Chemical Bonding in Homoleptic Carbonyl Cations [M{Fe(CO)5}2]+ (M=Cu,Ag, Au)

Syntheses of the copper and gold complexes [Cu{Fe(CO)₅}₂][SbF₆] and [Au{Fe(CO)₅}₂][HOB{3,5-(CF₃)₂C₆H₃}₃] containing the homoleptic carbonyl cations [M{Fe(CO)₅}₂]⁺ (M=Cu, Au) are reported. Structural data of the rare, trimetallic Cu₂Fe, Ag₂Fe and Au₂Fe complexes [Cu{Fe(CO)₅}₂][SbF₆], [Ag{Fe(CO)₅}₂][SbF₆] and [Au{Fe(CO)₅}₂][HOB{3,5-(CF₃)₂C₆H₃}₃] are also given. The silver and gold cations [M{Fe(CO)₅}₂]⁺ (M=Ag, Au) possess a nearly linear Fe-M-Fe’ moiety but the Fe-Cu-Fe’ in [Cu{Fe(CO)₅}₂][SbF₆] exhibits a significant bending angle of 147° due to the strong interaction with the [SbF₆]⁻ anion. The Fe(CO)₅ ligands adopt a distorted square-pyramidal geometry in the cations [M{Fe(CO)₅}₂]⁺, with the basal CO groups inclined towards M. The geometry optimization with DFT methods of the cations [M{Fe(CO)₅}₂]⁺ (M=Cu, Ag, Au) gives equilibrium structures with linear Fe-M-Fe’ fragments and D₂ symmetry for the copper and silver cations and D_4d symmetry for the gold cation. There is nearly free rotation of the Fe(CO)₅ ligands around the Fe-M-Fe’ axis. The calculated bond dissociation energies for the loss of both Fe(CO)₅ ligands from the cations [M{Fe(CO)₅}₂]⁺ show the order M=Au (D_e=137.2 kcal mol⁻¹)>Cu (D_e=109.0 kcal mol⁻¹)>Ag (D_e=92.4 kcal mol⁻¹). The QTAIM analysis shows bond paths and bond critical points for the M−Fe linkage but not between M and the CO ligands. The EDA-NOCV calculations suggest that the [Fe(CO)₅]→M⁺←[Fe(CO)₅] donation is significantly stronger than the [Fe(CO)₅]←M⁺→[Fe(CO)₅] backdonation. Inspection of the pairwise orbital interactions identifies four contributions for the charge donation of the Fe(CO)₅ ligands into the vacant (n)s and (n)p AOs of M⁺ and five components for the backdonation from the occupied (n-1)d AOs of M⁺ into vacant ligand orbitals.     

一种多元杜瓦引线结构和工艺研究

主要介绍了一种散状引线结构形式的探测器用杜瓦结构及密封封接工艺方法。通过寿命跟踪考核、高灵敏度检漏等各项性能检测,表明这一工艺先进可行并已达到实用化推广的水平。     

多层多屏绝热液氦杜瓦传热分析

分析了不同液氦杜瓦结构,指出多屏多层的杜瓦的优缺点。通过对多屏多层绝热中不同传热方式的逐个分析,建立了一个理论传热模型。依照模型采用数值分析的方式,对多层层数为100层时的传热进行了分析,获得传导冷屏分布方式对传热流密度的影响曲线,并指出多层多屏分布的优化应同时考虑空间和温度两个因素。     

制冷机冷却型超导磁体杜瓦的研制

介绍了带制冷机冷却的超导磁体系统杜瓦的设计、制作及实验结果分析。杜瓦采用 4 0 K、10 K双制冷屏结构 ,其室温磁场孔径为 75 mm,长 4 15 m m。试验结果为 :液氦蒸发率为 0 .6 9升 /天 (在 2 0天连续试验期内 ) ,优于合同规定的指标 (2 .4升 /天 )。双制冷屏由一台双级 G- M制冷机冷却 ,工作时一级冷屏温度为 35 K,二级冷屏温度为 7.0 K。磁体系统的磁场强度为 3T,满足了用户的使用要求     

Hexamethyl(Dewar Benzene) (Hexamethylbicyclo[2.2.0]hexa-2,5-diene)

Hexamethyl(Dewar benzene) was first obtained by bicyclotrimerization of 2-butyne in the presence of aluminum chloride. This preparation provided a basis for a comprehensive study of the chemical reactivity of Dewar benzene derivatives. Interesting information concerning the reactivity of the permethylated Dewar benzene system can be deduced from its behavior on hydrogenation and oxidation, and, in particular, from the addition of H-acidic compounds and from the substitution and elimination reactions of the resulting adducts.     

