Phonon softening in (C2H5)4NFeX4 (X=Cl,Br)

Temperature-dependent¹⁶⁹Tm Mössbauer measurements are reported for the ternary intermetallic compounds TmT₂Ge₂ (T=Fe, Cu). Based on comparison with results for their TmT₂Si₂ counterparts, it is verified that the T constituent has the more significant influence on the crystal field interaction at the rare-earth site.     

Structural and magnetic phase transitions in (Chloroanilinium)2CuX4 (X = Cl, Br)

Successive structural phase transitions of (4-ClC₆H₄NH₃)₂CuCl₄, which occur in a very narrow temperature range were reinvestigated by Fourier transform nuclear quadrupole resonance (FT NQR) measurements. The phase transitions at 275.5 and 277.0 K were confirmed. The effect of the deuteration of the ammonium end on these transitions was studied. The³⁵Cl NQR frequencies of organic cation were observed to decrease by about 4 kHz and the phase transition temperatures to decrease by about 2 K by the deuteration, suggesting that the ?NH₃ ⁺ … Cl hydrogen bond is weakened by the deuteration. The magnetic phase transition temperature of 8.6 K showed no remarkable change within experimental error by the deuteration. It was found that the magnetically ordered state is broken by the radio-frequency magnetic field of about 15–35 Oe usually employed in pulsed NQR. However, in the deuterated compound (4-ClC₆H₄ND₃)₂CuCl₄, the ordered state was found to be stabler for the usual radiofrequency power. By combining with the NQR data of (4-ClC₆H₄NH₃)₂CuBr₄ and (3,5-Cl₂C₆H₃NH₃)₂CuCl₄, the possibility is discussed of tuning the interlayer interaction between the organic cation layer and the inorganic complex anion layer by the halogen substitution in the organic cation as well as by the halogen replacement in the inorganic complex anion.     

Lattice and molecular dynamics in (C2H5)4NFeX4(X=Cl,Br)

We have measured the thermal dependence of thef factor and the line shift of the title compounds, in order to determine the (−2) and (+2) moments of the Fe frequency spectrum. The latter is approximated by a superposition of an acoustic-wave band and an intramolecular optical mode. Our results show that both frequency bands are well separated, owing to a relatively weak interaction between tetrahedral units. Optical frequencies thus determined are consistent with Raman data. Debye temperatures were obtained for the low-frequency vibrations of both crystals.     

High-pressure magnetic and structural properties of TiOX (X=Cl,Br)

We report high-pressure diffraction and magnetization measurements to demonstrate that the partial collapse of electronic gap at high-pressure insulator to metal transition reported in TiOCl (C. Kuntscher et al. Phys. Rev. B 74 184402 (2006).) corresponds to a Ti³⁺–Ti³⁺ dimerization at room temperature within the space group P2₁/m. The shortest Ti–Ti distance is comparable to that of the Ti metal, but a Peierls-like distortion prevents a metallic behaviour.     

HX+2(X=Cl,Br)离子的密度函数理论(DFT)研究

选取密度泛函方法,采取6-311++G(2df,2pd)基组对单态HCl+2和HBr+2离子进行了理论计算.考虑到HF+2离子中D∞h结构可独立存在的事实,文中首次对HCl+2和HBr+2离子的包含D∞h在内的四种可能几何构型进行了优化计算;求得了Cl2与Br2的质子亲和能及Cl-ClH+与Br-BrH+的键分离能,丰富和完善了对HCl+2的理论计算,并对HBr+2离子存在的可能性进行了计算研究,结果预言HBr+2单态中Cs结构为其平衡结构.最后给出了HCl+2和HBr+2的热化学数据、力常数等数值,并给出了基态HBr+2离子的离解通道,从而给出其完全离解时的离解能,为该离子的分析势能函数的推导准备了必需的理论数据.     

Cation mobility in the Cu6PS5X (X=Cl,Br, I) argyrodites

The electrical conductivity of Cu₆PS₅Cl shows purely Arrhenius behavior throughout the temperature range 170–450 K with no evidence of the 241 K thermodynamic phase transition previously reported. Cu₆PS₅Br exhibits two changes in activation energy. The first, at 251 K, apparently coincides with a previously determined thermodynamic transition. The second, at 321 K, is likely associated with a conduction transformation from ionic to electronic. The conductivity of Cu₆PS₅I is characterized by a cusp at a temperature of 194 K, far removed from a previously reported thermodynamic transition at 221 K. In addition, a broad and continuous change in activation energy appears to coincide with another previously reported phase transition at 270 K.     

