A computational study of N2···HHeF: comparison with N2···HArF and N2···HKrF

A weakly bound linear complex of N₂ and HHeF was found to be stable with respect to the constituent monomers by ab initio calculations at various levels of theory (MP2, MP3, MP4(SDQ) and QCISD) using a 6-311++G(2d,2p) basis set. The complex N₂···HHeF was found to have a zero-point vibrational energy corrected binding energy of 14.5?kJ mol^?1 (QCISD) and exhibits a large harmonic vibrational frequency blue shift of 375?cm^?1 for the He–H stretching vibration mode, with a diminished infrared intensity for this mode on formation of the complex. The frequency shift for this mode was also found to be very sensitive to the level of theory employed for the calculation, and is rationalized by considering intermolecular electrostatic and charge-transfer effects. The results for N₂···HHeF are compared with corresponding results for the related complexes N₂···HArF and N₂···HKrF, both of which contain the same proton acceptor molecule.     

Dielectric relaxation of α-cyclodextrin-polyiodide complexes (α-cyclodextrin)2 · BaI2 · I2 · 8H2O and (α-cyclodextrin)2 · KI3 · I2 · 8H2O

The frequency and temperature dependence of the real (ε′) and imaginary (ε″) parts of the dielectric constant of the polycrystalline complexes (α-CD)₂ · Bal₂ · I₂ · 8H₂O and (α-CD)₂ · KI₃ · I₂ · 8H₂O (α-CD = α-cyclodetrin) have been investigated over the frequency and temperature ranges 0–100 kHz and 120–300 K, respectively. The temperature dependences of ε′, ε″ and the phase shift φ show two steps, two peaks and two minima, respectively, revealing the existence of two kinds of water molecule, the tightly bound and the easily movable water molecules, in both complexes. The first peak of (T) or the first minimum of φ(T) presents the transformation of flip-flop hydrogen bonds to the normal state. The second ε″ (T) peak or φ(T) minimum corresponds to the easily movable water molecules or to a partial transformation of tightly bound to easily movable water molecules. For T > 270K both samples show semiconductive behaviour with energy gaps of 1.84eV for the (α-CD)₂ · BaI₂ · I₂ · 8H₂O complex and 1.36eV for the (α-CD)₂ · KI₃ · I₂ · 8H₂O complex. The conductivity at room temperature decreases in the order: (α-CD)₂ · BaI₂ · I₂ · 8H₂O > (α-CD)₂ · LiI₃ · I₂ · 8H₂O > (α-CD)₂ · KI₃ · I₂ · 8H₂O > (α-CD)₂ · Cd_0.5 · I₅ · 26H₂O. The relaxation time varies in a Λ-like curve (from 120 to 250 K) and rises rapidly for temperatures greater than 250 K, indicating the process of ionic movements. The activation energies around the transition temperature 0.98–1.09 k _B T _trans for (α-CD)₂ · BaI₂ · I₂ · 8H₂O and 1.06-1.55 k _B T _trans for (α-CD)₂ · KI₃ · I₂ · 8H₂O reveal the greater stability of the α-K complex against that of the α-Ba complex.     

Dielectric relaxation of α-cyclodextrin—polyiodide complexes (α-cyclodextrin)2 · LiI3 · I2 · 8H2O and (α-cyclodextrin)2 · Cd0.5 · I5 · 26H2O

The frequency and temperature dependence of real (?′) and imaginary (?″) parts of the dielectric constant of polycrystalline complexes (α-CD)₂ · LiI₃ · I₂ · 8H₂O and (α-CD)₂ · Cd_0.5 · I₅ · 26H₂O (α-CD = α-cyclodextrin) has been investigated over the frequency and temperature ranges of 0–100 kHz and 12–300 K. The dielectric behaviour is described well by Debye type relaxation (α-dispersion). Both systems exhibit an additional Ω dispersion at low frequencies which is attributed to ionic conductance and is much greater in the case of Li due to the greater mobility of cations Li⁺. The temperature dependence of ?′ reveals the existence of two kinds of water molecule in the case of the (α-CD)₂ · Cd_0.5 · I₅ · 26H₂O complex; these can be classified as tiqhtly bound and easily movable water molecules that cause two steps in ?′ versus T plots. In the case of the (α-CD)₂ · LiI₃ · I₂ · 8H₂O complex the water molecules are tightly bound and as a result only one step is observed in these graphs. These finding are also confirmed from the ?″_max versus T plots, which exhibit the same number of steps with ?′, and from calorimetric measurements. The order-disorder transition or the transformation of normal hydrogen bonds to flip-flop type has been observed as a peak in ?″ versus T plots that is more intense and narrow in the case of Li and less high but more broad in Cd. The relaxation time vanes in a α-like curve (from 120 K to 240 K) and rises rapidly for temperatures greater than 240 K, indicating the existence of a new process involving the breaking of hydrogen bonds (normal or flip-flop type). The calculated values of activation energy (0.35–0.62 k_BT_trans) reveal the greater stability of the Li compared with the Cd complex. The starting value of 8.2–8.4 μs for τ is the same as observed in β-CD complexes with guest 4-t-butylbenzyl alcohol (TERB). However, the activation energies of these are greater (1.1–1.7k_BT_trans), indicating greater stability for β-CD complexes.     

