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.     

Dynamics and Cycle of Interstellar H2O and OH Masers

We present an improved radiative pumping model for interstellar H2O and OH masers.This oversomes the defects of former radiative models,and is compatible with astronomical conditions.For the regions of strong H2O and OH formation,it is shown that the rotational population is affected by collisions less than by radiation.A reasonable scheme for both regeneration and destruction of interstellar H2O and OH molecules is investigated.It can close the dynamical cycle of interstellar H2O and OH species,and can give an appropriate interpretation for both interstellar H2O and OH masers.This model has been confirmed by experiments.     

Thermal stability and photoluminescence property of hexagonal MoO3·0.55H2O microrods

The metastable phase of well-faceted, hexagonal, prism-like molybdenum oxide hydrate (MoO₃·0.55H₂O) was successfully synthesized by evaporating molybdic acid solution prepared through cation membrane electrolysis of Na₂MoO₄·2H₂O aqueous solution. The obtained crystals were characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electronic microscopy (SEM) and photoluminescence (PL) spectrophotometry. The as-prepared MoO₃·0.55H₂O rods were of 2–4 μm in width and 5–12 μm in length. The MoO₃·0.55H₂O microrods displayed photoluminescence properties at room temperature and were transformed into stable orthorhombic α-MoO₃ after air annealing at 380 °C. Moreover, the influence of temperature factor on the phase transformation process, morphology and photoluminescence properties of MoO₃·0.55H₂O was investigated in detail.     

A new acentric borate of K2Ba[B4O5(OH)4]2·10H2O: synthesis,structure and nonlinear optical property

A new acentric mixed metal borate of composition K₂Ba[B₄O₅(OH)₄]₂·10H₂O, has been successfully obtained by slow evaporation solution method. The compound crystallizes in the Orthorhombic space group Pna21 (No.33) with a = 16.8668(7) Å, b = 13.0903(5) Å, c = 11.5529(5) Å and Z = 4. [B₄O₅(OH)₄]^2? clusters serve as fundamental building unit linking with BaO₈, K1O₆, K2O₇ by common O atoms to form three-dimensional layer structure. The second harmonic generation measurements in the powder samples reveal that the compound exhibits approximately 0.5 times that of KH₂PO₄ (KDP) and phase matching.     

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.     

Vibrational studies of two phosphotellurates: Te(OH)62(NH4)2HPO4 and Te(OH)6Na2HPO4· H2O

IR and Raman spectra of the two phospsotellurates Te(OH)₆2(NH₄)₂HPO₄ and Te(OH)₆Na₂HPO₄· H₂O have been analysed on the basis of vibrations of HPO₄²⁻, TeO₆, NH₄⁺ and H₂O groups. It has been found that the NH₄⁺ ion rotates freely in the crystalline lattice. The splitting of the non-degenerate v_sPO₃, mode into two components suggests the possibility of resonance interaction between the HPO²⁻₄ ions in Te(OH)₆Na₂HPO₄· H₂O. The non-existence of H₃O⁺ ion in this crystal was also noticed.     

Characterisation of the Fermi surface and phase transitions of (BEDO-TTF)2 ReO4·(H2O) by physical property measurements and electronic band structure calculations

The electronic properties of the organic superconductor (BEDO-TTF)₂ ReO₄·(H₂O) were investigated by temperature dependent resistivity, ESR, Hall effect and magnetoresistance measurements. Shubnikov-de Haas (SdH) oscillations were observed in magnetic fields up to 24 T in the temperature range 0.5 K to 4.2 K. The electronic band structure of (BEDO-TTF)₂ ReO₄·(H₂O) was calculated by employing the extended Hückel tight binding method on the basis of its room temperature crystal structure. The two observed SdH frequencies of 75 T and 37 T correspond very well with two cross-sectional areas of the hole and electron Fermi surface pockets obtained from the tight binding calculation. From the temperature dependence of the SdH oscillation amplitudes, the cyclotron effective mass (m_c) belonging to the larger and smaller pockets were found to be 0.9 m₀ and m_c=1.15 m₀ respectively. Measurements of the angular dependence of the SdH frequencies show no deviation from that expected for a cylindrical Fermi surface. In terms of our tight binding calculations and experimental measurements, probable causes for the 213 K and 35 K phase transitions are discussed. The calculations show that (BEDO-TTF)₂ ReO₄·(H₂O) is a two dimensional semimetal but possesses a hidden nesting. The latter is likely to cause an SDW instability leading to the 35 K transition. The resistivity drop associated with the 213 K transition is likely to be induced by an abrupt increase in the relaxation time. The excellent agreement between the calculated and experimentally observed Fermi surface implies that, with decreasing temperature below 35 K, (BEDO-TTF)₂ ReO₄·(H₂O) gradually gets out of the SDW state and re-enters the original metallic state, in which it becomes superconducting below 2.4 K.Reported at the 13th Genral Conference of the Condensed Matter Division of the European Physical Society, Regensburg, March 1993     

