Adsorption-energetic and IR spectroscopic studies of NH4 natrolite

The ammonium form of natural zeolite, natrolite, obtained by vapor phase ion exchange is similar to calcium-containing zeolites of the natrolite group in its de- and rehydration characteristics and the heats of immersion in water. The adsorption capacity and the heat of immersion in water are maximum after evacuation of the zeolite at 200 °C. The irreversible sintering of NH₄ natrolite occurs above 200 °C (up to 45% at 500 °C), accompanied by the formation of hydroxyl groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 359–361, February, 1998.     

Phosphorescence of aromatic molecules in complexes with crystalline β-cyclodextrin at room temperature

The rate constants for the quenching by oxygen of triplet states of aromatic molecules (naphthalenes-d₈ and-h₈, phenanthrene) forming inclusion complexes with crystalline β-cyclodextrin in water at 290 K are equal to 900–1300 L mol⁻¹s⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1450–1453, August, 1997.     

Water clusters in supramolecular inclusion hydrates. Crystal structure of decaazatricyclo[28.2.2.213.16]tetratriacontane nanohydrate

Inclusion compounds of solvate water molecules in a crystal matrix are investigated by X-ray diffraction analysis of a macrocyclic polyamine decaazatricyclo[28.2.2.2^13.16]tetratriacontane nanohydrate (I). When included in a crystal, water molecules are bonded by water-water (O-H...O) and water—macrocycle (0-H...N and N-H...O) hydrogen bonds, forming a linear cluster. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 993–1001, September–October, 1999.     

NMR spectra and the structure of the guest sublattice in the monocationic forms of clinoptilolite and heulandite

The¹H NMR spectra of the hydrated monocationic forms of clinoptilolite M₆[Al₆Si₃₀O₇₂]·nH₂O (M=Li, Na, K, Cs, NH₄; n=12–22) and M ₃ ^′ [Al₆Si₃₀O₇₂]·nH₂O (M′=Mg, Ca, Sr, Ba; n=20–24) and heulandite M₈[Al₈Si₂₈O₇₂]·21H₂O (M=Na, K) are divided into three types differing in the symmetry of tensors of magnetic dipole-dipole interactions of protons in zeolite water molecules. On the basis of model calculations it is shown that water molecules in the Cs, K, and Ba forms of clinoptilolite and the K form of heulandite are ordered in structural positions. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Zeorex Ltd., Sofia. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 891–900, September–October, 1996. Translated by L. Smolina     

Coordination polyhedra of hydration shells of Na+ and K+ cations in aqueous solutions

Simulation of the hydration of Na⁺ and K⁺ cations in dilute solution was performed by the Monte Carlo method. A novel approach to structural analysis of hydration shells of ions was developed. Specific sets of coordination polyhedra formed by water molecules of the first coordination sphere were found. Structural and energy characteristics of hydration were calculated. The effect of Na⁺ and K⁺ cations on the structure of the network of H-bonds and mobility of water molecules in hydration shells was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 852–857, May, 1999.     

Structural peculiarities of particle solvation inN,N-dimethylformamide

Monte Carlo computer simulation of infinitely dilute solutions of Cs⁺ and I⁻ ions and Xe atoms inN,N-dimethylformamide (DMF) was performed. Peculiarities of intermolecular interactions and structural properties of the solutions were investigated. The solvation enthalpies of cations and anions are close, but the energies of the ion-solvent and solventsolvent interactions differ appreciably. The solute particles affect the energy and structural properties of DMF only in spatially localized domains. The second solvation shell of the solute particles was not structurally allocated. Two structurally and energetically differing states of DMF molecules (with normal and anomalous orientation of the dipole moments) exist in solution of Cs⁺ cations. The anomalous orientation of DMF molecules is due to the solvation steric effect, packing, and kinematic factors. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 584–596, April, 2000.     

