The crystal structure of tetrammine copper sulphate Cu(NH3)4SO4·H2O

The crystal structure of tetrammine copper sulphate was determined. The orthorhombic unit cell with dimensions a=12.12, b=10.66, c==7.07 Åcontains four molecules of Cu(NH ₃)₄ SO ₄.H ₂ O, the space group is Pbnm (D _2h ¹⁶ ).The atomic coordinates were determined from the projections of the Patterson function and the electron density onto the (001) and (010) planes. The complex cation Cu(NH ₃)₄ ⁺⁺ is approximately planar, the groups of NH ₃ are linked by co-valent bonds to the central Cu atom. The average distance of the groups of NH ₃,which are approximately at the corners of a square surrounding the central Cu atom, is 2.90 Å, the distance Cu-NH ₃,corresponding to the co-valent bond, is 2.05 Å.     

Effect of γ irradiation on the heat capacity of (CH3)2NH2Al(SO4)2 · 6H2O crystals near the ferroelectric phase transition

The heat capacity of dimethyl ammonium-aluminum sulfate crystals (DMAAS), both nonirradiated and γ-irradiated to fluences of 10⁷, 5×10⁷, and 10⁸ R, has been measured by the adiabatic method near the ferroelectric phase transition (PT) within the 80–300 K temperature range. The C _p =f(T) curve exhibits a λ-shaped anomaly near the phase-transition point T _C =152 K. The PT temperature and the magnitude of the anomaly are shown to decrease with increasing γ-irradiation fluence. It has been established that the ferroelectric PT at T _C =152 K, which lies close to the tricritical point, shifts progressively more under γ irradiation toward the second-order PT, and that the behavior of the anomalous part of the heat capacity in the ferroelectric phase is described by the thermodynamic theory of Landau. The experimental heat-capacity data have been used to calculate the variation of the thermodynamic functions of the DMAAS crystal.     

一种新型钼磷酸盐杂多化合物(NH3CH2CH2NH3)7H2[NaMo12O30(PO4)2(HPO4)5(H2PO4)]·7H2O的合成和光谱研究

本文采用水热反应条件 ,合成得到一种新型的含五价钼原子的杂多化合物 :(NH3CH2 CH2 NH3) 7H2[NaMo1 2 O30 (PO4 ) 2 (HPO4 ) 5(H2 PO4 ) ]·7H2 O ,在晶体结构测定的基础上对其进行红外、拉曼和紫外 可见漫反射光谱研究。结果表明 :较长的Mo(Ⅴ )—O键键长和分子内大量的氢键造成化合物红外光谱特征的红移。     

Ultrasonic Studies of (CH3)2NH2Al(SO4)2 · 6H2O crystals irradiated by γ quanta and electrons

The temperature dependence of the longitudinal-ultrasound velocities in (CH₃)₂NH₂Al(SO₄)₂ · 6H₂O crystals was studied using the echo-pulse technique in the 90–300 K range. The measurements were carried out along mutually perpendicular crystallographic directions X, Y, Z on samples both unirradiated and irradiated to various doses by γ quanta and an electron beam. The ultrasound velocity V in this crystal was shown to be anisotropic, with V _YY >V _XX >V _ZZ . The V _XX =f(T), V _YY =f(T), and V _ZZ =f(T) curves exhibit anomalies in the form of breaks at the ferroelectric phase transition (PT) at T _c1=152 K, as well as in the region of T _c2=218 K. It was established that as the irradiation dose increases, the PT temperature T _c1 decreases and the anomalies in the temperature dependences of the ultrasound velocities are smeared.     

Spin-lattice relaxation time of Yb3+ in YbCl3·6H2O

Temperature dependence of experimentally determined spin-lattice relaxation time τ_Yb of Yb³⁺ ions in YbCl₃·6H₂O single crystals is examined. It is found that τ_Yb has different temperature dependences in the temperature ranges 2–30 K, 30–77 K, 150–300 K. In particular, Raman mechanisms are found to be predominant in the temperature ranges 2–30 K and 150–300 K, while the direct process is predominant in the range 30–77 K.     

Investigation of the EPR parameters of the rhombic Cu2+ center in (NH4)2Mg(SO4)2·6H2O single crystal

The electron paramagnetic resonance (EPR) parameters (g factors g_x, g_y, g_z and hyperfine structure constants A_x, A_y, A_z) for Cu²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O (DHMS) crystal are theoretically investigated using the high-order perturbation formulas of these parameters. In the calculations, the ligand orbital and spin–orbit coupling for the impurity Cu²⁺ are taken into account; the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the local structure of the impurity center. The ligand orbital and the spin–orbit coupling contributions are included on the basis of the cluster approach. Based on the calculation, the theoretical EPR parameters show good agreement with the observed values. The results are discussed.     