Protonic conduction and diffusion in the hydrous oxides V2O5·nH2O,Nb2O5·nH2O,Ta2O5·nH2O and CeO2·nH2O

Conductivity (ac and dc) measurements are reported for hydrous V₂O₅, Nb₂O₅, Ta₂O₅ and CeO₅ in the range 250<T/K<320. Ambient temperature conductivities increase with water content and (SEM) agglomerate size, the most highly conductive material being Ta₂O₅·3.92 H₂O (α₂₉₈=3×10⁻⁴S cm⁻¹). There is no simple composition dependence of conductivity activation energy. ¹H NMR relaxation time measurements in the range 170<t/K<330 are also reported. The data consistent with chemical exchange between a range of interparticle protonic environments, but there is no simple link with conductivities.     

3BaO·3B_2O_3·2GeO_2非晶体晶化过程的研究

3BaO·3B_2O_3·2Ge0_2是BaO-B_2O_3-GeO_2三元系中的一个三元化合物。本文用差热分析法对3BaO·3B_2O_3·2GeO_2非晶态晶化过程进行了研究,非晶的晶化温度随颗粒度减小而下降。用等温晶化法和峰值位移法测定了不同颗粒度的晶化激活能,非晶颗粒度越小,晶化激活能越大。     

关于Li_2O·P_2O_5·CdO玻璃的核磁共振研究

以~(31)P核为探针对具有不同摩尔比(x,y)的xLi_2O·P_2O_5·yCdO玻璃样品进行了核磁共振研究。通过Bruker MSL-300谱仪得到了静态核磁共振谱,工作频率为121.487MHz。 在玻璃中,三种基本类型的磷结构组元随机地连在一起形成网络,每种组无有自己的核磁共振特征,基本结构组元的相对含量依赖于Li_2和CdO的摩尔比,即依赖于x和y。 为了描述组元的含量,我们提出了一个简洁的模型,它的合理性已被其预言结果与对实验观测核磁共振粉末谱的拟谱结论的一致性所证实。     

Cooperative interaction between π-hole and single-electron σ-hole interactions in O2S···NCX···CH3 and O2Se···NCX···CH3 complexes (X = F,Cl, Br and I)

Ab initio calculations are performed to analyse the cooperative effects between π-hole and single-electron σ-hole interactions in O₂S···NCX···CH₃ and O₂Se···NCX···CH₃ complexes, where X = F, Cl, Br and I. These effects are investigated in terms of geometric and energetic features of the complexes, which are computed by UMP2/aug-cc-pVTZ(-PP) method. Our results indicate that the shortening of the each π-hole bond distance in the complexes is dependent on the strength of the σ-hole interaction. The maximum and minimum energetic cooperativity values correspond to the most and least stable complexes studied in the present work. The cooperativity between both types of interaction is chiefly caused by the electrostatic effects. The topological analysis, based on the quantum theory of atoms in molecules, is used to characterise the interactions and analyse their enhancement with varying electron density at bond critical points.     

K2O·CaO·4B2O3·12H2O∶Nd3+的合成及发光性能

以CaCl2、K2B4O7和Nd2O3为原料,采用易于工业化、无污染的水溶液法反应合成碱-碱土金属硼酸盐K2O·CaO·4B2O3·12H2O∶Nd3+晶体,利用X射线衍射、红外光谱、扫描电镜、荧光分光度计等现代分析测试手段,对所合成晶体进行了分析和表征.结果表明,所制备的K2O·CaO·4B2O3·12H2O∶Nd3...     