Luminescence of MeFX : Eu2+ (Me = Sr,Ba; X = Cl,Br)

Compounds of the type MeFX : Eu²⁺ with Me = Sr, Ba and X = C1, Br are efficient phosphors. Emission consists of both a 5d-4f band as well as 4f-4f lines, their relative intensities being strongly dependent on host lattice and temperature.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

Polarized Raman scattering from oriented single crystals of A2BX4 halides (A = Cs,B = Zn,X = Cl,Br, I)

Raman spectra of isostructural tetrahalozincates viz. Cs₂ZnI₄, Cs₂ZnBr₄ and Cs₂ZnCl₄ single crystals have been measured in various scattering orientations using polarized laser excitation. The lattice dynamics of the crystals is probed down to 70 K in order to cover the successive phase sequences. Except Cs₂ZnI₄, none of the other salts shows the characteristic commensurate-incommensurate features of lattice instabilities. The unit cell dynamics is understood in terms of 84 phonon branches originating from various internal modes of tetrahedral ZnX²⁻₄ group and external lattice modes. The enormous splittings, responsible for a complete loss of degeneracy in the internal modes for all the three salts, suggest a considerable distortion particularly at low temperatures in the tetrahedral geometry of the ZnX²⁻₄ group.     

晶体NiX2(X=Cl,Br,I)的光谱和电子顺磁共振谱研究

在强场耦合图像中,采用双自旋-轨道耦合(SO)参量模型建立了过渡族3d2(3d8)离子的三角对称下全组态光谱能级和电子顺磁共振(EPR)公式.与经典的晶体场理论(仅考虑中心金属离子的自旋-轨道耦合作用)相比较,该公式还包括了配体离子的自旋-轨道耦合作用的贡献,这一模型在应用于计算共价性较强的晶体光谱和电子顺磁共振谱可得到合理的结果.作为验证,用完全对角化方法研究了品体NiX2(X=Cl,Br,I)的光谱和电子顺磁共振谱,结果表明,理论与实验很好地符合.建立的全组态谱能级和电子顺磁共振公式为更精确地计算光谱和电子顺磁共振谱提供了一条可行方法.     

Optical properties of the alkaline-earth fluorohalides matlockite-type structure SrFX (X=Cl, Br, I) compounds

The optical properties of the SrFX (X=Cl, Br, I) compound have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for band structure calculations. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε₁(0). We find that the value of ε₁(0) increases on decreasing the energy gap. The reflectivity spectra and absorption coefficient have been calculated and compared with the available experimental data.     

活性氮反应产生激发态卤化氮实验研究

报道了利用氮气放电产生的活性氮有效制备激发态卤氮自由基NX(b)(X=F,Cl,Br)的方法.在流动余辉装置上,将含溴有机物CH2Br2、CHBr3、C2H5Br、C4H9Br加入到活性氮中,在550～750nm观察到了较强的NBr(b→X)跃迁发射光谱.机理分析表明,活性氮中的基态氮原子N(4S)与含溴分子反应首先产生基态的NBr,由于亚稳态分子N2(A3Σ+u)的能量转移作用,基态NBr被激发到NBr(b).当含氯有机物CCl4、SOCl2加入到活性氮中时,观察到了NCl(b→X)的发射光谱,而当CHCl3、CH2Cl2加入到活性氮中时,却没有观察到NCl(b)态的辐射跃迁.当SF6与氮气混合放电时,观察到了NF(b)态的跃迁发射谱.分析表明,基态的NCl和NF自由基分别是由N(4S)+CCl3(SOCl2)→NCl(X)+CCl2(SOCl)和N(4S)+SF5→NF(X)+SF4通道产生的,再通过N2(A)能量转移到激发态.     

Study on the local structure and EPR spectroscopy of compressed CuX4 (X = N,S, Cl and Br) tetrahedral cluster

The spin Hamiltonian parameters g and A for copper(II) in CuX₄ (X = N, S, Cl and Br) tetrahedrons are theoretically investigated within a uniform model by utilizing the perturbation method and cluster approach for 3d⁹ ions suffering D_2d symmetry in view of host structures and angular distortions in terms of a single parameter β. For all the studied polymers, the isotropy of g tensors g_av and the hyperfine structure constant component A_‖ are found, respectively, to undergo an increasing and decreasing trend with the enlarging average X–Cu–X angle β, while the obtained cubic crystal field parameter D_q and isotropic Fermi contact constant κ are experiencing a declining and growing tendency with the rising Cu–X bond length, respectively. The critical angle β_c is concluded locating in the range of 109.471°–120° in which the g-isotropy value would reach the maximum, while the hyperfine structure factor might vanish that needs to be verified in future X-ray and EPR experiments. This work would be beneficial to the establishment of complete EPR and structure diagram for CuX₄ complexes and the synthesis of new compounds possessing novel physical and chemical properties.     