Structural phase transition in a perovskite-type NH3(CH2)3NH3CuCl4 crystal – X-ray and optical studies

X-ray powder studies and optical studies (polarized microscopic observation and linear birefringence studies) of the crystal NH₃(CH₂)₃NH₃CuCl₄ are presented. The X-ray powder studies revealed a change of symmetry from orthorhombic room-temperature phase to monoclinic phase above 434 K. A reversible phase transition of the first order at 434 K on heating and 432 K on cooling was observed in birefringence studies. Optical polarized microscopic observation revealed monodomain and multidomain states in the room-temperature orthorhombic phase with domain walls in (110) and (1-10) planes. The hypothetical prototypic phase is expected to be tetragonal. The change of symmetry from orthorhombic to monoclinic and expected domain structure was found above 434 K in the (010) plane.     

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.     

Weak exchange interactions in the heteronuclear crystal CuPr2(CCl3COO)8·6H2O

The new heteronuclear crystal CuPr₂(CCl₃COO)₈·6H₂O, constructed of chains containing copper and praseodymium atoms, has been synthesized and investigated by EPR at 9.3 GHz at temperatures ranging from room temperature down to 10 K. At temperatures T∼300–130 K, EPR spectra are observed which are characteristic of isolated polyhedra of copper ions with g _z=2.330±0.005, g _x,y =2.053±0.005, A _z=139×10⁻⁴ cm⁻¹, and A _x,y <26×10⁻⁴ cm⁻¹. At temperatures T<130 K a complex spectrum is observed, associated with the appearance of weak exchange interactions between the copper ions in the chain (J _Cu-CuΣS _i·S _i+1), comparable in magnitude with the hyperfine interactions J _Cu-Cu=0.015 cm⁻¹ at T=10 K. The magnitude of the exchange interaction decreases smoothly as the temperature is raised. It is conjectured that orbitals of the praseodymium ions participate in the process of indirect exchange between the copper ions. Fiz. Tverd. Tela (St. Petersburg) 41, 2154–2157 (December 1999)     

Superionic phase transition in (NH4)2SeO4·2NH4HSeO4 single crystal at 378 K

Abstract

DTA, structural and electric conductivity investigations were made for (NH₄)₄H₂(SeO₄)₃ single crystals. A high-temperature phase transition at 378 K to a superionic phase was found. The phase is characterized by a high electrical conductivity (～4.10^?3 Ω^?1 cm^?1) and a low activation energy (0.11 eV).     

Low-temperature x-ray diffraction studies of the crystallographic parameters and thermal expansion of (CH3)2NH2Al(SO4)2 · 6H2O crystals

The a, b, c, and β crystallographic parameters of the (CH₃)₂NH₂Al(SO₄)₂ · 6H₂O crystal (DMAAS) have been measured by x-ray diffraction in the 90–300-K temperature range. The thermal expansion coefficients along the principal crystallographic axes α_a, α_b, and α_c have been determined. It was shown that, as the temperature is increased, the parameter α decreases and b increases, whereas c decreases for T<T _c (where T _c is the transition temperature) and increases for T>T _c, so that one observes a minimum in the c=f(T) curve in the region of the phase transition (PT) temperature T _c ～ 152 K. The thermal expansion coefficients α_a, α_b, and α_c vary in a complicated manner with increasing temperature, more specifically, α_a and α_c assume negative values at low temperatures, and the α_a=f(T), α_b=f(T), and α_c=f(T) curves exhibit anomalies at the PT point. The crystal has been found to be substantially anisotropic in thermal expansion.     

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.     

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.     

Electron paramagnetic resonance of Gd3+ in Nd2(SO4)3 · 8H2O single crystal

Electron paramagnetic resonance study has been carried out in Gd3+ doped single crystals of Nd₂(SO₄)₃·8H₂0 at three different temperatures. Two magnetic complexes exhibiting orthorhombic or lower symmetry are found and the results have been fitted to a suitable spin-Hamiltonian. The ten “best fit” parameters are obtained from two computer programs. Zero-field splittings of Gd3+ have been deduced from spin-Hamiltonian parameters and are compared with those observed directly by Bogle and Symmons. Fine forbidden transitions ∥ΔM_s∥ I > 1 are analyzed using numerical solution of the Hamiltonian matrix.     

NH3(H2O)4稳定结构的理论研究

先构建氨水团簇的模型势,并计算得到NH3(H2O)4的模型势异构体,从中选取稳定性较好的异构体作为初始结构,分别利用密度泛函方法和二级微扰理论在6-31G(d)和6-311++G(d,p)基组水平上逐级进行结构优化、频率和单点能计算.发现包括第2和第3稳定结构等12种新异构体;NH3(H2O)4的五边形环状结构的稳定性最好;这种极性混合分子簇的偶极矩大小和包含的氢键数都与结构的稳定性无必然联系.     