Magnetic transitions in K2MnCl4·2H2O

Results of (dM/dH) measurements on tetrahedral K₂MnCl₄·2H₂O as a function of temperature and magnetic field, are presented. An antiferromagnetic transition along the tetragonal axis is observed at T_N = (3.05±0.05) K. The H-T magnetic phase diagram was completely determined, and shows the usual characteristics of that of a low anisotropy antiferromagnet. The T = 0 critical fields are compatible with the values H_E = (29.2±0.3) kOe and H_A = (5.9±0.6) kOe for the exchange and anisotropy fields.     

K2O·CaO·4B2O3·12H2O∶Nd3+的合成及发光性能

以CaCl2、K2B4O7和Nd2O3为原料,采用易于工业化、无污染的水溶液法反应合成碱-碱土金属硼酸盐K2O·CaO·4B2O3·12H2O∶Nd3+晶体,利用X射线衍射、红外光谱、扫描电镜、荧光分光度计等现代分析测试手段,对所合成晶体进行了分析和表征.结果表明,所制备的K2O·CaO·4B2O3·12H2O∶Nd3+晶型发育良好、形貌规整.基质本身具有上转换发光特性,K2O·CaO·4B2O3·12H2O∶Nd3+的发光强度较基质弱.当激发源为828 nm时,材料呈橙红色光.     

Luminescence and absorption of Tb3+in mo·Al2O3·B2O3·Tb2O3 glasses

Quantum yields of the green Tb luminescence for 254 nm excitation of glass compositions in the system MO·Al₂O₃· B₂O₃·Tb₂O₃ (M = Mg, Ca, Sr, Ba and Zn) were studied in relation to absorption and excitation spectra. Yields as high as 80% were observed. The Tb 4f-5d absorption maximum ranges from 218 to 232 nm, always at a longer wavelength than the glass matrix absorption. The yield strongly depends on the spectral position of the 4f-5d absorption, due to competing impurity absorption at 254 nm.     

Surface segregation during the uptake of NO3 on coatings composed of NaI · 2H2O/NaBr · 2H2O and MgBr2 · 6H2O/MgCl2 · 6H2O binary salts: Solubility or deliquescence?

The uptake of NO₃ radicals on the surface of coatings prepared from the individual salts of NaI and NaBr dehydrates, hexahydrates of MgBr₂, and MgCl₂ and NaI · 2H₂O/NaBr · 2H₂O and MgBr₂ · 6H₂O/MgCl₂ · 6H₂O binary salts at various mole fractions of the doping salts, NaI · 2H₂O and MgBr₂ · 6H₂O in the initial aqueous solution was measured in a flow reactor by kinetic mass spectrometry. The dependences of the rates of the consumption of the reactant and of the formation of the products on the mole fraction of the doping salt made it possible to determine a quantitative relationship between the surface density of the doping salt and its mole fraction in the initial solution. A joint analysis of these dependences and the previously obtained data led to the conclusion that the deliquescence of the studied individual salts produces the predominant effect on the ratio between their surface densities.     

Effect of Li2O on the structure,electrical and dielectric properties of xLi2O·(20−x)CaO·30P2O5·30V2O5·20Fe2O3 glasses

Glasses of the general formula xLi₂O·(20?x)CaO·30P₂O₅·30V₂O₅·20Fe₂O₃ with x=0, 5, 10, 15 and 20 mol% were prepared; IR, density, electrical and dielectric properties have been investigated. Lithia-containing glasses revealed more (P₂O₇)^4?, FeO₆, V–O^? and PO^? groups and mostly have lower densities than those of lithia-free ones. The electrical properties showed random behavior by replacing Li₂O for CaO, which has been assigned to the change of the glass structure. The results of activation energy and frequency-dependent conductivity indicate that the conduction proceeds via electronic and ionic mechanisms, the former being dominant. The mechanism responsible for the electronic conduction is mostly thermally activated hopping of electrons from Fe(II) ions to neighboring Fe(III) sites and/or from V⁴⁺ to V⁵⁺. The dielectric constant (ε′) showed values that depend on the structure of glass according to its content of Li₂O. The (ε′) values are ranging between 3 and 41 at room temperature for 1 kHz, yet at high temperatures, glass with 20 mol Li₂O exhibits values of 110 and 3600 when measurement was carried out in the range 0.1–1 kHz, and at 5 MHz, respectively.     

A computational study of the linear and nonlinear complexes of FArCCH···N2

Linear and nonlinear weakly bound complexes of the metastable argon-containing compound FArCCH and N₂ were predicted to be stable from ab initio computations at the MP2/6-311++G(2d,2p) level of theory. Both complexes were found to have similar interaction energies and they exhibit red shifts of the C–H stretch, blue shifts of the Ar–C stretch and red shifts of the F–Ar stretch, in the same order as the stabilities. These effects are rationalized by considering changes in orbital occupancies on complexation, which are brought about by a combination of the intermolecular electrostatic interaction and charge density transferred from the N₂ molecule to the argon-containing molecule.     