X-ray excited optical luminescence studies on the system BaXY (X,Y=F, Cl, Br, I)

The present paper reports the experimental observations on the x-ray excited optical luminescence (XEOL) along with the afterglow and colour center features found for the barium salts, represented by the formula,BaXY, whereX andY are the halides. The system thus consists of four dihalides (BaF₂,. . . ,BaI₂) and six mixed halides (BaFCl,. . . ,BaBrI). To start with, it was found that on two of the binary halides of barium, BaClI and BaBrI, no literature exists, and so these were prepared for the first time and their crystal structures were determined. An x-ray generator of 3-kW rating was next coupled to a spectrometer via a high throughput fiberoptic sensor for recording the luminescence spectra under x-irradiation. Also presented in this paper are the observations on the BaXY compounds in which about 0.1 mole% of Eu²⁺ was doped, in order to study the efficiency between the prompt luminescence and the photostimulated luminescence in these compounds. The crystal structure varies from fluorite (BaF₂), to matlockite (BaFX) and finally to orthorhombic (BaCl₂,. . .,BaBrI) for these compounds. Hence searching for systematics and empirical relations in the observed XEOL behaviour of these compounds is still a challenging problem.     

A comparative study and development of an improved method for the reduction of nitroarenes into arylamines by Al/NH4X (X=Cl, Br, I) in methanol under ultrasonic conditions

Nitroarenes were shown by us earlier to undergo reduction when treated with Al/NH4Cl in methanol under sonic conditions to give anilines in high yields [D. Nagaraja, M.A. Pasha, Tetrahedron Lett. 40 (1999) 7855]. Now, a comparative study has been carried out and an efficient and improved procedure for this reduction by using Al/NH4X (X=Cl, Br, I) is reported. A plausible mechanism of the reaction is envisaged.     

Halogen bond between hypervalent halogens YF3/YF5 (Y=Cl,Br, I) and H2X (X= O,S, Se)

ABSTRACT

The complexes of H₂X (X?=?O, S, Se) with hypervalent halogens YF₃ and YF₅ (Y?=?Cl, Br, I) have been studied. The σ-hole on the Y atom participates in a halogen bond with the lone pair on the chalcogen atom. In addition, some secondary interactions coexist with the halogen bond in most complexes. The interaction energy correlates with the nature of both X and Y atoms. In most cases, the complex is more stable for the heavier Y atom and the lighter X atom. Of course, there are some exceptions in H₂X···YF₃. YF₃ forms a more stable complex with H₂X than does YF₅. These complexes are dominated by electrostatic interaction and the halogen bond involving H₂S and H₂Se exhibits some covalent character.

Halogen bond plays an important role in chemical reactions and multivalent halogens can regulate chemical reactions by participating in a halogen bond. Thus we compare the effect of the chalcogen electron donor on the strength and nature of halogen bonding involving multivalent halogens.     

KX（X=Cl,Br,I）晶体中Eu^2＋离子的4f^65d态能级计算

按着4f~6(~7F_J)和5dΓ_1耦合模型,提出了计算KX(X=Cl,Br,I)晶体中Eu~(2+)离子4f~65d能级的方法,导出了能级的参数表达式,并进行了数值计算,计算结果和实验符合较好.     

Photostimulated luminescence in BaX 2 :Eu 2+ (X=Br,Cl) X-ray storage phosphors

The photostimulated luminescence (PSL) effect in BaX 2 :Eu 2+ (X=Br, Cl) is comparable to that observed in BaFBr:Eu 2+ which is used in commercial X-ray storage phosphor screens. After X-irradiation the PSL stimulation spectra of BaX 2 :Eu 2+ (X=Br, Cl) single crystals are identical to the F centre absorption spectra, i.e. the F centres are the PSL-active electron trap centres. The nature of the hole centres is still unknown. The PSL response time of about 0.70 v s is within experimental error of 0.02 v s identical to the Eu 2+ radiative lifetime, whereas in BaCl 2 :Eu 2+ the PSL response time is 0.60 v s, and thus longer than the Eu 2+ radiative lifetime of 0.47 v s.     

Progress in science and technology on photostimulable BaFX:Eu (X=Cl, Br, I) and imaging plates

Imaging plate (IP) is a two-dimensional detector of ionizing radiation utilizing photostimulable BaFX:Eu²⁺ (X=Cl, Br, I). First type was developed about 20 years ago. As for the mechanism of the photostimulated luminescence (PSL), a lot of arguments have been done after the presentation of the first model by Takahashi et al. In principle, the model is supported by the recent papers.

In the meantime, the performance of IPs is drastically improved. Then, the computed radiography and the radioluminography (RLG) systems, which take advantage of the excellent feature in linearity and high sensitivity of IPs, were developed that became an inevitable equipment for medical diagnostics and scientific research. The late Professor Shigeo Shionoya greatly contributed to analysis of the PSL mechanism and development of the RLG technology.