Thermochemistry of Li, Na, K, Rb and Cs alkylated phenoxides

Lattice energies and thermochemical radii of the anions OR⁻ (R = 2-Me; 2,6-Me₂; 2,4,6-Me₃; 2,6-t-Bu₂) in alkali metal phenoxides, MOR (M = Li, Na, K, Rb and Cs) were investigated based on the corresponding standard molar enthalpies of formation determined by reaction-solution calorimetry. The results obtained at 298.15 K were as follows: (MOR, cr)/kJ mol⁻¹ = −398.4 ± 1.1 (LiO-2-MePh), −423.4 ± 1.6 (LiO-2,6-Me₂Ph), −457.3 ± 7.1 (LiO-2,4,6-Me₃Ph), −346.6 ± 1.4 (NaO-2-MePh), −399.1 ± 1.5 (NaO-2,6-Me₂Ph), −422.4 ± 7.1 (NaO-2,4,6-Me₃Ph), −496.6 ± 7.1(NaO-2,6-t-Bu₂Ph), −367.8 ± 1.2 (KO-2-MePh), −399.1 ± 1.4 (KO-2,6-Me₂Ph), −368.8 ± 1.2 (RbO-2-MePh), −403.6 ± 1.3 (RbO-2,6-Me₂Ph), −387.0 ± 1.6 (CsO-2-MePh) and −413.6 ± 1.3 (CsO-2,6-Me₂Ph). Estimates of thermochemical raddi, lattice energies and standard enthalpies of formation of not experimentally measured alkali metal phenoxides was successfully done with a model based on the Kapustinskii equation and the set of values experimentally determined.     

ChemInform Abstract: First‐Principles Investigations of the MMgH3 (M: Li,Na, K,Rb, Cs) Series.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

CH_2=CH(XM)(X=S,Se,Te;M=H,Li,Na,K,Rb,Cs,-)的从头算研究

应用相对论有效势在ＭＰ２水平上对ＣＨ２ＣＨ（ＸＭ）（Ｘ＝Ｓ，Ｓｅ，Ｔｅ；Ｍ＝Ｈ，Ｌｉ，Ｎａ，Ｋ，Ｒｂ，Ｃｓ，－）进行了从头计算研究．结果表明，所研究的化合物都有平面式和非平面桥式两种构型．分析了碱金属离子对两可亲核底物ＣＨ２ＣＨＸ－（Ｘ＝Ｓ，Ｓｅ，Ｔｅ）离域化的影响，并用自然布局分析方法（ＮＰＡ）研究了电荷分布的变化，得出了有价值的结论．     

THF-solvated Heavy Alkali Metal Benzyl Compounds (Na,Rb, Cs): Defined Deprotonation Reagents for Alkali Metal Mediation Chemistry

The incorporation of heavy alkali metals into substrates is both challenging and essential for many reactions. Here, we report the formation of THF-solvated alkali metal benzyl compounds [PhCH₂M ⋅ (thf)_n] (M=Na, Rb, Cs). The synthesis was carried out by deprotonation of toluene with the bimetallic mixture n-butyllithium/alkali metal tert-butoxide and selective crystallization from THF of the defined benzyl compounds. Insights into the molecular structure in the solid as well as in solution state are gained by single crystal X-ray experiments and NMR spectroscopic studies. The compounds could be successfully used as alkali metal mediating reagents. The example of caesium showed the convenient use by deprotonating acidic C−H as well as N−H compounds to gain insight into the aminometalation using these reagents.     

用中子活化分析法研究25种元素在人体肝脏亚细胞组分中的分布

采用差速离心分离技术与中子活化分析法（ＮＡＡ）相结合的方法分析了人肝２５５中元素,并用标准参考物保证结果的准确性。分析结果表明,大多数元素在各亚细胞组分中并非均匀分布。Ａｓ、Ａｕ、Ｃｏ、Ｉ、Ｍｇ、Ｓｂ、Ｓｅ在细胞核和线粒体浓度最高。Ａｌ、Ｓｓ、Ａｕ、Ｂａ、Ｆｅ、Ｉ、Ｍｇ、Ｍｏ、Ｓｂ、Ｓｃ在细胞核和线粒体浓度最高。Ａｌ、Ａｓ、Ａｕ、Ｂａ、Ｆｅ、Ｉ、Ｌａ、Ｍｇ、Ｍｎ、Ｓｂ、Ｓｅ在胞液中深度最低,生物体     