Geometry,strength of binding and Br2 charge redistribution in the complex OC ··· Br2 determined by rotational spectroscopy

The ground-state rotational spectra of the six isotopomers ¹⁶O¹²C ··· ⁷⁹Br⁷⁹Br, ¹⁶O¹²C ··· ⁸¹Br⁷⁹Br, ¹⁶O¹²C ··· ⁸¹Br⁸¹Br, ¹⁶O¹²C ··· ⁷⁹Br⁸¹Br, ¹⁶O¹³C ··· ⁷⁹Br⁷⁹Br, ¹⁶O¹³C ··· ⁸¹Br⁷⁹Br, were observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B _O, D _J, χ _aa (Br_i), χ _aa (Br_o), M_bb (Br_i) and M _bb (Br_o), where i = inner and o = outer, were determined for each isotopomer. The complex is linear, with the weak bond between the C atom of CO and Br_i. The rotational constants were used to determine the distance r(C ··· Br_i) = 3.1058Å and to show that the Br—Br bond lengthens by ～0.005–0.01Å on complex formation. The intermolecular stretching force constant kσ = 5.0 Nm^?1 was obtained from D_J and the Br nuclear quadrupole coupling constants were interpreted to reveal that a fraction δ = 0.02 of an electronic charge is transferred from Br_i to Br_o when Br₂ is subsumed into the complex. Properties of the two series OC ··· XY and H₃N ··· XY, where XY = C1₂, Br₂ and BrC1, are compared.     

Das Schwingungsspektrum des monoklinen CaSO4·2H2O

The relations between the imaginary part of the optical dielectric tensor in molecular crystals and transitions active in absorption, derived in a preceding paper [1], are experimentally verified by investigating the vibrational spectrum of monoclinic crystals of gypsum. Reflection spectra of precisely oriented crystal sections were recorded using polarized light between 10 000 cm^?1 and 300 cm^?1 at room temperature and at about 15°K. The eigenfrequencies of polar vibrations and the direction and magnitude of transition moments in the crystal are derived from these spectra. These results definitely support the assumption, that the bands observed between 500 cm^?1 and 300 cm^?1 are caused by hindered rotations of the water molecules. The temperature dependence of the spectra of these molecules in the region of the two stretching modes indicates mixing of these states as a result of the crystalline field. Besides this, mechanisms are discussed, which lead to the decay of excited vibrational modes and thus give rise to the observed temperature dependence of the bandwidths.     

Anomalous elastic properties of betaine calcium chloride dihydrate, (CH3)3NCH2COO·CaCl2·2H2O

The elastic constants of orthorhombic betaine calcium chloride dihydrate have been investigated by ultrasonic methods in the range between 300 and 100 K. The phase transition at 169 K is accompanied by a sharp softening of all ultrasonic waves having longitudinal components of the displacement vector, similar to the effects observed at the - transition of Li₂Ge₇O₁₅ and at the V–IV transition of thiourea. The transition at 129 K shows only very weak anomalies like those found in the - transition of Te(OH)₆·2NH₄H₂PO₄·(NH₄)₂HPO₄. The transitions at 169 K and 129 K are of second order.     

Resonanzaufspaltung im Schwingungsspektrum des CaSO4·2H2O

The resonance- or Davydov- or correlationfield-splittings of the vibrational levels of CaSO₄·2H₂O (gypsum) are calculated using the exciton theory ofDavydov. This theory is extended to include the induced polarization of crystalline matter by the electric fields of the transition dipoles. The numerical calculations are based on an experimental determination of the transition dipole moments and on a calculation of the dipole lattice sums by the Ewald method. The results obtained show, that in most cases the assumption of Coulomb interaction between transition dipoles alone does not completely explain the observed splittings. However, the shift of transition frequency with an increasing longitudinally polarized component of a polar crystal vibration can be predicted by this theory within the limits of accuracy of the experimental determination of transition moments.     

Zero-field NMRON in54Mn-MnCl2·4H2O

We have observed NMRON lines for⁵⁴Mn doped into MnCl₂.4H₂O corresponding to ordering by a strong hyperfine field B_N=60.95 (6) T modified by a weak quadrupole interaction of strength P=+0.52 (7) MHz. The reduction of S_Z for the manganese ion is larger than expected. Point-charge estimates of P yield values which are positive, but smaller than the experimental value.