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排序方式: 共有101条查询结果,搜索用时 375 毫秒
41.
Arnold PL Zlatogorsky S Jones NA Carmichael CD Liddle ST Blake AJ Wilson C 《Inorganic chemistry》2008,47(19):9042-9049
The d (0) yttrium N-heterocyclic carbene compound YL 3 (L = OCMe 2CH 2[C{N(CHCH)NPr ( i )}]) has been made and structurally characterized. It adopts a mer configuration of the three bidentate ligands. A comparison of this with the isostructural d (1) titanium complex TiL 3 is made in order to seek experimental evidence of a pi-bonding contribution to the M-C bond. This has been augmented by DFT calculations. Experimentally, the metal radius-corrected Ti-C distance is shorter than the Y-C distance, suggesting a pi-bonding contribution in the d (1) complex, but the computational data suggest that a shorter sigma bond might simply be formed by the more strongly polarizing titanium cation. From the potassium reduction of TiL(OPr ( i )) 3, only a byproduct arising from silicone grease activation was isolable, identified as a mixed-valent, multinuclear, d (0)/d (1) cluster [Ti (III)L 2{Pr ( i )OSiMe 2O}K 2OTi (IV)(OPr ( i )) 4] 2 in which the carbene ligands are bound to the Ti (III) centers in preference to Ti (IV), with longer Ti-C distances than those found in TiL 3. 相似文献
42.
Uranium turnings react with elemental iodine in diethyl ether at room temperature, with sonication and/or stirring, over a period of days to afford UI 3, UI 4(OEt 2) 2, or UI 4(OBu (n) 2) depending on the stoichiometry or ether solvent. This is the first room temperature, and thus safe and convenient, synthesis of UI 3. 相似文献
43.
C Vidalakis J E Tookey J Sommerville 《The Journal of the Operational Research Society》2013,64(8):1194-1204
The delivery of construction projects is typically an assembly operation involving a high number of subassemblies and materials brought on site by the supply chain. However, although supply chain management in construction has attracted significant attention, paradoxically little focus has been placed on construction supply networks and operations. This paper places emphasis on supply chain operations by looking at the logistics function of construction material suppliers. Specifically, the paper examines the impact of demand uncertainty on supply chain performance in order to assess the capacity of material distribution companies to provide a timely and cost-efficient service to the construction industry. The study adopts a discrete event simulation approach to assess the impact of demand fluctuations on two crucial logistics performance measures; lead time and cost efficiency. The results show that lead times are particularly sensitive to fluctuations under conditions of low demand. The findings also reveal that, although transport is a significant cost element for lower demand levels, higher inventory costs result in a negative exponential relationship between increasing demand and cost efficiency. 相似文献
44.
N-Heterocyclic carbenes (NHCs) can bind as two-electron sigma-donor ligands to lanthanide and actinide metal cations. In this review we summarise how the incorporation of an anionic group (alkoxide or amido), to form heterobidentate NHC ligands, allows the synthesis of a range of f-block NHC adducts. The tethering group also allows the lability of the NHC group, and its subsequent reactivity, to be studied. We include a brief survey of the known, structurally characterised f-element-NHC bond distances, and a range of substrates that react to displace the metal-bound NHC group. 相似文献
45.
Arnold PL 《Chemical communications (Cambridge, England)》2011,47(32):9005-9010
Molecular complexes of uranium are capable of activating a range of industrially and economically important small molecules such as CO, CO(2), and N(2); new and often unexpected reactions provide insight into an element that needs to be well-understood if future clean-energy solutions are to involve nuclear power. 相似文献
46.
47.
Polly L. Arnold Ian J. Casely Sergey Zlatogorsky Claire Wilson 《Helvetica chimica acta》2009,92(11):2291-2303
The use of tetravalent cerium alkoxides, nitrates, and triflates was studied as a direct route to [CeIV(carbene)] complexes. Protonolysis reactions between 1H‐imidazolium‐ or imidazoline (=4,5‐dihydro‐1H‐imidazole)‐containing alkoxide proligands HL (L=OCMe2CH2[1‐C(NCHCHNiPr)]) and HLS (LS=OCMe2CH2[1‐C(NCH2CH2NiPr)]) and CeIV tert‐butoxide, triflate, and nitrate compounds were studied to target [CeIV(N‐heterocyclic carbene)] complexes (of unsaturated and saturated carbenes, resp.). Instead, tetravalent cerium imidazolium [(OtBu)3Ce(μ‐OtBu)2(μ‐HL)Ce(OtBu)3], or imidazolinium adducts [(OtBu)3Ce(μ‐OtBu)2(μ‐HLS)Ce(OtBu)3] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL4], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation‐state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL4]. 相似文献
48.
Polly A. Berseth 《Journal of Physics and Chemistry of Solids》2008,69(9):2141-2145
Mixtures of light-weight hydrides and elements were investigated to increase the understanding of the chemical reactions that take place between various materials. This report details investigations we have made into mixtures that include NaAlH4, LiAlH4, MgH2, Mg2NiH4, alkali(ne) hydrides, and early third row transition metals (V, Cr, Mn). Experimental parameters such as stoichiometry, heat from ball milling versus hand milling, and varying the temperature of high pressure molten state processing were studied to examine the effects of these parameters on the reactions of the complex metal hydrides. 相似文献
49.
50.
Pressure sensitive adhesive tape (brown parcel tape) is employed in a great many criminal activities such as the restraint of individuals during robbery and offences against the person, the enclosure of explosive devices and the packaging and concealment of controlled drugs. Packaging materials are ubiquitous in modern society and are produced in such vast quantities that it is increasingly difficult to distinguish between different products or to link materials to a common source. This study demonstrates the potential of stable isotope ratio mass spectrometry to characterise parcel tapes based on a number of properties. The carbon isotopic signature, derived from the substrate polymer, associated additives and adhesive is highly characteristic of a particular tape and allows samples from different sources to be readily distinguished. Further discrimination may be achieved by the incorporation of deuterium and oxygen isotopic data and by analysis of the isolated backing polymer. Recovery of intact tape from simulated forensic samples proved straightforward and the isotopic signature of the tape did not appear to be affected by adverse storage conditions. 相似文献