Study of intermolecular interactions in aqueous solutions by millimeter spectroscopy

The absorption of millimeter electromagnetic radiation (v=1.4, 1.71, and 5 cm⁻¹) by aqueous solutions of glycine (pH 6.1–6.2) in the concentration range of 0.5–2.5 mol L⁻¹ was measured. It was found that the absorbing ability of the water present in the solutions, is higher than that of pure water. This phenomenon is explained by the presence of a center of negative hydration in the structure of the glycine zwitterion, which results in an increase in the rotational mobility of water molecules immobilized in the hydrate shell of the glycine zwitterion. For Part 5, see Ref. 1. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1305–1307, July, 1997.     

Geometry and energy calculations of the Hs-III polyhedral gas hydrate framework

Geometrical parameters of the HS-III hexagonal water framework in clathrate hydrates are calculated using Zimmerman-Pimentel's hydrogen-bond potential. Thermal expansion of an empty framework along the a and c axes is studied. Dependences of H-bond strain energies during the ice Ih—clathrate framework transition on hexagonal unit cell parameters are calculated. It is shown that water molecules occupying different crystallographic positions differ considerably in partial energies. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 3, pp. 488–493, May–June, 1995. Translated by L. Smolina     

Molecular dynamic study of electric potentials in water clusters containing the sodium or chlorine atom

Molecular dynamics with design is used to calculate the electric potentials of isolated water clusters containing Na⁺ or Cl⁻. The number of water molecules in the clusters is from 4 to 14. It is noted that electrostatic interaction plays a dominant role in the clusters; the dependence of the dielectric constant of the cluster on the size of the latter is determined. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 66–73, January–February, 1998.     

Multiple bond migration with participation of a protophilic agent

Ab initio study of the pathways of migration of the double bond in the 3-methylthioprop-1-ene (1) and 3-methoxyprop-1-ene (2) molecules with participation of hydroxide ion was carried out by the RHF/6-31+G^* and MP2/6-31+G//RHF/6-31+G^* methods. Conformational isomerism of the initial molecules and reaction products was considered. The distinctions are discussed in the spatial and electronic structure of intermediate carbanions stabilized (for1) due to the negative hyperconjugation. Stationary points corresponding to complexes between the molecules under study and the hydroxide ion and between the corresponding carbanion and water molecule were localized on the potential energy surfaces of the proton transfer reactions. For2, the single-stage mechanism of prototropic rearrangement involving the H atom of the hydroxide ions was found to be more energetically preferable than the two-stage mechanism, whereas both mechanisms are expected to be equiprobable for1. For Parts 1–3, see Refs. 1–3. Translated fromIzvestiya Akademii Nauk. Seriya Kimicheskaya, No. 3, pp. 407–413, March, 2000.     

Molecular dynamic study of thermodynamic properties of water clusters containing sodium or chlorine ions

The molecular dynamic method with design is used to calculate the thermodynamic properties of isolated water clusters containing Na⁺ or Cl^-. The number of water molecules in the clusters is from 2 to 14. The size dependence of the microscopic analogs of pressure, isothermal compressibility, and surface tension of the clusters is determined. The effect of positive and negative ions on heteromolecular nucleation in vapor is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1092–1102, November–December, 1997.     

Computer simulation of the incommensurate structure of channel clathrates of thiourea by the atom-atomic potential method

The distribution of guest molecules of hexachloroethane along the axes of clathrate framework channels is described. There are two types of domains (regions of regular arrangement of guest molecules), alternating inside the channels and separated by domain walls. The domain walls are very stable in form. Reasons for the soliton-like motion of the domains along the channel axes are revealed. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 5, pp. 857–867, September-October, 1997.     

Synthesis and structure of layered fluorine-containing crystal hydrates based on aquacomplexes of noble metals

Crystal hydrates were synthesized based on aquaions of noble metals [M(H₂O)₆]F₃·nH₂O, where n = 3–8 and M = Ir, Rh. The structure of the resulting crystal hydrates with three aqueous molecules is characterized by the space group P3, Z = 1 and has a layered form. The positively charged layers [M(H₂O)₆F ₂ ⁺ which alter with negatively charged layers of the composition ∼_-·3H₂O, are located perpendicular to the c axis. According to X-ray structural and nuclear magnetic resonance data, the water molecules and the F_- ions in the negatively charged layers are disordered. Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 259–264, March–April, 1999.     

Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Molecular dynamic study of stabilization of the Cl−−Cl− anion pair in steam

This paper studies the formation of a stable anion pair as a result of cluster interactions with water molecules (the number of molecules n=4, 6, 8, and 14). The hydration shells of the clusters obtained in a preliminary calculation are destructed to form closed chains of properly oriented water molecules in the space between the anions. The type of the resulting structure depends on the number of shared water molecules. The character of stabilization of the anion pair, determined by calculating different energy terms, also changes as n increases. The cyclic structures obtained in the region of the anion pair differ considerably from the structure of isolated Cl⁻ (H₂O)_n clusters and that of the aqueous solution of NaCl. The capture of water molecules by the anion pair is manifested in the nucleation of industrial steam. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 289–298, March–April, 1996. Translated by L. Smolina     

Conformational analysis and steric effects of substituents in derivatives of 3-oxo-, 3-imino-, and 3-methylenecyclohexene

The equilibrium conformations and the inversion barriers of the rings in 3-oxo-, 3-imino-, 3-methylenecyclohexenes and in their methyl,tert-butyl, and phenyl derivatives were calculated by molecular mechanics. The unsubstituted molecules adopt a sofa conformation. The nonbonded interactions between substituents at positions 2 and 4 and the exocyclic double bond lead to a change in the conformation of the ring to a half-chair. The effect is enhanced as the volume of the substituent increases in the series of the oxo, imino, and methylene derivatives. Substituents at other positions of the ring affect only slightly the equilibrium conformation. The results of calculations were confirmed by X-ray structural analysis of 2-(4-benzoyloxybenzyl)-6-isopropyl-3-methylcyclohex-2-enone. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1995–2000, November, 1997.     

Dehydration-induced changes in the vibrational states of dioptase Cu6Si6O18·6H2O

This paper reports on the results of temperature studies (20–880°C) of the IR absorption spectra of dioptase crystals in the range 50–4000 cm⁻¹. During the dehydration of dioptase the state of water changes as follows: (1) initial state, (2) intermediate state with damped external vibrations of H₂O, (3) isolated water molecules with new hydrogen bonds, (4) formation of hydroxyls. The bands of the external virations of H₂O (1) vanish in state (2) because of the formation of vacancies in the six-membered water rings. The frequencies of the translation vibrations of 6H₂O in initial dioptase are close to those in liquid water: 169–170 and 277–290 cm⁻¹. A factor-group analysis of the dioptase vibrations in the space group C _3i ² is performed. All IR active vibrations 23A_u+23E_u are described. The thirty five bands observed in the IR spectra are assigned. The dehydration-induced deformations of the silicate rings are determined from the shifts of the vibrational bands of Si₆O₁₈. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 68–74, January–February, 1996. Translated by I. Izvekova     

Processes of dissociative electron capture by 20-hydroxyecdysone molecules

The peculiarities of dissociative electron capture by 20-hydroxyecdysone molecules with the formation of fragment negative ions were studied. In the region of high electron energies (5–10 eV), processes of skeleton bond rupture are accompanied by the elimination of H₂O and H₂ molecules. In the region of thermal energies of electrons (≈0 eV), the mass spectrum is formed mainly by the [M−nH₂O]^.− (n=1–3) and [M−H₂−nH₂O]^.− (n=0−3) ions that are generated exclusively by the rearrangement. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–712, April, 2000.     

Computer simulation of the structure of the hydration shells of calcium and calcium-water-zeolite a

A potential function is suggested to describe the interaction of the calcium ion with the water molecule using the tetrahedral model of the water molecule. Monte Carlo simulations of small clusters Ca(H₂O)_n (n≤20) and analyses of the resulting F-structures showed that the coordination number of Ca is 8. The structure of water adsorbed in the α-cavity of zeolite CaA depends predominantly on interactions with Ca²⁺ ions. The water molecule forms one hydrogen bond with an oxygen atom of the framework; the molecules are not hydrogen-bonded with each other. In this respect the structure of water in the Ca form of zeolite A resembles that in the Na form but differs from that in the K form. Institute of Physical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 88–97, January–February, 1996 Translated by L. Smolina