theory (DFT) methods to understand the nature of the free electron and the three-center two-electron Al−Al bonds. Calculations revealed that both clusters are influenced by pseudo Jahn-Teller distortion and are likely in equilibrium between two low energy bonding states. The solid-state structures of 1 and 2 are unique among Al₃ clusters, while the electronic structure is similar to the previously reported [Si^t ₄Al₃]. In aluminum chemistry, 1 and 2 are rare examples of clusters containing isoelectronic cores in different ligand environments. The effects of the phosphide ligand sphere and strongly coordinated lithium atoms are discussed in detail.

The Cover Feature shows a virtual factory in which the properties of cobalt corroles can be modulated by appropriate choice of the apical ligands and corrole substituents, which in turn determine the ligand field splitting of the cobalt 3d orbitals and the ease of oxidation of the corrole. Weak axial ligands and electron-donating substituents favour an open-shell singlet ground state while strong axial ligands and electron-withdrawing substituents favour a closed-shell singlet. Density functional and wavefunction theories allow rationalization and prediction of the electronic structure of these complexes. More information can be found in the Research Article by N. I. Neuman.

Two novel nanogels containing Gd(III) or Dy(III) chelates were prepared and proposed as potential candidates for T ₁ and T ₂ MRI contrast agents. These samples exhibit remarkable chemical stability in biological fluids and demonstrate enhanced longitudinal and transverse relaxivity and MRI contrast when compared to commercially available probes, particularly at high magnetic field strengths.

Abstract

Novel nanogels, characterized by high stability and incorporating macrocyclic chelates of Gd(III) and Dy(III), were synthesized and assessed for their effectiveness as T ₁ and T ₂ relaxation agents, respectively. In this specific design, we employed octacoordinated bifunctional Gd-1,7-DOTAGA₂ chelate to cross-link chitosan chains. The results revealed that the sample exhibited a relaxivity value at clinical magnetic field strengths (1.5 T), approximately seven times higher than that of currently available clinical contrast agents and good MRI contrast efficacy at both 7.1 and 1 T. Furthermore, the nanogel displayed excellent stability in biological fluids, with no discernible interactions with serum biomolecules and no release of metal. In addition to Gd(III)-based probes commonly used as T ₁ positive contrast agents, the nanogel with the corresponding Dy-1,7-DOTAGA₂ chelate was prepared to explore its potential as a T ₂ MRI probe. Dy-based nanogel demonstrated notably elevated transverse relaxivity values compared to the free chelate at high magnetic fields (>3 T) and significant T ₂ MRI contrast at 7.1 T, a capability often lacking when employing an equivalent concentration of a low-molecular-weight Dy(III) complex. The characterization of paramagnetic complexes was completed through the measurement of ¹H NMRD profiles and ¹⁷O NMR data.

The optimized Ni/NiO-NFs catalyst shows 100% AB dehydrogenation within 5 min, and a r_B value of 2917 ml min⁻¹ g_Ni ⁻¹ and a low activation energy 48.1 KJ/mol at 298 K.

Abstract

Clean and sustainable hydrogen production through liquid hydrogen storage material requires highly active and stable earth-abundant non-noble metal to replace expensive and rare noble metals. Herein, nickel nanofilms (Ni/NiO-NFs) were prepared by the ionic liquid/water interface route. The cationic carbon chain length of the ionic liquid affects the phase composition of the nickel nanofilm, and the ionic liquid with [OMIm][PF₆] as the anion has good thermal stability during the synthesis process. The efficiency of Ni/NiO-NFs catalysts was tested by comparative kinetic analysis of the AB hydrolysis for hydrogen production. The as-prepared Ni/NiO-NFs catalyst exhibits excellent hydrogen generation performances, including a hydrogen production rate (2917 ml min⁻¹ g_Ni ⁻¹), and a low activation energy (48.1 kJ/mol). The transition of nickel oxide to metallic nickel and the destruction of the catalyst structure is responsible for the decreased durability. This work highlights the significance of amorphous nanofilms catalysts via the ionic interface method on the regulation of activity for AB hydrolysis.

1,3,4,4-Tetrapiperidino-1,2-cyclobutadiene-iridium complexes [(CBA)IrL(COD)] with a four-membered cyclic bent allene (CBA) ligand have been prepared by cyclization of 1,3,4,4-tetrapiperidino-1,3-butenyne with [IrCl(COD)]₂, followed by chloride abstraction and substitution with phosphines and pyridine, respectively. The reaction of [(CBA)IrCl(COD)] with carbon monoxide afforded the dicarbonyl complex cis-[(CBA)IrCl(CO)₂], which exhibits very low CO stretching frequencies, emphasizing the outstanding donor ability of the CBA ligand.

Abstract

The dimer of dipiperidinoacetylene, 1,3,4,4-tetrapiperidino-3-buten-1-yne, reacts with [IrCl(COD)]₂ (COD=1,5-cyclooctadiene) to give the corresponding 1,3,4,4-tetrapiperidino-1,2-cyclobutadiene-iridium complex [(CBA)IrCl(COD)] with a four-membered cyclic bent allene (CBA) ligand. Reaction with carbon monoxide affords the dicarbonyl complex cis-[(CBA)IrCl(CO)₂], which exhibits low CO stretching frequencies and an associated Tolman electronic parameter (TEP) value of 2030 cm⁻¹, which is lower than any other TEP value reported for cyclic carbene and carbenoid ligand systems. Treatment of [(CBA)IrCl(COD)] with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBARF) followed by addition of phosphines or pyridine (py) yields the cationic complexes [(CBA)IrL(COD)][BARF] (L=PPh₃, PPh₂Me, PPhMe₂, PCy₃, py) as potential hydrogen isotope exchange (HIE) catalysts. DFT calculations provide evidence for a suitable pathway for the cyclization of 1,3,4,4-tetrapiperidino-3-buten-1-yne at transition metal complex fragments, here AuCl, IrCl(COD), and IrCl(CO)₂, as a general route to four-membered CBA metal complexes.

We are reporting the crystal structure of the tetrabutylammonium (TBA) salt of the old Co(II) Keggin phosphotungstate anion (Co(II)POM) and a study of the magnetic behaviour of this well-known POM. It behaves as a field-induced single ion magnet (SIM) showing slow relaxing magnetization below 5 K under small DC applied magnetic fields. Raman relaxation mechanisms dominates with different relaxation times observed when switching from the TBA salt to the K salt of the Co(II)POM.

Abstract

We are reporting the single crystal structure of the tetrabutylammonium (TBA) salt of the old Co(II) Keggin phosphotungstate anion (Co(II)POM) and a study of the magnetic behaviour of this well-known POM. This Co(II)POM crystallizes in a cubic cell and this high symmetry obscure a precise characterization of Co(II) coordination sphere metrics due to positional disordered. We employed DFT and SA-SOC-CASSCF as auxiliary tools to complement DC and AC magnetic data collected. The studied complex behaves as a field-induced single ion magnet (SIM) showing slow relaxing magnetization below 5 K under small DC applied magnetic fields. Raman relaxation mechanisms dominates with different relaxation times observed when switching from the TBA salt to the K salt of the Co(II)POM.