Chlorine Pentafluoride

The bonding in the halogen polyfluorides is similar to that in the xenon fluorides. Since XeF(4) exists, the previously unreported ClF(5) should exist. This compound has been prepared by heating ClF(3) in the presence of fluorine at high pressure. Chlorine pentafluoride is a square pyramidal molecule. It has a lower melting point than ClF(3) and a higher vapor pressure. It is also less reactive than ClF(3).     

Xenon hexafluoride: structural crystallography of tetrameric phases

Three crystalline phases of xenon hexafluoride are based on tetrameric association of XeF(5)(+) and F(-) ions into eight-membered rings. Phase I (monoclinic, 8 XeF(6) units per cell) transforms at approximately 10 degrees C to phase II (orthorhombic, 16 XeF(6) units per cell), which in turn transforms at approximately -25 degrees C to phase 111 (monoclinic, 64 XeF(6) units per doubly primitive cell). The transformation from phase I to phase II requires gross reorientation of half of the tetramers in the structure. The transformation from phase II to phase III involves only an ordering of right-handed and left-handed configurations.     

Xenon Oxyfluoride

The incomplete hydrolysis of XeF(6) has been used to prepare a xenon oxyfluoride, XeOF(4). The latter is a clear, colorless liquid, freezing at -41 degrees C. The infrared and Raman spectra show that the XeOF(4) molecule has a fourfold symmetry axis. The large Xe-O stretching force constant indicates the Xe-O bond has appreciable double bond character.     

Xenon Fluorides: Fluorine-19 Nuclear Magnetic Resonance Spectra

Chemical shifts have been measured for liquid XeF(2), XeF(4), XeOF(4), and XeF(6), and F(19)-Xe(129) spin-spin coupling constants for XeF(4) and XeOF(4). The data are in accord with reported structures and are similar to values in the literature for chemical shifts of fluorides of neighboring elements.     

Xenon Tetrafluoride: Crystal Structure

On the basis of a three-dimensional x-ray analysis, the xenon tetrafluoride molecule in the solid is planar; the approximate symmetry is D(4h). The average distance between the xenon and the fluorine is 1.92 +/- 0.03 A.     

Xenon Tetrafluoride: Reaction with Aqueous Solutions

Xenon tetrafluoride reacts with water to yield xenon, oxygen, hydrofluoric acid, and a very soluble species containing xenon. Evaporation of the solution yields a white, crystal-line substance which has been identified as xenon (VI) oxide, XeO(3).     

Antiprismatic Coordination about Xenon: The Structure of Nitrosonium Octafluoroxenate(VI)

The structure of nitrosonium octafluoroxenate(VI), 2NOF . XeF(6), has been determined by means of single-crystal x-ray counter methods (R-index = 0.046, weighted R-index = 0.042). The space group is Pnma, with a = 8.914(10) angstroms, b = 5.945(10) angstroms, and c = 12.83(2) angstroms (the numbers in parentheses are the standard deviations to the least significant digit or digits); the calculated density (rho) is 3.354 grams per cubic centimeter, and there are four formula units per unit cell. The material consists of well-separated NO(+) and (XeF(8))(2-) ions; the structural formula is thus (NO)(2) (XeF(8)). The anion configuration is that of a slightly distorted Archimedean antiprism. The observed distortion appears incompatible with a lone-pair repulsion model. Xenon-fluorine bond lengths of 1.971(7), 1.946(5), 1.958(7), 2.052(5), and 2.099(5) angstroms were found.     

Geometry of the Perxenate Ion

A three-dimensional x-ray analylsis of a crystallinie solid of Xe(+8) formed by the reaction of XeF(6) with sodium hydroxide solution indicates that it is sodium perxenate octahydrate, Na(4)XeO(6) * 8H(2)O. The perxenate ion, XeO(6)(-4), has approximately a regular octahedral configuration with a mean xenon-oxygen bond length of 1.875 A.     

南极磷虾粉中氟形态及其分析技术

[目的]建立南极磷虾氟形态分析方法,为南极磷虾的开发利用提供技术支持.[方法]采用逐级化学—超声波浸提技术对南极磷虾粉中氟的赋存形态进行分析研究,并对提取条件进行优化.[结果]南极磷虾粉中氟的赋存形态可分为水溶态氟、可交换态氟、氧化态氟、有机束缚态氟和残渣态氟,分别占总氟的15.7%、17.1%、31.7%、21.5%和14.0%,总氟含量为2518.6 mg/kg,各形态氟含量次序为:氧化态氟>有机束缚态氟>可交换态氟>水溶态氟>残渣态氟.[结论]采用逐级化学—超声波浸提技术能有效地定量研究南极磷虾中氟的赋存形态.     