Electron paramagnetic resonance of quasi-one-dimensional crystal [Nd2(Cl3COO)6(H2O)3]n · nH2O

A quasi-one-dimensional single crystal of [Nd₂(Cl₃COO)₆(H₂O)₃]_n · nH₂O in which chains are built up of two alternating neodymium-ion dimer fragments is studied by the EPR technique. It is found that anisotropic interactions between neodymium ions in a chain are responsible for the complex shape of the EPR spectrum. Two groups of EPR signals are distinguished in the spectrum. Each group corresponds to one of the chain dimers disturbed by the interaction with neighbors in the chain. The shape of the EPR spectra is interpreted as a superposition of the spectra of chain fragments which have different lengths and are formed by the alternating magnetic triplet and nonmagnetic singlet states in the chain. Consideration is given to two cases when two alternating dimer fragments are either equivalent or nonequivalent to each other. It is shown that the spectral shape is primarily determined by the superposition of the spectra of an isolated triplet state (S=1), two interacting triplet states, and three interacting triplet states whose weighting contributions differ for the above two cases. The tensors of the anisotropic spin-spin interaction are determined, and the contribution from the isotropic component of the interaction is estimated.     

Isotopic effect in Brillouin light-scattering spectra of a Cs5H3(SO4)4 · xH2O crystal

A Brillouin scattering study of the behavior of hypersonic longitudinal acoustic phonons in crystalline pentacesium trihydrogen tetrasulfate Cs₅H₃(SO₄)₄ · xH₂O (PCHS) and its deuterated analog Cs₅D₃(SO₄)₄ · xD₂O (DPCHS) at temperatures ranging from 420 to 120 K is reported. The effect of deuteration on the crystal lattice dynamics is investigated. The differences in the behavior of hypersonic acoustic phonons in the PCHS and DPCHS crystals suggest the existence of a hydrogen isotope effect in both the high-and low-temperature phases. A possible model of the isotopic effect in the high-temperature phase is discussed. An analysis is made of the acoustic response of the PCHS and DPCHS crystals in the region of the transition to the glasslike phase.     

Interfacial and mechanical properties of carbon fibers modified by electrochemical oxidation in (NH4HCO3)/(NH4)2C2O4·H2O aqueous compound solution

Polyacrylonitrile-based carbon fibers were electrochemical oxidized in (NH₄HCO₃)/(NH₄)₂C₂O₄·H₂O aqueous compound solution to improve its tensile strength and interfacial bounding strength with resin matrix simultaneously. AFM, XPS, XRD and Raman spectra were employed to characterize morphology, chemical states, crystallites size and ordered degree of CFs surface. The results indicated that the optimal modified condition in this paper could increase the tensile strength of CFs by 17.1%, meantime improve the interlaminar shear strength (ILSS) by 14.5%. The improvement of interlaminar shear strength not only causes by increase of surface roughness, but also causes by interaction effects of oxygen-containing and nitrogen-containing functional groups on carbon fibers. Among oxygen-containing functional groups, –COOH functional group plays an important role in enhancing the ILSS. Furthermore, after electrochemical oxidation the crystallites size decreased by 23–27%; ordered degree on CFs surface has an increase with suitable etching which did not peel off the ordered region on CFs surface and create new cracks; both above increase the tensile strength of CFs.     

Topology of spin Hamiltonian and crystal field tensors for Mn2+ in ZnSeO4·6H2O crystal

The expansion of the {B ₂} and {B ₄} tensors of the spin Hamiltonian (SH) for Mn²⁺ (⁶S-state) is performed in terms of the irreducible tensor products {V _{L 1} ?V _{L 2}}₂ and {V _{L 1} ?V _{L 2}}₄ of the crystal field (CF) tensors {V _{L 1}} and {V _{L 2}}. The EPR spectra of Mn²⁺ in the ZnSeO₄·6H₂O crystal are studied and the SH tensors {B ₂} and {B ₄} are calculated. The tensors {V ₄?V ₄}₂ and {V ₄?V ₄}₄ are computed using the point-charge model (PCM) of the [Zn(H₂O)₆] complex with the C₂ symmetry and are compared with the SH tensors {B ₂} and {B ₄}, respectively. The correct signs of the elements and the pseudo-symmety axes of the tensors are obtained both for the {B ₂} tensor and {V ₄?V ₄}₂ and for the {B ₄} tensor and {V ₄?V ₄}₄. It is concluded that the irreducible tensor products {V ₄?V ₄}₂ and {V ₄?V ₄}₄ provide the predominant contribution respectively to the SH tensors {B ₂} and {B ₄} of Mn²⁺.