Synthesis of single crystalline (NH4)2V6O16·1.5H2O nest-like structures

Novel nest-like (NH₄)₂V₆O₁₆·1.5H₂O structures made of nanobelts have been synthesized by a facile hydrothermal approach. The powder X-ray diffraction pattern of the sample reveals the monoclinic crystalline phase of (NH₄)₂V₆O₁₆·1.5H₂O. The scanning electron microscopy images of the sample obtained at 130 °C for 3 days exhibit nest-like morphology. The transmission electron microscopy result reveals that the nanobelts have a smooth surface. The selected area electron diffraction pattern of the nanobelts indicates single crystalline nature. The two major weight losses occur in thermogravimetric analysis which correspond to the removal of water and ammonia molecules. Further, calcination of the (NH₄)₂V₆O₁₆·1.5H₂O product results in the formation of orthorhombic phase of shcherbianite V₂O₅.     

Infrared absorption of O−H in thin films of hydrogenated Bi2Sr2CaCu2O8

Thin films of hydrogenated Bi₂Sr₂CaCu₂O₈ show three O–H vibrational absorption bands that shift upon deuteration with frequency ratiosv _O-H/v _O-D1.3, as expected for local modes. The band positions indicate that hydrogen atoms may be located at two different sites, namely in CuO₂ layers and, for the most part, in BiO double layers. The temperature dependences of these absorption bands give no hint of any direct interactions between the O–H vibrational modes and the superconducting phase transition.     

Correlation of dielectric properties,Raman spectra and calorimetric measurements of β-cyclodextrin-polyiodide complexes (β-cyclodextrin)2 ·BaI7 ·11H2O and (β-cyclodextrin)2 ·CdI7·15H2O

The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)₂·BaI₇·11H₂O and (β-CD)₂·CdI₇·15H₂O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba²⁺ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm^?1, 170?cm^?1 and 165–166?cm^?1 are due to the charge transfer interactions in the polyiodide chains.     

Eu(C8H7O3)3·C12H8N2·H2O配合物的合成与表征

合成了新的Eu(C8H7O3)3·C12H8N2·H2O配合物.并经元素分析、摩尔电导、IR、UV、1H NMR等表征,初步确定配体3-甲氧基苯甲酸以桥式双齿形式和Eu(Ⅲ)配位.     

Synthesis of monolayers and bilayers of cobalt oxyhydrates (Na,K) x (H2O) y CoO2− δ

Potassium sodium cobalt oxyhydrates (Na,K)_x(H₂O)_yCoO_{2? δ} were synthesized from γ-Na_0.7CoO₂ by using aqueous KMnO₄ solution in a one-pot process. Chemical and structural analyses revealed that a partial or even almost complete replacement of K⁺ for Na⁺ in the alkaline layers occurs. Direct formation of the c ≈ 13.9 Å phase is apparently associated with the larger size of K⁺ (～1.4 Å) as compared to Na⁺ (～1.0 Å). Formation of (Na,K) _x (H₂O) _y CoO_{2? δ} not only involves de-intercalation, oxidation and hydration processes, but also an ion exchange reaction. Based on a systematic study, the phase formation of (Na,K) _x (H₂O) _y CoO_{2? δ} with c ≈ 19.6 Å is a slow process, particularly when using aqueous KMnO₄ solution with low molar ratio of KMnO₄/Na. When comparing the Co K-edge X-ray absorption spectra of (Na,K) _x (H₂O) _y CoO_{2? δ} with those of Na _x (H₂O) _y CoO₂ obtained from Br₂/CH₃CN solution, the edge energy of the main peak of the bilayered hydrate is found to be 3.5 eV higher than that of the monolayered hydrate for (Na,K) _x (H₂O) _y CoO_{2? δ}. In contrast, the edge energy of the main peak of the bilayered hydrate is 0.4 eV lower than that of the monolayered hydrate for Na _x (H₂O) _y CoO₂. In addition, the hydration behavior of monolayered of (Na,K) _x (H₂O) _y CoO_{2? δ} is different from that of Na _x (H₂O) _y CoO₂. These results seem to suggest that they are two different systems.     

Synthesis, Crystal Structure and Luminescent Property of Complex [Tb0.1Gd0.9(TPTZ)(H2O)6]Cl3·3H2O

The complex [Tb_0.1Gd_0.9(TPTZ)(H₂O)₆]Cl₃·3H₂O was prepared through the reaction of 2,4,6-tris-(2-pyridyl)-1,3,5-triazine (TPTZ) with TbCl₃:GdCl₃ (0.1:0.9) in absolute ethanol at room temperature. Single crystal X-ray diffraction revealed that the metal atom is nine-coordinated with three nitrogen atoms from one TPTZ ligand and six oxygen atoms from six water molecules. The complex emits intense green fluorescence under ultraviolet light. The luminescence peaks correspond to the characteristic emission ⁵D₄→⁷F_J (J = 3–6) transitions of the Tb³⁺ ion.     