Gas-phase enthalpies of formation of the fluorobenzenes family and their dewar isomers from ab initio calculations

The standard gas-phase enthalpies of formation, at T = 298.15 K, of the complete series of fluorobenzene and their corresponding dewar isomers have been determined by means of the CBS-QB3 and G3MP2B3 composite approaches. These values have been estimated by using appropriate supporting reactions, such as, reactions of atomization or of atom substitution. The results show that there is a linear dependence between the enthalpy of the most stable n-fluorobenzene and the corresponding n-fluorodewar benzene (n = 0, 1, …, 6). Further, the estimates are always more negative than the experimental results and so, suggested enthalpies of formation for 1,2,3-, 1,2,4- and 1,3,5-trifluorobenzenes and for 1,2,3,4- and 1,2,3,5-tetrafluorobenzenes are those retrieved from G3MP2B3 calculations added by 8 kJ/mol. The interaction of four different M⁺ ions with fluorobenzene and the three difluorobenzenes shows that the σ-interaction with 1,2-difluorobenzene is stronger than π-interaction on these fluorobenzenes.     

Synthesis and crystal structure of 1,2,4-trifluoro-3,5,6-tris(triisopropylsilyl)benzene

Fluorinated Dewar benzene (1,2,4-trifluoro-3,5,6-tris(triisopropylsilyl)bicyclo[2,2,0]-hexa-2,5-diene) efficiently prepared from fluoro(triisopropylsilyl)acetylene was thermochemically or photochemically transformed into the corresponding highly crowded fluorinated benzene (1,2,4-trifluoro-3,5,6-tris(triisopropylsilyl)benzene) in excellent yield. The molecular structure of the crowded benzene was determined by X-ray crystallography.     

一种非致冷红外探测器真空封装的研究

介绍了一种非致冷红外探测器杜瓦组件的封装设计;对探测器件在真空封装过程中的关键工艺技术进行了比较深入的分析;阐述了影响组件真空寿命及可靠性的因素以及解决措施。     

A systematic study of stereochemical effects in homologous poly(alkenamer)s: Dewar benzene versus norbornene

Two diastereomeric derivatives of norbornene, dimethyl (1R,2R,3S,4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate and dimethyl (1R,2S,3S,4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate, were synthesized and polymerized using ring-opening metathesis polymerization (ROMP). For comparative purposes, diastereomeric derivatives of Dewar benzene, dimethyl (1R,2S,3R,4S)-bicyclo[2.2.0]hex-5-ene-2,3-dicarboxylate and dimethyl (1R,2S,3S,4S)-bicyclo[2.2.0]hex-5-ene-2,3-dicarboxylate, were also synthesized and polymerized using ROMP. The polymerization reactions proceeded in a controlled manner as evidenced in part by linear relationships between the monomer-to-catalyst feed ratios and the molecular weights of the polymer products. Chain extension experiments were also conducted which facilitated the formation of block copolymers. Although the poly(norbornene) derivatives exhibited glass transition temperatures that were dependent on their monomer stereochemistry (cis: 115°C vs. trans: 125°C), more pronounced differences were observed upon analysis of the polymers derived from Dewar benzene (cis: 70°C vs. trans: 95°C). Likewise, microphase separation was observed in block copolymers that were prepared using the diastereomeric monomers derived from Dewar benzene but not in block copolymers of the norbornene-based diastereomers. The differential thermal properties were attributed to the relative monomer sizes as reducing the distances between the polymer backbones and the pendant stereocenters appeared to enhance the thermal effects.