铍的夹心和半夹心化合物中铍原子的共价

用DV-XαSCC方法和自然键轨道法研究了CpBeH和Cp_2Be的电子结构和成键情况,进而根据作者之一提出的共价定义研究了CpBeX(X=H,Cl,Br,CH_3,C≡CH,……)和Cp_2Be等化合物中铍原子的共价.结果表明,在这些化合物中,铍原子的共价均为6.     

铍的夹心和半夹心化合物中铍原子的共价

用DV-XαSCC方法和自然键轨道法研究了CpBeH和Cp2Be的电子结构和成键情况,进而根据作者之一提出的共价定义研究了CpBeX(X=H, Cl, Br, CH3, C≡CH, ...)和Cp2Be等化合物中铍原子的共价。结果表明, 在这些化合物中, 铍原子的共价均为6。     

炔烃桥和氢桥铍化合物中铍原子的共价

根据作者之一提出的共价的新定义，用DV－X_αSCC和自然健轨道法研究了[MeBe(C≡CMe)NMe_3]_2，[Be(C≡CR)_2]_n，[MeBeH·NMe_3]及(BeH_2)_n等化合物中铍原子的共价．结果表明，在这几种化合物中铍原子的共价都是6．     

铍的快速测定——铍试剂Ⅲ比色法测定铍方法改进

地质找矿中,铍的测定,多采用铍试剂Ⅲ比色法,此法具有灵敏度高,显色溶液稳定等优点。其不足之处:诸如沉淀除硅,分离干扰等,手续繁杂、费时、重现性欠佳、成本较高。为解决生产中存在的问题,我们本着实践-认识-再实践-再认识的精神,对铍试剂Ⅲ比色法作了一些改进;试样经氢氧化钠-氯化钠熔融,水浸取,分离铁等、氢氧化物沉淀,铍、钨(铍、钨都具有“亲石”性,且常伴生)分别呈铍酸钠、钨酸钠留在溶液里。在pH>12的试液里,EDTA-NTE掩蔽干扰离子,铍不被EDTA-NTE络合,硅、氟、硼不干扰,铍和铍试剂Ⅲ形成红紫色络合     

肺癌与铍

铍是轻金属元素 ,又是稀有元素 ,人们对它还不太熟悉。有意思的是铍的化合物还有点甜味。铍是毒性最强的金属元素之一。据研究 ,每一立方米的空气中只要含有一毫克的铍尘 ,便能使人马上得急性肺炎 ,而且死亡率相当高。国外有关铍中毒的报道很多 ,例如 ,美国的马萨诸塞州荧光灯制造厂 ,从 1 94 1年就发现有呼吸困难、类似结核病的患者 ,此后陆续发生 ,而且该厂肺癌的发病率也高。查其原因 ,是因为该厂用铍的硅酸盐作为荧光体 ,引起铍中毒。铍化合物也是有毒的 ,铍离子与细胞核有强烈的亲和性 ,对各种酶类的活性有阻碍作用。长期吸入铍或铍化…     

微量铍的示波极谱测定

本文介绍了铍与铍试剂Ⅱ络合物的极谱特性.在氢氧化铵介质中,铍与铍试剂Ⅱ生成电活性络合物.1:1的铍/铍试剂Ⅱ络合物在-0.80伏(对饱和甘汞电极)有一灵敏的吸附波.最适宜的支持电解质为4％EDTA-0.8N NH_4 OH-0.5N NH_4Cl-0.002％铍试剂Ⅱ.铍的测定范围为1.5×10(-8)M-1×10(-5)M.研究了干扰情况.     

铍-铬天青S-两性-非离子混合表面活性剂显色反应研究及其应用

研究了在癸基二甲基氨基乙酸-非离子混合型表面活性剂存在下,Be(Ⅱ)-CAS的显色反应和光度特性,其中,Be(Ⅱ)CAS-DEDMAA-Tween-80显色体系的λ_(max)=614 nm,ε_(614)=1.20×10~5;铍量在0—1.5 ug/25mL范围服从比尔定律。方法可用于铜合金中微量铍的直接测定。     

中国煤中铍的分布赋存特征研究

根据对中国不同矿区1018个煤层煤样和生产煤样铍含量数据的统计结果,分析了中国不同成煤时代、不同聚煤区煤中铍的分布特征。同时,根据对10个不同煤田煤样的实验室浮沉试验、煤岩分析等试验研究,运用Solari方法,计算了煤中各组分中铍的理论含量,讨论了中国煤中铍的赋存特征,尤其是铍在各种煤岩组分中的分布。研究表明,铍在煤中富集程度较高,但相对于世界煤中平均水平来说,中国煤中铍含量总体水平较低。煤中铍主要赋存于惰质组及伊利石粘土矿物中,在镜质组及其它矿物中含量较低。同时,中国大多数煤中铍的有机亲和性指数较高,不利于选煤过程中铍的脱除。     

