Inorganics, Volume 9, Issue 5 (May 2021) – 11 articles

Nanocrystals of gadolinium orthoferrite (GdFeO₃) with morphology close to isometric and superparamagnetic behavior were successfully synthesized using direct, reverse and microreactor co-precipitation of gadolinium and iron(III) hydroxides with their subsequent heat treatment in the air. The obtained samples were investigated by PXRD, FTIR, low-temperature nitrogen adsorption-desorption measurements, HRTEM, SAED, DRS and vibration magnetometry. According to the X-ray diffraction patterns, the GdFeO₃ nanocrystals obtained using direct co-precipitation have the smallest average size, while the GdFeO₃ nanocrystals obtained using reverse and microreactor co-precipitation have approximately the same average size. It was shown that the characteristic particle size values are much larger than the corresponding values of the average crystallite size, which indicates the aggregation of the obtained GdFeO₃ nanocrystals. The GdFeO₃ nanocrystals obtained using direct co-precipitation aggregate more than the GdFeO₃ nanocrystals obtained using reverse co-precipitation, which, in turn, tend to aggregate more strongly than the GdFeO₃ nanocrystals obtained using microreactor co-precipitation. The bandgap of the obtained GdFeO₃ nanocrystals decreases with decreasing crystallite size, which is apparently due to their aggregation. The colloidal solutions of the obtained GdFeO₃ nanocrystals with different concentrations were investigated by ¹H NMR to measure the T₁ and T₂ relaxation times. Based on the obtained r₂/r₁ ratios, the GdFeO₃ nanocrystals obtained using microreactor, direct and reverse co-precipitation may be classified as T₁, T₂ and T₁–T₂ dual-modal MRI contrast agents, respectively. Full article

The reaction of ammoniacal AgNO₃ solution (or aq. solution of [Ag(NH₃)₂]NO₃) with aq. NaClO₄ resulted in [Ag(NH₃)₂]ClO₄ (compound 1). Detailed spectroscopic (correlation analysis, IR, Raman, and UV) analyses were performed on [Ag(NH₃)₂]ClO₄. The temperature and enthalpy of phase change for compound 1 were determined to be 225.7 K and 103.04 kJ/mol, respectively. We found the thermal decomposition of [Ag(NH₃)₂]ClO₄ involves a solid-phase quasi-intramolecular redox reaction between the perchlorate anion and ammonia ligand, resulting in lower valence chlorine oxyacid (chlorite, chlorate) components. We did not detect thermal ammonia loss during the formation of AgClO₄. However, a redox reaction between the ammonia and perchlorate ion resulted in intermediates containing chlorate/chlorite, which disproportionated (either in the solid phase or in aqueous solutions after the dissolution of these decomposition intermediates in water) into AgCl and silver perchlorate. We propose that the solid phase AgCl-AgClO₄ mixture eutectically melts, and the resulting AgClO₄ decomposes in this melt into AgCl and O₂. Thus, the final product of decomposition is AgCl, N₂, and H₂O. The intermediate (chlorite, chlorate) phases were identified by IR, XPS, and titrimetric methods. Full article

As the world evolves, so does the energy demand. The storage of hydrogen using metal hydrides shows great promise due to the ability to store and deliver energy on demand while achieving higher volumetric density and safer storage conditions compared with traditional storage options such as compressed gas or liquid hydrogen. Research is typically performed on lab-sized samples and tanks and shows great potential for large scale applications. However, the effects of scale-up on the metal hydride’s performance are relatively less investigated. Studies performed so far on both materials, and hydride-based storage tanks show that the scale-up can significantly impact the system’s capacity, kinetics, and sorption properties. The findings presented in this review suggest areas of further investigation in order to implement metal hydrides in real scale applications. Full article