硒铜镁对黄牛地方性氟病的疗效及其作用机理

32 头地方性氟病黄牛随机分为4 组, 每组8头。1 组为对照组, 饲喂基础日粮, 2～4 组为试验组, 每天饲料中分别添加0.25 m g/kg 硒; 15 m g/kg 铜和0.25 m g/kg 硒 15 m g/kg 铜 1 m g/kg 镁, 连续饲喂83 d, 观察硒铜镁对地方性高氟黄牛体氟排泄的影响。结果表明: 地方性氟病黄牛血硒、血铜含量远低于正常范围的下限, 血氟明显超标。加硒组 (2组) 和加硒铜镁组 (4组) 黄牛血清氟含量第83 天与第0 天以及同期对照组牛相比, 下降极显著 (P< 0.01), 血硒随饲料硒的添加量而上升, 并维持在正常水平, 血铜值反而下降。加铜组 (3 组) 黄牛血清氟含量明显降低 (P< 0.05), 血铜值也随之降低 (P< 0.05), 血硒变化不明显 (P> 0.05)。地方性氟病黄牛添加适量的硒铜镁, 能增加血氟的排出, 提高血硒含量, 但降低了机体的血铜值。揭示硒铜镁能防制动物地方性氟病的发生。     

Xenon as a complex ligand: the tetra xenono Gold(II) cation in AuXe(4)2+(Sb(2)F(11)-)(2)

The first metal-xenon compound with direct gold-xenon bonds is achieved by reduction of AuF(3) with elemental xenon. The square planar AuXe(4)2+ cation is established by a single-crystal structure determination, with a gold-xenon bond length of approximately 274 picometers. The bonding between gold and xenon is of the final sigma donor type, resulting in a charge of approximately 0.4 per xenon atom.     

X-ray Damage to CF3CO2-Terminated Organic Monolayers on Si/Au: Principal Effect of Electrons

The relative importance of x-rays alone and of x-ray-generated primary and secondary electrons in damaging organic materials was explored by use of self-assembled monolayers (SAMs) on multilayer thin-film supports. The substrates were prepared by the deposit of thin films of silicon (0, 50, 100, and 200 angstroms) on thick layers of gold (2000 angstroms). These systems were supported on chromium-primed silicon wafers. Trifluoroacetoxy-terminated SAMs were assembled on these substrates, and the samples were irradiated with common fluxes of monochromatic aluminum K(alpha) x-rays. The fluxes and energy distributions of the electrons generated by interactions of the x-rays with the various substrates, however, differed. The substrates that emitted a lower flux of electrons exhibited a slower loss of fluorine from the SAMs. This observation indicated that the electrons-and not the x-rays themselves-were largely responsible for the damage to the organic monolayer.     

氮肥对茶园土壤氟赋存形态及转化的影响

为研究不同水平氮肥对茶园土壤氟赋存形态及转化的影响,以皖南十字铺茶场红黄壤茶园0~15 cm土壤为对象,设置N0P0K0(CK)、N0P1K1(N0)、N1P1K1(N1)、N2P1K1(N2)、N3P1K1(N3) 5个处理,进行了室内盆钵培养试验,通过分析施肥10、20、30、50、70、90 d后土壤水溶态氟、交换态氟、铁锰结合态氟、有机结合态氟含量、铵态氮含量、土壤pH值,研究施肥对茶园土壤氟赋存形态及转化的影响。结果表明:与CK相比,氮肥与磷钾混施(N1、N2、N3)在短期内(10 d或20 d)使土壤水溶态氟含量降低,交换态氟、铁锰结合态氟、有机结合态氟含量增加,20 d之后土壤水溶态氟增加,交换态氟、铁锰结合态氟、有机结合态氟含量降低,对水溶态氟、交换态氟的影响效果随时间增加而增加,一般施氮量越大影响效果越明显;土壤水溶态氟含量与氮肥施用量成中度正相关,交换态氟与氮肥施用量成中、高度负相关;土壤水溶态氟含量与pH值成极显著高度负相关,交换态氟含量与pH值成极显著高、中度正相关。因此,氮肥在土壤中的转化过程改变了土壤环境pH值,从而影响土壤氟的形态转化和有效性。     

Xenon Hexafluoride: Structure of a Cubic Phase at -80{degrees}C

The crystal structure of a cubic phase of composition XeF(6) has been determined at -80 degrees C. There are no simple molecules in the complex structure which involves 1008 atoms distributed over 1600 positions per unit cell. Ions of XeF(5)+ and F- are associated in tetrameric and hexameric rings of point group symmetries 4 and 32, respectively. The structure contains right-and left-handed conformations of both tetramers and hexamers. The handedness of the tetramers is dis-ordered but the orientation is ordered. The handedness of the hexamers is ordered but the orientation is disordered.     

