Simulating the synthesis and thermodynamic characteristics of the desolvation of lanthanide borohydride tris-Tetrahydrofuranates

Lanthanide borohydride tris-tetrahydrofuranates (Ln(BH₄) · 3THF, where THF is tetrahydrofuran and Ln is La, Nd, Sm, Gd, Er, Yb, and Lu) is synthesized via the exchange reaction of lanthanide(III) chloride and sodium borohydride in THF. It is found that synthesis proceeds according to a stepwise mechanism and the product of the reaction (lanthanide borohydride) initiates the process. The two-step character of the desolvation of Ln(BH₄)₃ · 3THF under steady-state conditions in the temperature range of 300 to 400 K is determined through X-ray phase and chemical analyses, tensiometry, and gas volumetry. It is established that one mole and then two moles of THF are removed from the initial sample at the first and second steps, respectively. Equations for barograms are obtained and the thermodynamic characteristics of desolvation of Ln(BH₄)₃ · 3THF under study are calculated. Gibbs energy values of the stages of process are determined semi-empirically. The law of its change for the entire series of Ln(BH₄)₃ · 3THF is determined with the emergence of the tetrad effect.     

A Schiff base expanded porphyrin macrocycle that acts as a versatile binucleating ligand for late first-row transition metals

The coordination chemistry of the Schiff base polypyrrolic octaaza macrocycle 1 toward late first-row transition metals was investigated. Binuclear complexes with the divalent cations Ni(II), Cu(II), and Zn(II) and with the monovalent cation Cu(I) were prepared and characterized. Air oxidation of the Cu(I) ions in the latter complex to their divalent oxidation state resulted in a change in the coordination mode relative to the macrocycle.     

System analysis of the thermodynamic properties of binary lanthanide hydrides

Systems analysis of available data on the thermodynamic properties of binary lanthanide hydrides is carried out. The standard thermodynamic characteristics of lanthanide dihydrides (Δ_f H ^o, S ^o, C _p ^o ) and their hypothetical trihydrides (Δ_f H ^o) are calculated. The calculations are performed using a semiempirical method that takes into account the effects of the number of f-shell electrons and the spin and orbital angular moments of ground states of the lanthanide ions on the thermodynamic properties of the compounds studied. It is established that the thermodynamic characteristics of the hydrides exhibit an antibatic behavior with respect to the atomic numbers of the natural series lanthanides. The tetrad effect was revealed for these series of compounds.     

Nonlinear vibrations of an axisymmetric body acted upon by pulse loads

Institute of Mechanics and Seismic Stability of Structures, Tashkent. Translated from Prikladnaya Mekhanika, Vol. 27, No. 4, pp. 68–74, April, 1991.     

Analytical method for parameterizing the random profile components of nanosurfaces imaged by atomic force microscopy

The functional properties of many technological surfaces in biotechnology, electronics, and mechanical engineering depend to a large degree on the individual features of their nanoscale surface texture, which in turn is a function of the surface manufacturing process. Among these features, the surface irregularities and self-similarity structures at different spatial scales, especially in the range of 1 to 100 nm, are of high importance because they greatly affect the surface interaction forces acting at a nanoscale distance. An analytical method for parameterizing the surface irregularities and their correlations in nanosurfaces imaged by atomic force microscopy (AFM) is proposed. In this method, flicker noise spectroscopy--a statistical physics approach--is used to develop six nanometrological parameters characterizing the high-frequency contributions of jump- and spike-like irregularities into the surface texture. These contributions reflect the stochastic processes of anomalous diffusion and inertial effects, respectively, in the process of surface manufacturing. The AFM images of the texture of corrosion-resistant magnetite coatings formed on low-carbon steel in hot nitrate solutions with coating growth promoters at different temperatures are analyzed. It is shown that the parameters characterizing surface spikiness are able to quantify the effect of process temperature on the corrosion resistance of the coatings. It is suggested that these parameters can be used for predicting and characterizing the corrosion-resistant properties of magnetite coatings.     

Self-aligned wet-cell for hydrated microbiology observation in TEM

This paper describes a Self-Aligned Wet (SAW) cell suitable for direct-cell or bacteria incubation and observation in a wet environment inside a transmission electron microscope. This SAW cell is fabricated by a bulk-micromachining process and composed of two structurally complementary counterparts (an out-frame and an in-frame), where each contain a silicon nitride film based observation window. The in- and out-frames can be self-aligned via a mechanism of surface tension from a bio-sample droplet without the aid of positioning stages. The liquid chamber is enclosed between two silicon nitride membranes that are thin enough to allow high energy electrons to penetrate while also sustaining the pressure difference between the TEM vacuum and the vapor pressure within the liquid chamber. A large field of view (150 μm × 150 μm) in a SAW cell is favored and formed from a larger sized observation window in the out-frame, which is fabricated using a unique circular membrane formation process. In this paper, we introduce a novel design to circumvent the challenges of charging/heating problems in silicon nitride that arise from interactions with an electron beam. This paper also demonstrates TEM observations of D. Radiodurans growth in a liquid environment within a thicker chamber (20 μm) within a SAW cell.     

Internal rotation and phase transitions in lanthanum tetrahydroborates

Conclusion The investigation carried out shows that in the low-symmetry compouds La(BH₄)₃ and La(BH₄)₃·3THF, as in the high-symmetry MBH₄, phase transitions occur. An unexpected result is the fact that the symmetry of the environment of the boron ions for these phase transitions practically does not change and remains close to cubic. The activation energy for reorientation of the BH _– ⁴ ion (1.2 kcal/mole) is somewhat overstimated, if we start from the difference in the electronegativity of the boron and hydrogen ions (2.0 and 2.15). This may mean that the nature of the barrier to reorientation of the BH _– ⁴ anion in lanthanum tetrahydroborates is connected with the van der Waals interaction of the tetrahedral BH _– ⁴ groups with the environment. From the¹³⁹La NMR data it follows that the coordination sphere of the triply-charged lanthanum is characterized by low-symmetry of the arrangement of the BH_4– and THF (OC₄H₈) ligands, and the La³⁺-(BH₄)^– bond has predominantly ionic character. Consequently, the potential energy of the BH _– ⁴ anions in the lattice is the sum of the strong isotropic ionic component and the substantially weaker anisotropic van der Waals component. In the low-temperature phases, for both compounds we observe structurally nonequivalent positions for the BH _– ⁴ anions, retained in the high-temperature phase. The phase transitions in the studied compounds are connected with a change in the nature of the hydrogen atom distribution. Due to the low height of the barriers, the reorientational mobility sets in even at low temperatures, and in the phase transition region the value of _c reaches 10¹⁰–10¹¹ Hz. For such a high reorientational frequency, there may be substantial effects from correlation rotation of the anions, leading to a change in the hydrogen atom distribution in the structure and an order-disorder type phase transition.Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 1, pp. 69–72, January–February, 1988.