铍的荧光光度分析进展

铍是常见的合金元素之一,它可使合金的抗氧化、抗腐蚀及耐磨作用增强.同时,铍在原子能工业,电子工业及航天器材等方面也都有应用,因而铍的各种分析检测方法受到工业与环保等部门的重视.荧光光度法具有灵敏度高,设备与操作简便等特点,更受分析工作者关注.近10年来,铍的荧光分析有了一些新进展,研究了一些新试剂、新体系及新技     

铍的萃取分离

近年来由于铍在原子能和火箭技术中找到了新的用途,因之铍的分析分离问题已引起了人们极大的兴趣。本文拟就近十年来有关溶剂萃取分离铍的方法的研究作一综述。螯合物体系β-二酮类:铍与β-二酮类的乙酰丙酮(简称 AA)、苯酰丙酮、二苯酰甲烷、2-麸酰-苯酰甲烷、2-麸酰-2-噻吩甲酰甲烷等能形成稳定的螯合物。尤特(vanUitert)等已测得了这些螯合物的生成常数。另外铍与硫茂羧基三氟丙酮(简称TTA)也能生成在低的     

Novel binding of beryllium to dicarboxyimidazole-based model compounds and polymers

The ligand 4,5-dicarboxyimidazole (H(2)DCI) and its methyl derivative 1-methyl-4,5-dicarboxyimidazole (H(2)MDCI) have been shown to bind to Be(II) forming a zwitterionic species that has been structurally characterized. A new dicarboxyimidazole-based polymer has been prepared and its Be-binding properties have been studied using NMR ((1)H and (9)Be) and fluorescence spectroscopy; it represents a rare example of beryllium binding to a polymer. Models of the mononuclear and polymeric Be(II)-binding sites have been studied using density functional theory (DFT), and the (9)Be NMR chemical shifts of these model materials have been calculated for the purpose of direct comparison to experimentally observed values. Differences in the binding modes of the mononuclear and polymeric species are discussed.     

Ultrashort Beryllium−Beryllium Distances Rivalling Those of Metal−Metal Quintuple Bonds Between Transition Metals

Chemical bonding is at the heart of chemistry. Recent work on high bond orders between homonuclear transition metal atoms has led to ultrashort metal?metal (TM?TM) distances defined as d_M?M<1.900 Å. The present work is a computational design and characterization of novel main group species containing ultrashort metal?metal distances (1.728–1.866 Å) between two beryllium atoms in different molecular environments, including a rhombic Be₂X₂ (X=C, N) core, a vertical Be?Be axis in a 3D molecular star, and a horizontal Be?Be axis supported by N‐heterocyclic carbene (NHC) ligands. The ultrashort Be?Be distances are achieved by affixing bridging atoms to attract the beryllium atoms electrostatically or covalently. Among these species are five global minima and one chemically viable diberyllium complex, which provide potential targets for experimental realization.     

Dative bonds versus electron solvation in tri‐coordinated beryllium complexes: Be(CX)3 [X = O,S, Se,Te, Po] and Be(PH3)3 versus Be(NH3)3

The formation mechanism and bonding scheme for the titled molecules is proposed based on high‐level theoretical calculations. All species are formed via three dative bonds from the ligands to Be. For Be(CX)₃ [X = O, S, Se, Te, Po] species and Be(PH₃)₃ the two electrons of beryllium are promoted from 2s to 2p facilitating these bonds. At the same time, electronic density is donated toward the ligands via the π‐frame. In contrast, ammonia partly solvates the valence 2s electrons of Be, which are delocalized in the periphery of the molecule. Based on the proton affinity of all of these complexes and their derivatives, we found that they are strong Lewis bases. For example, Be(PMe₃)₃ is stronger than ammonia and its ethyl substituted analogue and could serve as the basis of more efficient frustrated Lewis pairs.     

Key Role of Intramolecular Metal Chelation and Hydrogen Bonding in the Cobalt‐Mediated Radical Polymerization of N‐Vinyl Amides

This work reveals the preponderance of an intramolecular metal chelation phenomenon in a controlled radical polymerization system involving the reversible trapping of the radical chains by a cobalt complex bis(acetylacetonato)cobalt(II). The cobalt‐mediated radical polymerization (CMRP) of a series of N‐vinyl amides was considered with the aim of studying the effect of the cobalt chelation by the amide moiety of the last monomer unit of the chain. The latter reinforces the cobalt? polymer bond in the order N‐vinylpyrrolidone<N‐vinyl caprolactam<N‐methyl‐N‐vinyl acetamide, and is responsible for the optimal control of the polymerizations observed for the last two monomers. Such a double linkage between the controlling agent and the polymer, through a covalent bond and a dative bond, is unique in the field of controlled radical polymerization and represents a powerful opportunity to fine tune the equilibrium between latent and free radicals. Possible hydrogen bond formation is also taken into account in the case of N‐vinyl acetamide and N‐vinyl formamide. These results are essential for understanding the factors influencing Co? C bond strength in general, and the CMRP mechanism in particular, but also for developing a powerful platform for the synthesis of new precision poly(N‐vinyl amide) materials, which are an important class of polymers that sustain numerous applications today.     