Characterization of Heavy Metal Air Pollution in Romania Using Moss Biomonitoring,Neutron Activation Analysis,and Atomic Absorption Spectrometry

ABSTRACT

Heavy metal air pollution in Romania was investigated by using passive moss biomonitoring. This study is a component of an international UNECE ICP Vegetation Program – moss survey. A total of 330 samples of Hypnum cupressiforme, Hylocomium splendens, Pleurozium schreberi, and other mosses were collected in Romania in the summer and autumn of 2010. The concentrations of aluminum, cadmium, chromium, copper, iron, lead, nickel, vanadium, and zinc were determined by graphite furnace/flame atomic absorption spectrometry and instrumental neutron activation analysis. The results were statistically processed to obtain spatial distribution maps of factor scores based on elemental concentrations in the moss, together with the spatial distribution maps of heavy metals in moss. The median concentrations of cadmium, 1.20?mg/kg dry weight, and lead, 30.8?mg/kg dry weight, were high compared with other European countries. The results revealed that the atmospheric deposition of these metals is a problem in north and northwest Romania.     

ChemInform Abstract: Three Alkali Metal Lead Orthophosphates - Syntheses,Crystal Structures and Properties of APbPO4(A:K,Rb, Cs).

Single crystals of the title compounds are prepared by solid state reactions of M₂CO₃ (M: K, Rb, Cs), PbO, PbF₂, H₃BO₃, and (NH₄)H₂PO₄ in a molar ratio of 2:5:5:4:3 (Pt crucible, 700 °C, 10 h).     

Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3H8 (M=K,Rb, and Cs), Mechanisms of Formation,and the Crystal Structure of KB3H8

A facile synthesis of heavy alkali metal octahydrotriborates (MB₃H₈; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF?BH₃, does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH₄/NaBH₄ with THF?BH₃ have to be carried out under reflux. The high stability and solubility of KB₃H₈ were examined, and a crystal structure thereof was obtained for the first time.     

Determination of Trace Elements in Tea and Coffee by Neutron Activation Analysis

Thermal neutron activation analysis, a high-resolution Ge(Li) gamma-ray spectrometer, and an IBM 360/67 digital computer were used to determine the concentration of Na, K, Sc, Cr, Mn, Fe, Co, Cu, Zn, Se, Br, Rb, Sb, Cs, and Hg in ground coffee and tea. This nondestructive multielement technique requires neither pre- nor postirradiation chemistry and eliminates problems of reagent contamination. The method is simple, precise and sensitive to 15 elements. Interferences from fast neutron (n, p) and (n, α) reactions are small and, if necessary, corrections may be applied easily. This technique can be applied to percolated tea and coffee.     

Determination of Silver in Plants by Flameless Atomic Absorption Spectrometry and Neutron Activation Analysis

Abstract

Three analytical techniques suitable for determining silver concentrations in plants are presented and compared. Graphite furnace atomic absorption spectrometry performed directly on sample digests was the most sensitive and convenient. Neutron activation analysis, measuring ^110mAg gave good reproducibility, but lower sensitivity. A cyclic activation scheme to generate and detect the short-lived isotope ¹¹⁰Ag was useful as a quick reconnaissance technique, but interference from ⁷⁶As reduced its effectiveness.

Data are presented on the silver content of terrestrial plants. Background silver concentrations for lichens and bryophytes collected from Wales, U.K. were <0.07μgg^?1. Samples collected from areas contaminated by derelict metal mines contained between 0.1-1.0μAgg^?1. The aerial portions of vascular species usually contained less silver than bryophytes growing on the same substrate. Fungi are shown to bioconcentrate silver to a greater extent than cadmium, copper or lead.     

Thermo‐analytical Investigations on the Superoxides AO2 (A = K,Rb, Cs), Revealing Facile Access to Sesquioxides A4O6

Rb₄O₆ and Cs₄O₆ represent open shell p electron systems, featuring charge, spin, orbital and structural degrees of freedom, which makes them unique candidates for studying the ordering processes related, otherwise exclusively encountered in transition metal based materials. Probing the physical responses has been restrained by the intricacy of synthesizing appropriate amounts of phase pure samples. Tracing the thermal decomposition of respective superoxides has revealed that at least the rubidium and cesium sesquioxides exist in thermodynamic equilibrium, appropriate p‐T conditions given. These insights have paved the way to highly efficient and convenient access to Rb₄O₆ and Cs₄O₆.     

