Digging into the Intrinsic Negative Thermal Expansion of Uranium Tetrafluoride.

The intrinsic negative thermal expansion of UF4 below room temperature was examined. A redetermination of the structure of UF4 by single-crystal X-ray diffraction at 100, 200, and 300 K accompanied by an evaluation of the atomic displacement parameters (ADPs) of the F atoms was performed. The structure of UF4 was described as the stacking of two subnetworks, respectively, constituted by the U(1) and U(2) atoms. The subnetwork formed by the U(2) atoms consists of infinite layers that run parallel to the (b, c) plan. The layers are composed of infinite zigzag chains of corner-sharing U(2)F8 polyhedra running along the c-axis. An increase of temperature from 100 to 300 K leads to a decrease of the unit cell volume and the a and c lattice parameters and an increase of the b lattice parameter. As the temperature increases, the intrachain, interchain, and interlayer U-U distances decrease. It is proposed that the decrease of the intrachain and interlayer U-U distances causes a contraction of the U(2) subnetwork along the a- and c-axis and that a translation of the chains along the c-axis causes an expansion along the b-axis. Analysis of the ADPs of the F atoms indicates that a guitar string effect in the U-F-U units is possibly the origin of the decrease in the U-U distances. A correlation between the U-U distances and the magnitude of the ADPs of the F atoms was established.

Synthesis and Morphological Control of UO2F2 Particulates.

Uranium-based microspheres are of interest due to their potential applications as targets for medical isotopes production, as fuel for nuclear reactors, and as standardized materials for nuclear forensics. Here, for the first time, UO2F2 microspheres (1-2 µm) have been prepared from the reaction between UO3 microspheres and AgHF2 in an autoclave. In this preparation, a new fluorination method has been applied, and HF(g)-produced in situ from the thermal decomposition of AgHF2 and NH4HF2-was used as the fluorinating agent. The microspheres were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Diffraction results indicated that the reaction performed with AgHF2 at 200 °C led to anhydrous UO2F2 microspheres, while at 150 °C, hydrated UO2F2 microspheres were obtained. Meanwhile, NH4HF2 led to the formation of contaminated products as driven by the formation of volatile species.

Synthetic diversity in the preparation of metallic uranium.

Uranium metal is associated with several aspects of nuclear technology; it is used as fuel for research and power reactors, targets for medical isotope productions, explosive for nuclear weapons and precursors in synthetic chemistry. The study of uranium metal at the laboratory scale presents the opportunity to evaluate metallic nuclear fuels, develop new methods for metallic spent fuel reprocessing and advance the science relevant to nuclear forensics and medical isotope production. Since its first isolation in 1841, from the reaction of uranium chloride and potassium metal, uranium metal has been prepared by solid-state reactions and in solution by electrochemical, chemical and radiochemical methods. The present review summarizes the methods outlined above and describes the chemistry associated with each preparation.

Thermal Analysis of Benzotriazolium Perrhenate and Its Implication to Rhenium Metal.

The thermal analysis behavior of C6H6N3[ReO4] was studied by simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) up to 700 °C under argon. Such analysis afforded rhenium metal, which was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. XRD peak broadening due to crystallite size and lattice strain was analyzed by both Williamson-Hall (W-H) and Debye-Scherrer (D-S) methods. Efforts to isolate Re metal from the thermal treatment of benzotriazole (BTA = C6H5N3) with NH4ReO4 and Re2O7 under various atmospheres and temperatures are also reported. The results provide a significant insight into the chemistry of group VII transition metals, investigate the potential use of benzotriazole as a reducing agent for metal productions, and demonstrate a successful convenient method for rhenium metal production, which could be applied to other refractory metals.

Coexistence of metamagnetism and slow relaxation of magnetization in ammonium hexafluoridorhenate.

The (NH4)2[ReF6] (1) salt was studied by X-ray diffraction, Raman spectroscopy, theoretical calculations, and magnetic measurements. 1 crystallizes in the trigonal space group P3̄m1 (Re-F = 1.958(5) Å). In the Raman spectrum of 1, splitting of the observed peaks was observed and correlated to the valence frequencies of vibration of the [ReF6]2- anion. The study of the magnetic properties of 1, through DC and AC magnetic susceptibility measurements, reveals the coexistence of metamagnetism and slow relaxation of magnetization at low temperature, which is unusual in the molecular systems based on the paramagnetic 5d metal ions reported so far.

Coronavirus (COVID-19) and Racial Disparities: a Perspective Analysis.

Health disparity refers to systematic differences in health outcomes between groups and communities based on socioeconomic isolation. In the USA, health disparities among minority groups, especially African Americans, limit their access to quality medical care and other beneficial resources and services. Presently, the novel coronavirus (COVID-19) highlights the extreme healthcare challenges that exist in the African American and other minority communities in the USA. African Americans are dying at a rate nearly four times higher than the national average. With inadequate access to quality healthcare, viable resources, and information, COVID-19 will continue to have a disastrous effect on African American communities. This communication provides a brief overview of the health inequalities resulting in African Americans dying disproportionately during the COVID-19 pandemic.

Coronavirus (COVID-19) in Haiti: A Call for Action.

Recently, the cholera outbreak in Haiti demonstrated just how unprepared the country is to rapidly isolate an outbreak of this magnitude, and its vulnerability to the COVID-19 pandemic. This communication briefly examines the health system in Haiti and its vulnerability toward the COVID-19 outbreak.

An unexpected rhenium(IV)-rhenium(VII) salt: [Co(NH3)6]3[ReVIIO4][ReIVF6]4·6H2O.

The title hydrated salt, tris-[hexa-amminecobalt(III)] tetraoxidorhenate(VII) tetra-kis-[hexa-fluorido-rhenate(IV)] hexa-hydrate, arose unexpectedly due to possible contamination of the K2ReF6 starting material with KReO4. It consists of octa-hedral [Co(NH3)6]3+ cation (Co1 site symmetry 1), tetra-hedral [ReVIIO4]- anions (Re site symmetry 1) and octa-hedral [ReIVF6]2- anions (Re site symmetries 1and ). The [ReF6]2- octa-hedral anions (mean Re-F = 1.834 Å), [Co(NH3)6]3+ octa-hedral cations (mean Co-N = 1.962 Å), and the [ReO4]- tetra-hedral anion (mean Re-O = 1.719 Å) are slightly distorted. A network of N-H⋯F hydrogen bonds consolidates the structure. The crystal studied was refined as a two-component twin.

Syntheses, Raman spectroscopy and crystal structures of alkali hexa-fluorido-rhenates(IV) revisited.

The A2[ReF6] (A = K, Rb and Cs) salts are isotypic and crystallize in the trigonal space group type P [Formula: see text] m1, adopting the K2[GeF6] structure type. Common to all A2[ReF6] structures are slightly distorted octa-hedral [ReF6]2- anions with an average Re-F bond length of 1.951 (8) Å. In those salts, symmetry lowering on the local [ReF6]2- anions from Oh (free anion) to D3d (solid-state structure) occur. The distortions of the [ReF6]2- anions, as observed in their Raman spectra, are correlated to the size of the counter-cations.

Generation of fluorescent silver nanoscale particles in reverse micelles using gamma irradiation.

Reverse micelles (RMs) containing aqueous solutions of Ag(+) ions in their core produce fluorescent Ag species, upon exposure to gamma irradiation. A two-phase liquid system is used for RM formation. The RMs can be employed in novel gamma radiation detectors with appearance of fluorescence indicating that radiation was once present.