Magnesium-based hydrides are considered as promising candidates for solid-state hydrogen storage and thermal energy storage, due to their high hydrogen capacity, reversibility, and elemental abundance of Mg. To improve the sluggish kinetics of MgH₂, catalytic doping using Ti-based catalysts is regarded as an effective approach to enhance Mg-based materials. In the past decades, Ti-based additives, as one of the important groups of catalysts, have received intensive endeavors towards the understanding of the fundamental principle of catalysis for the Mg-H₂ reaction. In this review, we start with the introduction of fundamental features of magnesium hydride and then summarize the recent advances of Ti-based additive doped MgH₂ materials. The roles of Ti-based catalysts in various categories of elemental metals, hydrides, oxides, halides, and intermetallic compounds were overviewed. Particularly, the kinetic mechanisms are discussed in detail. Moreover, the remaining challenges and future perspectives of Mg-based hydrides are discussed. Full article

A new mixed alkali metal–aluminum borohydride LiAl(BH₄)₂Cl₂ has been prepared via mechanochemical synthesis from the 2LiBH₄–AlCl₃ mixture. Structural characterization, performed using a combination of X-ray powder diffraction and solid-state NMR methods, indicates that the LiAl(BH₄)₂Cl₂ phase adopts a unique 3D framework and crystallizes in an orthorhombic structure with the space group C222₁, a = 11.6709(6) Å, b = 8.4718(4) Å, c = 7.5114(3) Å. The material shows excellent dehydrogenation characteristics, where hydrogen evolution starts at Tons = 70 °C, releasing approximately 2 wt.% of nearly pure (99.8 vol.%) hydrogen and a very small amount (~0.2 vol.%) of diborane. When compared to halide-free mixed alkali metal–aluminum borohydrides, the presence of Al‒Cl bonding in the LiAl(BH₄)₂Cl₂ structure likely prevents the formation of Al(BH₄)₃ upon decomposition, thus suppressing the formation of diborane. Full article

Mono- and binuclear arene–ruthenium(II) complexes with imidazole-containing ligands were prepared by the reaction of the ligands (L¹ = bis(imidazole-1-yl)methane; ImH = 1H-Imidazole; BImH = 1H-Benzimidazole) with [(p-cym)Ru(µ-Cl)₂]₂ dimers. When bis(imidazole-1-yl)methane reacted with [(p-cym)Ru(µ-Cl)₂]₂ in methanol, a binuclear complex of the type [Ru₂(L¹)₂(p-cym)₂Cl₂]Cl₂ (2) with cyclic structure was synthesized, whereas by using acetonitrile as a solvent under the same reaction conditions, an unexpected C–N bond cleavage was observed, and a complex of formula [Ru(ImH)₂(p-cym)Cl]Cl (1) with coordinated imidazole molecules was obtained. Another type of arene–ruthenium complex [Ru(BImH)(p-cym)Cl₂] (3) was obtained by the reaction of benzimidazole and [(p-cym)Ru(µ-Cl)₂]₂. All compounds were characterized by spectral (FT-IR, NMR ¹H, ¹³C) and single-crystal X-ray diffraction methods; their catalytic activity in transfer hydrogenation and the cytotoxicity against MCF-7 and HepG2 cells were evaluated. Full article

Metal–Organic Frameworks (MOFs) and Coordination Polymers (CPs) are at the forefront of contemporary coordination chemistry research, as witnessed by the impressive (and ever-growing) number of publications appearing in the literature on this topic in the last 20 years (Figure 1), reaching almost 4000 papers in 2020 [...] Full article

The development of supramolecular systems showing aurophilic interactions in solution is gaining much attention in the last years. This is due to the intriguing photophysical properties of gold(I) complexes, which usually confer to these supramolecular assemblies interesting luminescent properties, as well as the possibility of morphological modulation, through fine tuning of inter- and intramolecular aurophilic interactions, in synergy with the formation of other supramolecular contacts. In this work, an overview of the advances made in this area since 2015 is presented. A large variety of systems showing different spectroscopical and structural topologies has been reported. Moreover, these supramolecular assemblies have proven to be useful in a wide range of applications. Full article