Raman spectroscopic study of the uranyl titanate mineral holfertite Ca x U2−x Ti(O8−x OH4x )·3H2O and the lack of metamictization

Raman spectra of the uranyl titanate mineral holfertite Ca _x U_2?x Ti(O_8?x OH_4x )·3H₂O were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO₂)²⁺ stretching and bending vibrations, U–OH bending vibrations, and H₂O stretching and bending. The mineral holfertite is metamict, as is evidenced by the order/disorder of the mineral. Unexpectedly, the Raman spectrum of holfertite does not show any metamictization. The intensities of the UO stretching and bending modes show normal intensity and the bands are sharp.     

Synthesis and optical properties of Co3O4 porous nanoplates converted from α-Co(OH)2 nanoplates

A two-step strategy has been developed for the preparation of pure cubic phase Co₃O₄ porous nanoplates with visible light photoluminescence.

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Crystal structure of the inverse weberite ZnFeF5(H2O)2, magnetic and mössbauer study of the antiferromagnet ZnFeF5(H2O)2 and ferrimagnet Mn FeF5(H2O)2

The room temperature crystal structure of the inverse weberite ZnFeF₅ (H₂O)₂ is refined from powder X-ray diffraction. The cell is orthorhombic (S.G. Imma, a = 7.475(1) →A, b = 10.766(1) →A, c = 6.594(1) →A, z = 4). Below T_N = 9(2) K, ZnFeF₅(H₂O)₂ becomes a 1-D antiferromagnet. This behaviour was characterized by susceptibility and magnetization measurements and Mössbauer spectroscopy. On the contrary, isotypic MnFeF₅(H₂O)₂ is confrimed to be a ferrimagnet below T_c = 39.5(1)K. Its magnetic and Mössbauer characteristics are, above and below T_c,and agree with a 3-D magnetic character. Ferrimagnetism could be due to frustration effects as in previously described Fe₂F₅(H₂O)₂.     

Collisional-Broadened and Dicke-Narrowed Lineshapes of H(2)(16)O and H(2)(18)O Transitions at 1.39 µm

We present results of a study on the self-broadening and broadening by nitrogen and oxygen of H(2)(16)O and H(2)(18)O lines in the 1.39-μm wavelength region using a distributed feedback semiconductor diode laser. To estimate the broadening coefficients, the absorption lineshapes were analyzed using the ordinary Voigt profile which provided good fits for most of the investigated lines. The broadening coefficients were found to be larger for nitrogen used as a perturber than for oxygen. This agrees with the fact that the quadrupole moment of N(2) is larger than that of O(2). Nevertheless, for lines involving high-rotational quantum number J, relatively smaller broadening coefficients were found and deviations of the measured profiles from the standard Voigt profile were observed. These deviations were ascribed as caused by Dicke-narrowing effect. Corresponding to this effect, collisional-broadening and narrowing coefficients were determined using the Nelkin-Ghatak profile which is suitable for the "hard"-collision model. The optical diffusion coefficients of the water in both nitrogen and oxygen gases were determined from the measurements of the collisional-narrowing coefficients. Copyright 2001 Academic Press.     

Quenching of tribo- and photoluminescence in a Tb2(SO4)3 · 8H2O + NaNO2 crystalline mixture

It is found that the addition of NaNO₂ to Tb₂(SO₄)₃ · 8H₂O crystals quenches tribo- and photo-luminescence from the latter. In the case of triboluminescence, the glow of both Tb³⁺* ions (solid component of triboluminescence) and N ₂ ^* molecules (gas component) is quenched. The NO ₂ ^? ion is known to be an efficient quencher of Tb³⁺ ion luminescence by the mechanism of radiationless energy transfer in solutions. That quenching takes place when a crystalline quencher is in contact with a crystalline phosphor and also with a gaseous (molecular) phosphor seems to indicate that the excitation energy is transferred not only within individual crystals but also between contacting surfaces of the phosphor and quencher and at the gas-solid interface.     

Structural and spectroscopic investigation of the N-methylformamide–water (NMF···3H2O) complex

In this work, theoretical studies on the structure, molecular properties, hydrogen bonding, and vibrational spectra of the N-methylformamide–water (NMF···3H₂O) complex will be presented. The molecular geometry was optimised by using Hartree–Fock (HF), second Møller–Plesset (MP2), and density functional theory methods with different basis sets. The harmonic vibrational frequencies are computed by using the B3LYP method with 6-311++G(d,p) as a basis set and then scaled with a suitable scale factor to yield good coherence with the observed values. The temperature dependence of various thermodynamic functions (heat capacity, entropy, and enthalpy changes) was also studied. A detailed analysis of the nature of the hydrogen bonding, using natural bond orbital (NBO) and topological atoms in molecules theory, has been reported.