Synthesis, crystal structure, and spectroscopic study of K0.92(2) Zn0.08(2) H1.92(2) (PO4) (Zn-KDP)

The structure of K0.92₍₂₎ Zn_0.08(2) H_1.92(2) (PO₄) was determined using single-crystal X-ray diffraction. The crystal structure of the Zn-KDP belonged to the tetragonal space group $ \mathrm{I}\overline{4}2\mathrm{d} $ , with cell parameters of a?=?b?=?7.4487(5)?Å and c?=?6.9703(5)?Å, 386.73(5) Å3, Z?=?4, and R?=?0.023. Zn²⁺ ions were used as substitutes for K⁺ ions with hydrogen vacancy. The Zn-KDP single crystals were submitted to further Raman, infrared, and ¹H NMR studies to investigate chemical group functionalisation, possible bonding between the organic and inorganic materials, and partial substitution of K⁺ by Zn²⁺. The latter partial substitution was confirmed by the deviation of IR frequencies for O–H stretching, the variation of IR and Raman frequencies for stretching and bending vibrations ν(PO₄) of H₂PO₄, and the appearance of additional Raman (147, 386 and 481 cm^?1) vibrational bands. Electrical conductivity measurements were performed on polycrystalline pellets of Zn-KDP and pure KDP at room temperatures (RT) of up to 473K. In both cases, a conductivity jump close to 453K was observed, and a stronger increase of conductivity was measured.     

Existence of solutions to various rock types odel model of two-phase flow in porous media

We study the flow of two immiscible and incompressible fluids through a porous media c,onsisting of different rock types: capillary pressure and relative permeablities curves are different in each type of porous media. This process can be formulated as a coupled system of partial differential equations which includes an elliptic pressurevelocity equation and a nonlinear degenerated parabolic saturation equation. Moreover the transmission conditions are nonlinear and the saturation is discontinuous at interfaces separating different media. A change of unknown leads to a new formulation of this problem. We derive a weak form for this new problem, which is a combination of a mixed formulation for the elliptic pressure-velocity equation and a standard variational formulation for the new parabolic equation. Under some realistic assumptions, we prove the existence of weak solutions to the implicit system given by time discretization.     

K2M(H2P2O7)2·2H2O (M = Ni,Cu, Zn): ortho­rhom­bic forms and Raman spectra

The crystal structures of three isotypic ortho­rhom­bic dihydrogendiphosphates, namely dipotassium copper(II)/nickel(II)/zinc(II) bis­(dihydrogendiphosphate) dihydrate, K₂M(H₂P₂O₇)₂·2H₂O (M = Cu, Ni and Zn), have been refined from single‐crystal data. The M²⁺ and K⁺ cations are located at sites of m symmetry, and the P atoms occupy general positions. These compounds also exist in triclinic forms with very similar structural features. The structures of both forms are compared, as well as the geometry of the MO₆ octa­hedron, which is considerably elongated towards the water mol­ecules for M = Ni and Cu. Such elongation has not been observed among the other representatives of the family. A Raman study of the whole series K₂M(H₂P₂O₇)₂·2H₂O (M = Mn, Co, Ni, Cu, Zn and Mg) is reported.     

The Ever‐Surprising Chemistry of Boron: Enhanced Acidity of Phosphine⋅Boranes

The acidity‐enhancing effect of BH₃ in gas‐phase phosphine ? boranes compared to the corresponding free phosphines is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. Thus, the enhancement of the acidity of protic acids by Lewis acids usually observed in solution is also observed in the gas phase. For example, the gas‐phase acidities (GA) of MePH₂ and MePH₂ ? BH₃ differ by about 118 kJ mol^?1 (see picture).