N-甲基-N-(2-甲基丙烯酰氧乙基)苯胺与其聚合物的荧光光谱

<正> 我们曾报道过甲基丙烯酸-4-N,N-二甲氨基苄酯(DMABMA)、N-(4-N′N′-二甲氨基苯基)代丙烯酰胺(DMAPMA)、8-丙烯酰氧喹啉(AQ)、N-丙烯酰-N′-苯基哌嗪(APP)等在同一分子中含有缺电子双键和给电子发色基团的单体及它们的聚合物在溶液中的荧光行为。在相同的链节克分子浓度下,这些单体的荧光强度比其聚合物的荧光强度低很多。我们将这种现象称为“结构自猝灭现象”。这种现象是由于共存在这类     

The ionization energy of Be2, and spectroscopic characterization of the (1)3Sigmau+, (2)3Pig, and (3)3Pig states

Low lying electronic states of the beryllium dimer were investigated by laser induced fluorescence (LIF) and resonance enhanced multiphoton ionization (REMPI) techniques. Be(2) was formed by pulsed laser ablation of Be metal in the presence of helium carrier gas, followed by a free jet expansion into vacuum. Several previously unobserved states of the dimer were characterized. These included transitions of the triplet manifold (2)(3)Pi(g) <-- (1)(3)Sigma(u)+ and (3)(3)Pi(g) <-- (1)(3)Sigma(u)+, for which rotationally resolved bands were obtained. In addition, transitions to the v' = 10-18 vibrational levels of the A (1)Pi(u) state were recorded. Photoionization efficiency (PIE) measurements were used to determine an accurate ionization energy (IE) for Be(2) of 7.418(5) eV and the term energy for (1)(3)Sigma(u)+. Above the ionization threshold the PIE spectrum was found to be highly structured, consisting of overlapping Rydberg series that converged on excited vibrational levels of Be(2)+. Analysis of these series yielded a vibration frequency for the X(2)Sigma(u)+ state of 498(20) cm(-1). The bond dissociation energy for Be(2)+, deduced from the IE measurement, was 16 072(40) cm(-1). Multi-reference configuration interaction (MRCI) calculations were carried out for Be(2) and Be(2)+, yielding results that were in excellent agreement with the experimental observations.     

Metal coordination polymers. III. Molecular weights of beryllium phosphinate polymers in chloroform

Vapor-phase osmometric molecular weight measurements on beryllium di-n-butyl-phosphinate are in general agreement with the results obtained in chloroform by Ripamonti and co-workers. The degree of polymer association in anhydrous chloroform is approximately twice that obtained in reagent-grade chloroform, and the values obtained in both types of chloroform are higher than those obtained by Ripamonti. Membrane osmometric molecular weight measurements on beryllium 4-biphenyl (phenyl)-phosphinate in chloroform indicate a reversible degradation exists between a number-average molecular weight of 170 000 and 30 000, with the value dependent upon the polymer concentration. Treatment of chloroform solutions of this polymer with ammonia prevents reassembly of the polymer from 30 000 to higher values. To explain this and other solution properties of this polymer, a structure is proposed which involves endgroup hydrogen bonding of phosphinate-bonded aggregates containing approximately 50 monomer units (M _n = 30 000). Under certain conditions, the hydrogen-bonded aggregates may contain up to 300 monomer units, but in polar solvents such as water or chloroform they are rapidly degraded.     

键函数法与Be2体系的稳定性1: Be2的基态

采用价电子全CI(FCI)方法对Be2的基态(X^1∑g^+)进行了研究, 仔细考察了键函数在弱键体系计算中的作用。对引入键函数的不同方式分别按Boys方法计算了基组重叠误差(BSSE)。键函数的运用使得Be2基态性质的计算结果大为改善。研究结果表明键函数方法在相互作用能小的体系的计算中十分可取。     

Geometry and stability of BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters

Density functional theory B3PW91/6-31+G* calculations on BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters have been carried out to examine the effect of cluster size, relative composition, binding energy per atom, HOMO-LUMO gap, vertical ionization potential, and electron affinity on their relative stabilities. The most stable planar cyclic conformations of these clusters always show at least a set of two carbon atoms between two beryllium atoms, while structures where beryllium atoms cluster together, or allow the intercalation of one carbon atom between two of them, generally seem to be the least stable ones. Clusters containing 1, 2, and 3 beryllium atoms (Be2C8, Be3C6, Be2C6, BeC6, Be2C4, BeC4, Be2C2, and BeC2) are identified as clusters of "magic numbers" in terms of their high binding energy per atom, high HOMO-LUMO gap, vertical ionization potential, and second difference in energy per beryllium atom.