Information resulting from a comprehensive investigation into the intrinsic strengths of hydrated divalent magnesium clusters is useful for elucidating the role of aqueous solvents on the Mg²⁺ ion, which can be related to those in bulk aqueous solution. However, the intrinsic Mg–O and intermolecular hydrogen bond interactions of hydrated magnesium ion clusters have yet to be quantitatively measured. In this work, we investigated a set of 17 hydrated divalent magnesium clusters by means of local vibrational mode force constants calculated at the $\omega$B97X-D/6-311++G(d,p) level of theory, where the nature of the ion–solvent and solvent–solvent interactions were interpreted from topological electron density analysis and natural population analysis. We found the intrinsic strength of inner shell Mg–O interactions for [Mg(H₂O)_n]²⁺ (n = 1–6) clusters to relate to the electron density at the bond critical point in Mg–O bonds. From the application of a secondary hydration shell to [Mg(H₂O)_n]²⁺ (n = 5–6) clusters, stronger Mg–O interactions were observed to correspond to larger instances of charge transfer between the lp(O) orbitals of the inner hydration shell and the unfilled valence shell of Mg. As the charge transfer between water molecules of the first and second solvent shell increased, so did the strength of their intermolecular hydrogen bonds (HBs). Cumulative local vibrational mode force constants of explicitly solvated Mg²⁺, having an outer hydration shell, reveal a CN of 5, rather than a CN of 6, to yield slightly more stable configurations in some instances. However, the cumulative local mode stretching force constants of implicitly solvated Mg²⁺ show the six-coordinated cluster to be the most stable. These results show that such intrinsic bond strength measures for Mg–O and HBs offer an effective way for determining the coordination number of hydrated magnesium ion clusters. Full article

Separate reactions of [Th{N(CH₂CH₂NSiMe₂Bu^t)₂(CH₂CH₂NSi(Me)(Bu^t)(μ-CH₂)]₂ (1) with [Re(η⁵-C₅H₅)₂(H)] (2) or [Ru(η⁵-C₅H₅)(H)(CO)₂] (3) produced, by alkane elimination, [Th(Tren^DMBS)Re(η⁵-C₅H₅)₂] (ThRe, Tren^DMBS = {N(CH₂CH₂NSiMe₂Bu^t)₃}^3-), and [Th(Tren^DMBS)Ru(η⁵-C₅H₅)(CO)₂] (ThRu), which were isolated in crystalline yields of 71% and 62%, respectively. Complex ThRe is the first example of a molecular Th-Re bond to be structurally characterised, and ThRu is only the second example of a structurally authenticated Th-Ru bond. By comparison to isostructural U-analogues, quantum chemical calculations, which are validated by IR and Raman spectroscopic data, suggest that the Th-Re and Th-Ru bonds reported here are more ionic than the corresponding U-Re and U-Ru bonds. Full article

The anharmonic phonon behavior in zirconium hydrides and deuterides, including ϵ-ZrH₂, γ-ZrH, and γ-ZrD, has been investigated from aspects of inelastic neutron scattering (INS) and lattice dynamics calculations within the framework of density functional theory (DFT). The harmonic model failed to reproduce the spectral features observed in the experimental data, indicating the existence of anharmonicity in those materials and the necessity of further explanations. Here, we present a detailed study on the anharmonicity in zirconium hydrides/deuterides by exploring the 2D potential energy surface of hydrogen/deuterium atoms and solving the corresponding 2D single-particle Schrödinger equation to obtain the eigenfrequencies, which are then convoluted with the instrument resolution. The convoluted INS spectra qualitatively describe the anharmonic peaks in the experimental INS spectra and demonstrate that the anharmonicity originates from the deviations of hydrogen potentials from quadratic behavior in certain directions; the effects are apparent for the higher-order excited vibrational states, but small for the ground and first excited states. Full article