ChemInform Abstract: Crystal Structures of New Alkali Metal-Rich Oxometallates: Rubidium Aluminate Tetrahydroxide,Rb9(AlO4)(OH)4, Rubidium Orthogallate,Rb5GaO4, Cesium bis-Chromate(IV) Oxide,Cs10(CrO4)2O,and Cesium Diindate,Cs8In2O7.

The crystal structures of several new alkali metal oxometallates are determined by single crystal XRD.     

10-30T恒定磁场下碱金属原子的边界轮廓

孤立原子是具有球对称性的.如果将孤立原子置于磁场中,原子的边界半径必然会发生变化.根据原子边界轮廓理论模型,研究和计算了在10~30 T磁场强度下碱金属原子的边界轮廓,可供有关参考.     

Organometallic polymers assembled from cation-pi interactions: use of ferrocene as a ditopic linker within the homologous series [{(Me3Si)2NM}2.(Cp2Fe)]infinity (M=Na, K, Rb, Cs; Cp=cyclopentadienyl)

Addition of ferrocene to solutions of alkali metal hexamethyldisilazides M(HMDS) in arenes (in which M=Na, K, Rb, Cs) allows the subsequent crystallization of the homologous series of compounds [{(Me(3)Si)(2)NM}(2) (Cp(2)Fe)](infinity) (1-4). Similar reactions using LiHMDS led to the recrystallization of the starting materials. The crystal structures of 1-4 reveal the formation of one-dimensional chains composed of dimeric [{M(HMDS)}(2)] aggregates, which are bridged through neutral ferrocene molecules by eta(5)-cation-pi interactions. In addition, compounds 3 and 4 also contain interchain agostic M--C interactions, producing two-dimensional 4(4)-nets. Whereas 1 and 2 were prepared from toluene, the syntheses of 3 and 4 required the use of tert-butylbenzene as the reaction media. The attempted crystallization of 3 and 4 from toluene resulted in formation of the mixed toluene/ferrocene solvated complexes [{(Me(3)Si)(2)NM)(2)}(2) (Cp(2)Fe)(x)(Tol)(y)](infinity) (in which M=Rb, x=0.6, y=0.8, 5; M=Cs, x=0.5, y=1, 6). The extended solid-state structures of 5 and 6 are closely related to the 4(4)-sheets 3 and 4, but are now assembled from a combination of cation-pi, agostic, and pi-pi interactions. The charge-separated complex [K{(C(6)H(6))(2)Cr}(1.5)(Mes)][Mg(HMDS)(3)] (15) was also structurally characterized and found to adopt an anionic two-dimensional 6(3)-network through doubly eta(3)-coordinated bis(benzene)chromium molecules. DFT calculations at the B3 LYP/6-31G* level of theory indicate that the binding energies of both ferrocene and toluene to the M(HMDS) dimers increases in the sequence Li相似文献   

Determination of Selenium and Tin in Human Brain by Graphite Furnace Atomic Absorption Spectrometry

 A method is reported for measuring Se and Sn in human brain tissue. The patients from whom the samples were taken had no diseases in their central nervous system. Microwave energy was applied to digest the brain samples. The digested samples were analyzed without dilution by transversely heated graphite atomizer for atomic absorption spectrometry with longitudinal Zeeman background correction. The dependence of integrated absorbance on various chemical modifiers has been examined. The most appropriate technique proved to be 5 μl sample injection using 20 μg prereduced palladium-nitrate for Se determination, and 20 μl sample injection applying 10 μg palladium-nitrate + 3 μg magnesium-nitrate for the measurements of Sn. The optimal temperature program was found to be 1200 °C pyrolysis and 2100 °C atomisation temperature for Se and 1500 °C pyrolysis and 2300 °C atomisation temperature for Sn. Accuracy of the applied techniques was tested by the analysis of standard reference materials. The precision was ±5% for Se and ±10% for Sn. The range of recovery values was 85–95% for Se and 95–105% for Sn. The mean Se concentrations in the investigated brain parts ranged from 200 to 700 ng/g, while the Sn concentrations were between 20 and 300 ng/g dry weight. Received October 3, 2000. Revision February 1, 2001.