     

Synthesis of a new flocculant based on poly(acrylamide-co-(N-octyl-4-vinylpyridinium bromide)) [AM5/VP5C8Br]-application for the turbidity removal from clay suspension

The interactions between poly(acrylamide-co-(N-octyl-4-vinylpyridinium bromide)) [AM5/VP5C8Br] cationic polyelectrolyte, and clay particles in dilute aqueous suspensions are studied in the aim of adsorption and flocculation. The extents of both phenomena are significantly influenced by the ionic strength of the medium. The adsorption of the clay particles on the copolymer chains occurs initially by the hydrophobic interaction. As flocculation mechanisms, the hydrophobic interaction between copolymer chains and the clay particles appears to be principal. In this work, we have prepared a copolymer which has been characterized by conductivity, viscosity, ¹H NMR, and FT-IR spectroscopies. The copolymer dosage and pH are two of the most important experimental parameters in the coagulation/flocculation operations used for study and optimization of the wastewater treatment operations. Under optimized conditions, 97% efficiency of the turbidity elimination, with a very low flocculant concentration of 3?ppm have been achieved in order to produce drinking water with standard limits around the world (< 1 NTU). The conclusion drawn on the basis of these results is that wastewater treatment using this new copolymer [AM5/VP5C8Br] has proved to be a good flocculant in overseeing of wastewater turbidity problems.     

3-Methyl-3a,4-Dihydro-3H-Thiochromeno[4,3-c]isoxazol

Abstract  The crystal structure of the title compound, C₁₁H₁₁NOS, was determined by an X-ray diffraction analysis. The compound crystallizes in the monoclinic space group P2₁/c with cell parameters a = 10.533(2) ?, b = 12.7826(19) ?, c = 7.6491(17) ?, β = 107.997(17)^°, V = 979.5(3) ?³ and Z = 4. The S containing heterocycle adopts a sofa conformation, whereas the 5-membered ring adopts an envelope conformation. The crystal packing is characterized by weak C–H···N contacts and π-stacking interactions. Graphical Abstract  The title compound, 3-methyl-3a,4-dihydro-3H-thiochromeno[4,3-c]isoxazol was synthesized by an 1,3 dipolar cycloaddition reaction and its crystal structure determined. Single crystal X-ray diffraction analysis reveals that the aromatic 6-membered ring is planar, whereas the ring containing the S atom adopts a sofa conformation and the 5-membered ring an envelope conformation. The methyl group is in an equatorial position.      

Nonparametric Estimation for Semi-Markov Processes Based on its Hazard Rate Functions

The problem of estimating the Markov renewal matrix and the semi-Markov transition matrix based on a history of a finite semi-Markov process censored at time T (fixed) is addressed for the first time. Their asymptotic properties are studied. We begin by the definition of the transition rate of this process and propose a maximum likelihood estimator for the hazard rate functions and then we show that this estimator is uniformly strongly consistent and converges weakly to a normal random variable. We construct a new estimator for an absolute continous semi-Markov kernel and give detailed derivation of uniform strong consistency and weak convergence of this estimator as the censored time tends to infinity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Na1.72Mn3.28(AsO4)3

The single crystal of sodium manganese arsenate (1.72/3.28/12), Na_1.72Mn_3.28(AsO₄)₃, used for analysis was prepared by solid‐state reaction at 1073 K. The compound crystallizes in the monoclinic system in space group C2/c. The structure consists of a complex network of edge‐sharing MnO₆ octahedral chains, linked together by AsO₄ tetrahedra, forming two distinct channels, one containing Na⁺ cations and the other occupied statistically by Mn⁺ and Na⁺ cations.     

Dual fluorescence of 4-N,N-dimethylaminopyridine. Role of hydrogen-bonded complex in the ground state

A correlation is shown between the appearance of the dual fluorescence of 4-N,N-dimethylaminopyridine (DMAP) solutions and the formation of hydrogen-bonded of complexes in the ground state. A comparative absorption study between pyridine, N,N-dimethylaniline and DMAP shows that the hydrogen-bonded complex is situated on the amino nitrogen of DMAP. A “pretwisted” conformation of DMAP in the ground state isassumed due to this hydrogen-bonded complex. Simulations by intermolecular interaction calculations and spectroscopic calculations (CNDO/s) confrim the “twisting” influence of water molecules (and/or any other hydrogen bonding) on the amine in the ground state. This “pretwisting” in the ground state by hydrogen bonding is common in many other aromatic amines. Moreover, the deforming role of hydrogen bonding in the ground state seems to be a general phenomenon in flexible aromatic molecules.