A series of substituted ferrocenyl boranes and boronic acids were synthesized. The oxidation to the corresponding ferrocenium derivatives provides access to strong Lewis acids as characterized by computational methods. The ferrocenium derivatives were active catalysts for the Lewis acid mediated Meinwald epoxide rearrangement and yielded predominantly the aldehydes as kinetic products.

Abstract

A series of substituted ferrocenyl boron derivatives was synthesized. The oxidation of the ferrocenyl unit resulted in a significant increase of the boron-centered Lewis acidity. The neutral and cationic Lewis acids were characterized by NMR spectroscopy, crystal structure analysis and by computational methods. The new Lewis acids were then applied in the Meinwald rearrangement of epoxides, predominantly furnishing aldehydes as the kinetic products.

The bigger siblings of the triflate anion, namely the trichlate [Cl₃CSO₃]⁻ and the tribrate [Br₃CSO₃]⁻ are synthesized as their lithium salts. The compounds display molecular structures with the anions, the lithium cations and water molecules arranged into dimers [Li₂(X₃CSO₃)₂(H₂O)₄] (X=Cl, Br). The figure shows both dimers, partly in an ORTEP style and partly as a Lewis formula.

Abstract

Lithium trichlate, Li[Cl₃CSO₃] ⋅ 2H₂O (triclinic, , Z=2, a=630.29(3) pm, b=630.65(3) pm, c=1246.10(6) pm, α=100.657(2)°, β=97.813(2)°, γ=107.994(2)°) was obtained from the reaction of (H₅O₂)[Cl₃CSO₃] and LiOH in aqueous solution. Similarly, colourless single crystals of the tribrate Li[Br₃CSO₃] ⋅ 2H₂O (triclinic, , Z=4, a=634.65(4) pm, b=636.83(4) pm, c=2496.8(2) pm, α=83.518°, β=86.081(5)°, γ=72.061(5)°) form in the reaction of aqueous Br₃CSO₃H and LiOH. The acid (H₅O₂)[Cl₃CSO₃] was obtained from the chlorination of CS₂, followed by oxidation of the intermediate Cl₃CSCl with H₂O₂. The bromo derivative Br₃CSO₃H has been prepared by bromination of phenylsulfonate with KOBr and subsequent ion exchange of the obtained potassium salt. Both lithium compounds exhibit molecular dimers according to {Li₂(X₃CSO₃)_2/1(H₂O)_2/1(H₂O)_2/2} with the Li⁺ ions in tetrahedral coordination of oxygen atoms. The difference in the crystal structures result from the variation of the orientation of the dimers with respect to each other. The experimental findings for the dimers are in good agreement with DFT calculations.

Three new solvent adducts [Mn(sal-N-1,5,8,12)]I⋅CH₃OH, [Mn(sal-N-1,5,8,12)]I⋅C₂H₅OH and [Mn(sal-N-1,5,8,12)]I⋅CH₃CN, as well as a rare compound, [Mn(sal-N-1,5,8,12)]I₃ are synthesized. Surprisingly, the solvent in compound [Mn(sal-N-1,5,8,12)]I⋅CH₃OH easily escapes, and with a slight increase in temperature, the crystal collapses, eventually turning into a powdered state. The magnetic properties undergo significant changes accompanying the loss of the solvent.

Abstract

The interplay of host-guest interactions and controlled modulation of spin-crossover (SCO) behavior is one of the most exploited topics regarding data storage, molecular sensing, and optical technologies. This study examines the effect of solvents on the spin-crossover (SCO) behavior of manganese(III) complexes [Mn(sal-N-1,5,8,12)]I•S (S=CH₃OH, C₂H₅OH, CH₃CN) (1) and [Mn(sal-N-1,5,8,12)]I₃ (2), where (sal-N-1,5,8,12)²⁻ is 2,2′-((1E,13E)-2,6,9,13-tetraazatetradeca-1,13-diene-1,14-diyl)diphenol synthesized by salicylaldehyde and 1,2-bis(3-aminopropylamino)ethane. The complexes, crystallizing in orthorhombic or monoclinic systems, exhibit similar supramolecular arrangements with one-dimensional cationic chains at low temperatures. Magnetic studies reveal that solvent inclusion sharpens the SCO transition and lowers the transition temperature. Specifically, 1⋅CH₃OH shows a 13 K thermal hysteresis due to methanol‘s mobility through the channels in the cationic framework. Although the solvent-free compound was not obtained, compound 2 with a linear I₃ ⁻ anion was synthesized, displaying extensive cation-anion contacts and a distinct 13 K thermal hysteresis upon heating due to altered intermolecular cooperativity. This emphasizes the significant role of solvent introduction and variation in crystal packing and their impact on the SCO properties.

Molecular systems, including homogeneous transition metals complexes and those of main group elements, are examined to illustrate the various types of stoichiometric N−H bond cleavage reactions. Molecular complexes that mediate catalytic NH₃ oxidation to N₂ through chemically or electrochemically driven reactions are described.

Abstract

The molecular complexes described herein use main-group elements or transition metals to control the stoichiometric cleavage of N−H bonds of ammonia (NH₃) and/or catalyze chemical and electrochemical NH₃ oxidation to dinitrogen (N₂). We highlight the phenomenon of coordination-induced bond weakening and a variety of N−H bond cleavage mechanisms of NH₃ including H atom abstraction, inter- and intra-molecular deprotonation reactions, oxidative addition, and σ -bond metathesis that have been demonstrated with molecular systems. We provide an overview of the molecular complexes reported for the rapidly developing field of NH₃ oxidation catalysis to form N₂. These systems exhibit several diverse structure types and innovative ligands to support transition metals capable of activating NH₃ and mediating a challenging chemical transformation that requires breaking strong N−H bonds and forming an N−N bond en route to N₂ formation.

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.

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.

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.

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 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 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.