EXAFS and EPR studies of inclusion compounds of the trans-[Cu(en)2(H2O)2]2+ in cucurbit[8]uril

This work describes EXAFS and EPR studies of inclusion compounds of the trans-[Cu(en)₂(H₂O)₂]²⁺ complex in the macrocyclic cavitand CB[8] at different stages of heat treatment in the hydrogen atmosphere in a temperature range of 200–330°C. The structure and composition of the nearest environment of copper atoms are characterized, and the interatomic distances and coordination numbers are determined. It is shown that the structure of the copper complex inside the cavitand CB[8] remains unchanged at the first stage of complex preparation and upon heating up to 280°C in hydrogen atmosphere. The copper environment corresponds to four nitrogen atoms and two oxygen atoms. Further temperature treatment at 330°C causes decomposition of the complex inside the cavitand without the formation of copper clusters.     

An EPR study of the transformation of Ni(cyclam)@CB[8] and Ni(cyclen)@CB[8] inclusion compounds during annealing in a hydrogen atmosphere

The features of pseudosymmetry in crystalline compounds with highly symmetric sublattices are discussed. The symmetry of sublattices higher than the crystal symmetry is manifested in elementary excitation spectra in the form of degenerations and quasidegenerations. The topology of spectral branches is not related to the value of the parameter estimating the degree of pseudosymmetry on the basis of the electron density fraction, which is invariant with respect to operations corresponding to additional symmetry.     

State of water in CB[6] and CB[8] cavitands

The state of water in cucurbiturils CB[6] and CB[8], which were synthesized in hydrochloric acid solutions of glycoluril and formaldehyde, was studied. The amount of water coordinated in the macrocycle cavity and on its portals was shown to depend on the moisture content of the medium, being 2.4 molecules per 1 molecule of CB[6] and 3.2 per 1 molecule of CB[8], and in CB[8] coordinated water exists in two energy states. The state with the vaporization parameters Δ_vap H ^○ _381.5 = 29.2±0.4 kJ mol^?1 and Δ_vap S ^○ _381.5 = 50.7±1.0 J mol^?1 K^?1 coincides with the state of water in CB[6]. For another state, the vaporization parameters are Δ_vap H ^○ ₃₇₃ = 31.7±0.5 kJ mol^?1 and Δ_vap S ^○ ₃₇₃ = 63.2±1.2 J mol^?1 K^?1. The number of molecules bound to the oxygen atoms of the macrocycle portals is 1.7 and 2.6 for CB[6] and CB[8], respectively.     

Hydrogen reduction of the Cu(acac)2 complex sorbed by cucurbit[8]uril

The hydrogen reduction of bis(2,4-pentanedionato)copper(II) sorbed by the cavitand cucurbit[8]uril has been studied. After sorption of the complex at 180°C, the crystal structure of the resulting phase differs from the structure of the individual compounds. EPR shows that the reduction of the complex with hydrogen at 250°C for 15 min leads to the loss of one of the ligands and formation of the coordination bond between the Cu²⁺ ion and a nitrogen atom of cucurbit[8]uril and the oxygen atom of the water molecule or OH^? group located in the cavitand cavity. The molecular structure of the resulting supramolecular compound has been optimized by density functional theory quantum-chemical calculations with the exchange-correlation functional with the use of the PRIRODA program package. EPR, EXAFS, and XANES show that an increase in the reduction time or temperature (to 280°C) leads to the formation of copper clusters.     

Molar extinction coefficients of IR absorption bands of Cu(II) dipivaloylmethanate

IR absorption spectra of an intracomplex chelate compound of Cu(II) bis-dipivaloylmethanate in the spectral range 4000–300 cm⁻¹ are investigated. A comparison is made between the spectra of the complex in different aggregative states: as a solution in heptane and as condensed films. The molar extinction coefficients of absorption bands are calculated. The extinction coefficients found are used to evaluate the thickness of Cu(dpm)₂ films. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 34–37, January–February, 2000.     

The thermodynamic properties of talyl-and phenylsilanes

The enthalpies of fusion of C₆H₅SiH₃, C₆F₅Si(CH₃)₃, and (C₆H₅)₄Si were obtained in scanning calorimetry measurements. Pressure over the condensed talylsilane 4-CF₃C₆F₄SiCH₃, phenylsilane C₆H₅SiH₃, and pentafluorophenylsilane C₆F₅SiCH₃, (C₆F₅)₂Si(CH₃)₂, and (C₆F₅)₄Si phases was measured by the static method with the use of membrane null manometers. Equations approximating the dependences of saturated vapor pressures on temperature and the enthalpy and entropy of vaporization were obtained.     

Influence of Morphological Defects on Thermophysical Properties of γ-Gd<Subscript>2</Subscript>S<Subscript>3</Subscript>

The temperature dependences of the heat capacity (C _p ) and the thermal conductivity (κ) in the temperature range from 300 to 773 K of polycrystalline gadolinium sulfide samples (γ-GdS _y ) with the deviation of the composition from the integer stoichiometric were studied. It was found that the thermal conductivity of gadolinium sulfides decreases monotonically and reaches 0.74 W/(m K) at T = 773 K for the composition y = 1.479, which is much lower than for the known single-crystal samples. The influence of morphological defects (boundaries of crystallites and dislocations) on the intensity of scattering of phonons is studied. It has been established that ceramic samples of gadolinium sulphides have a large heat capacity and a lower thermal conductivity, in comparison with monocrystalline samples of the same composition.     

Study of the properties and structure of nanosize membranes for acousto-optic devices

Polyimide films on BK7 glass, which are used to produce matrices for infrared detectors, have been synthesized. When these systems are investigated by monochromatic zero ellipsometry, the least difference between parameters of the incident light polarization, which are determined from suppression angles of polarizer and analyzer and calculated within a certain model, is obtained via introducing air between mounting glass and the film. Validity of the solution was verified by holding the film in water vapor; then, solution of the inverse problem of ellipsometry indicated the appearance of liquid water between the film and mounting glass. Data of the electron microscopy study were used to suggest a water penetration mechanism and develop a physical model of the system polyimide film/mounting glass.