Melting of two-dimensional solids

Recent theoretical predictions indicate that melting of a two-dimensional solid may be caused by spontaneous creation of dislocations. The theory predicts that melting occurs by a two-step process involving an intermediate phase, called the hexatic phase, in which there is order in the local crystalline axes but not in the positions of atoms. These ideas are being tested by numerical simulations and by experiments on electrons on liquid helium, liquid crystal films, and rare gas layers adsorbed on graphite. Experiments on liquid crystal films indicate that the three-dimensional analog of the hexatic phase exists, and xenon on graphite exhibits a melting transition close to the form predicted.     

Solvated electrons in high-temperature melts and glasses of the room-temperature stable electride [Ca₂₄Al₂₈O₆₄]⁴⁺·4e⁻

Solvated electrons in alkali metal-ammonia solutions have attracted attention as a prototype electronic conductor and chemical reducing agent for over a century. However, solvated electrons have not been realized in a high-temperature melt or glass of an oxide system to date. We demonstrated the formation of persistent solvated electrons in both a high-temperature melt and its glass by using the thermally stable electride [Ca(24)Al(28)O(64)](4+)·4e(-) (C12A7:e(-)) and controlling the partial pressure of oxygen. The electrical and structural properties of the resulting melt and glass differ from those of the conventional C12A7:O(2-) oxide, exhibiting metallic and hopping conduction, respectively, and a glass transition temperature that is ~160 kelvin lower than that of C12A7:O(2-) glass. Solvated electrons reside in cage structures in C12A7:e(-) and form a diamagnetic paired state.     

几种土壤的氟吸附特性研究

采用室内试验方法,研究了4种土壤对氟吸附的特性。结果表明:(1)不同土壤对氟的吸附能力差异很大,随着初始浓度的增大,吸附量明显增大,净吸附量、解吸量也增大,表现为黄壤>红壤>紫色土>石灰土;土壤氟的解吸率随初始浓度的增大而增大,不同土壤间大小次序是石灰土>紫色土>红壤>黄壤。(2)土壤吸附氟后的平衡溶液pH值随氟加入浓度的增大而上升,不同土壤间次序是:石灰土>红壤>紫色土>黄壤。(3)拟合结果表明,Langmuir方程能够较好地拟合土壤对氟的吸附等温线。(4)土壤中氧化物是氟的重要吸附剂,对土壤氟吸附有重要贡献。(5)低分子有机酸对氟吸附的影响一方面表现为阴离子的竞争作用,另一方面表现为酸性条件下的促进作用。     

First-principles calculations of PuO(2+/-x)

The electronic structure of PuO(2+/-x) was studied using first-principles quantum mechanics, realized with the self-interaction corrected local spin density method. In the stoichiometric PuO2 compound, Pu occurs in the Pu(IV) oxidation state, corresponding to a localized f4 shell. If oxygen is introduced onto the octahedral interstitial site, the nearby Pu atoms turn into Pu(V) (f3) by transferring electrons to the oxygen. Oxygen vacancies cause Pu(III) (f5) to form by taking up electrons released by oxygen. At T = 0, the PuO2 compound is stable with respect to free oxygen, but the delicate energy balance suggests the possible deterioration of the material during long-term storage.     

The xenon record of extinct radioactivities in the Earth

Analyses of xenon from well gas rich in carbon dioxide reveal a large excess of radiogenic xenon-129 from the decay of extinct iodine-129. Smaller excesses observed in the heavy xenon isotopes are from fission. These results place narrow limits on any age difference between the earth and the oldest meteorites. The occurrence of excess radiogenic xenon-129 in well gas also suggests that any quantitative degassing of existing solid materials to form the atmosphere must have been limited to a very early period of the earth's history, approximately the first 10(8) years. Alternatively, this observation is consistent with a model of the earth's continuous, but still incomplete, degassing since its time of formation.