Chemical Oxygen Demand

New instrumental methods and tendencies of development of direct potentiometric determination of the chemical oxygen demand in the framework of the standard technique are considered.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 1, 2005, pp. 102–107.Original Russian Text Copyright © 2005 by Pisarevsky, Polozova, Hockridge.     

Tantalum(v) oxoalkoxides. Synthesis and structure

Anodic oxidation of tantalum in isopropyl alcohol or prolonged reflux of an alcohol solution of Ta(OPrⁱ)₅ afford crystalline oxoisopropoxide Ta₂O(OPrⁱ)₈ · PrⁱOH (1). In its molecule, two octahedra about Ta atoms are linkedvia the shared edge [(OPrⁱ)O]. Compound1 is the first example of oxoalkoxide containing such a small number of metal atoms. Unlike the known polynuclear molecules M _n O _m (OR) _p , oxoalkoxide1 is stable in solutions; on transition to the gas phase, this compound is desolvated to form a very stable molecule Ta₂O(OPrⁱ)₈ (apparently, consisting of two octahedra with a shared edge). According to the data of mass spectrometry, analogous molecules exist in the gas phase over Ta(OAlk)₅ (Alk = Me, Et, Prⁱ, or Bu¹¹). When compound1 is heated invacuo (10^–2–10^–3 Torr), Ta(OPrⁱ)₅ is sublimated. Crystals of Ta₇O₉(OPrⁱ)₁₇ (2) were formed upon prolonged storage of solutions of1 in PrⁱOH. Heptanuclear molecule2 consists of two [Ta₄] tetrahedra with a shared vertex. These tetrahedra are additionally linked togethervia one ₃-oxo and two ₂-OPrⁱ groups. Complex2 is a representative of heptameric oxoalkoxides of a new structural type.Deceased in I995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–131, January, 1996.     

Rearrangement of the Structure of Paratellurite Crystals in a Near-Surface Layer Caused by the Migration of Charge Carriers in an External Electric Field

The process of formation of surface structures in a paratellurite crystal (α-TeO₂) in an external electric field has been studied by in situ X-ray diffraction (XRD) measurements. This process is reversible and its dynamics (duration of tens of minutes) corresponds to the formation of a screening layer near the insulator–metal interface owing to the counter migration of oxygen ions and vacancies in the external electric field. The formation of domains has been observed in the experiment as the broadening and splitting of the XRD curve and is explained by mechanical stresses that appear in the high electric field near the surface in view of the piezoelectric effect and are responsible for a ferroelectric α–β phase transition. A change in the lattice parameter near the anode (surface of the crystal with a positive external charge) has been detected simultaneously. This change is due to the local rearrangement of the crystal structure because of the inflow of oxygen ions in this region and outflow of oxygen vacancies.     

Investigation of the Structure of Crystal-Forming Solutions of Potassium Dihydrogen Phosphate K(H2PO4) (KDP type) on the Basis of Modeling Precursor Clusters and According to Small-Angle X-Ray Scattering Data

Crystallography Reports - The potassium dihydrogen phosphate K(H2PO4) (KDP) cluster structures formed in aqueous solutions have been theoretically and experimentally investigated. Cluster modeling...     

Interaction ofZ-1,2-borylphosphinoalkene with ketenimine

N-Phenyl-C,C-diphenylketenimine adds toZ-1-butyl-I-dibutylboryl-2-diphenylphosphino-2-phenylethene to give 2,2,3-tributyl-6-diphenylmethylideno-1,4,5,5-tetraphenyl-1-aza-5-phosphonia-2-borataeyclohex-3-ene, which rearranges into 4,6-dibutyl-2-diphenylphosphino-1,1,3,5-tetraplienyl-3-aza-4-boradeca-1,5-diene upon heating. Its crystal structure has been established by X-ray analysis.Deceased in 1995.Translated from IIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. l, pp. 183–187, January, 1996.     

Small-angle X-ray scattering study of conditions for the formation of growth units of protein crystals in lysozyme solutions

The structural composition of lysozyme solutions favorable for the formation of the tetragonal form of protein crystals was studied by synchrotron-based small-angle X-ray scattering depending on the protein concentration and the temperature. Along with lysozyme monomers, dimers and octamers are found in crystallization solutions; the octamer content increases with an increase in the protein concentration.     

Erratum to:Influence of Chlorides of Mono- and Divalent Metals on the Oligomeric Composition of Lysozyme Crystallization Solutions and Further Crystal Growth

Crystallography Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S1063774521340046     

X-ray Diffraction Analysis of the Structure In0.53Ga0.47As Films Grown on (100) and (111)A GaAs Substrates with a Metamorphic Buffer

Crystallography Reports - Epitaxial In0.53Ga0.47As films, grown on GaAs substrates with the (100) and (111)А crystallographic orientations in the standard high-temperature and low-temperature...     

Accurate Crystal Structure Refinement of La3Ta0.25Zr0.50Ga5.25O14

Crystallography Reports - An accurate X-ray diffraction study of a La3Ta0.25Zr0.50Ga5.25O14 single crystal (a = 8.2574(4) Å, c = 5.1465(4) Å, sp. gr. P321, Z = 1, R/R w = 0.62/0.57% for...