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501.
Binuclear complexes [M2Cl4(-bpym)], where M = VO2+, FeII, CoII or CuII and bpym = 2,2-bipyrimidine, and [M2(hfacac)4(-bpym)] complexes, where hfacac = hexafluoroacetylacetonate and M = FeII, NiII or CoII have been synthesized and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r spectroscopies and by magnetic susceptibility measurements (in the 4.2–291K range). CoII and FeII are in a high spin state. [(VO)2Cl4(-bpym)] is paramagnetic, without significant interactions. [Fe2Cl4(-bpym)] shows a singular behaviour explained by an antiferromagnetic intradimer exchange and a ferromagnetic interdimer interaction. All other complexes are antiferromagnetic, with an intramolecular exchange parameter, J, varying from –3.3 cm–1 for CoII/math> to –109 cm–1 for CuII.  相似文献   
502.
A new mixed oxaaza‐macrocyclic ligand, L1, has been obtained by direct synthesis between 1,4‐bis‐(2′‐formylphenyl)‐1,4‐dioxabutane and the diamine 2,2′‐ethylenedioxydiethylamine. The dialkylated ligand L2, bearing two nitrobenzyl pendant groups, has been prepared and transitional, post‐transitional and Ca2+, Sr2+, and Ba2+ metal complexes have been synthesized in order to elucidate the coordination preferences. The crystal structures of the ligands L1 and L2 and the complexes [SrL2(H2O)2](ClO4)2 and [BaL2(NCS)2(CH3CN)]·CH3CN have been determined by single crystal X‐ray diffraction. The structures reveal the presence of mononuclear endomacrocyclic complexes where the pendant arms radiate away from the ligand.  相似文献   
503.
We have examined the leachability of the toxic elements cadmium, arsenic, mercury, and selenium from solid wastes. The solid wastes studied are municipal incinerator ash, coal fly ash, hospital incinerator ash, raw sewage sludge, sewage incinerator bottom ash, and sewage incinerator lagoon ash (which is a combination of bottom and fly ashes). Cadmium displayed the greatest leachability in all waste types, with 76% leached from the municipal refuse incinerator ash. Although the sources of elements in the wastes are diverse, the leachability and hence the bioavailability in the incinerator ash appears mainly determined by the volatility of the element.  相似文献   
504.
A series of poly(-n-alkyl -L-aspartate)s (n being the number of carbon atoms in the linear alkyl side chain, withn=1, 2, 4, 6, 8, 12, 18 and 22), was studied by differential scanning calorimetry and thermogravimetric analysis. The effect of the length of the alkyl group on thermal properties such as stability, melting and crystallization of side chains, was investigated. For the polymers with n12, two endothermic peaks at T1 and T2 were detected separating three distinct phases A, B and C. The peak at T1 corresponds to the melting of the crystallized paraffinic side chains (transition A-B), and the peak: at T2 may be attributed to a transition (B-C), implying a liquid crystal phase.This work has been supported by DGICYT PB-93-0960 and PB-93-1241. F.L.-C. acknowledges financial assistance from the Venezuelan institutions Universidad de Los Andes and Fundayacucho.  相似文献   
505.
The symmetric d(5) trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (dmpe = 1,2-bis(dimethylphosphino)ethane) have been prepared by the reaction of [Mn(dmpe)(2)Br(2)] with two equivalents of the corresponding acetylide LiC triple bond CSiR(3). The reactions of species 1 with [Cp(2)Fe][PF(6)] yield the corresponding d(4) complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)][PF(6)] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu(4)F (TBAF) at -10 degrees C to give the desilylated parent acetylide compound [Mn(dmpe)(2)(C triple bond CH)(2)][PF(6)] (6), which is stable only in solution at below 0 degrees C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(C triple bond CH)][PF(6)] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)(2)(C triple bond CSiR(3))(C=CH(2))] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp(2)Fe][PF(6)] and one equivalent of quinuclidine. The conversion of [Mn(C(5)H(4)Me)(dmpe)I] with Me(3)SiC triple bond CSnMe(3) and dmpe afforded the trans-iodide-alkynyl d(5) complex [Mn(dmpe)(2)(C triple bond CSiMe(3))I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique Mn(III) product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed-valent species [[Mn(dmpe)(2)(C triple bond CH)](2)(micro-C(4))][PF(6)] (11) by C-C coupling of [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [[Mn(dmpe)(2)(C triple bond CSiMe(3))](2)(micro-C(4))][PF(6)] [12](+) is obtained by the reaction of 7 a with one equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The relatively long-lived radical intermediate [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] could be trapped as the Mn(I) complex [Mn(dmpe)(2)(C triple bond CH)(triple bond C-CO(2))] (14) by addition of an excess of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear Mn(II)/Mn(II) compounds [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))] (R = H, 11; R = SiMe(3), 12) are produced by the reduction of [11](+) and [12](+), respectively, with [FeCp(C(6)Me(6))]. [11](+) and [12](+) can also be oxidized with [Cp(2)Fe][PF(6)] to produce the dicationic Mn(III)/Mn(III) species [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))][PF(6)](2) (R = H, [11](2+); R = SiMe(3), [12](2+)). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X-ray diffraction studies have been performed on complexes 4 b, 7 b, 9, [12](+), [12](2+), and 14.  相似文献   
506.
The hybrid imine/amine palladium(II) coordination complexes [PdX2(kappa2-N(imino),N(amino))](X = Cl, AcO; kappa2-N(imino),N(amino)= 4ClC6H4CHNCH2(CH2)nN(CH3)2, n= 1, 2) have been prepared in different isomeric forms which include E/Z arrangement around the C[double bond]N bond of the hybrid ligand and {Pd(kappa(2)-N(imino),N(amino))} ring conformation. The crystal structures of four of them, E-1AcO, Z-1AcO, E-2AcO and E-2Cl, have been determined and the solution behaviour in acetic acid, the common cyclometallating solvent, for all these systems studied. The complexes in acetic acid solution are shown to maintain the structure determined by X-ray crystallography, as they do in deuterated chloroform. Nevertheless, a partial opening equilibrium of the {Pd(kappa2-N(imino),N(amino))} ring is observed by NMR experiments. When the complexes are held in solution for longer periods the corresponding cyclometallated derivatives, 1AcO-CM, 2AcO-CM, 1Cl-CM and 2Cl-CM, containing the {Pd(kappa2-C,N(imino))} palladacycle are obtained, as characterized by 1H NMR spectroscopy. In these compounds the total opening of the N(amino) moiety of the ligand has occurred. The C-H bond activation process has been studied kinetico-mechanistically at different temperatures, pressures and acid concentrations; the results agree with the need of an opening of the chelate ring in [PdX2(kappa2-N(imino),N(amino))] prior to the proper cyclometallation reaction. The values of the enthalpies of activation are higher than those observed for known N-monodentated cyclometallating ligands, as should correspond to the contribution of a ligand dechelation pre-equilibrium. The entropies and volumes of activation are also indicative of this predissociation that include an important amount of contractive ordering. The presence of small amounts of triflic acid in the reaction medium accelerates the reaction to the value observed for N(imino)-monodentate systems, indicating that the full opening of the chelate ring has taken place. For the badly oriented isomeric forms of the ligand in the chelated complex (Z), the cyclometallation process is even more slow and corresponds directly to the reorganization of the ligand to its cyclopalladation-active (E) conformation.  相似文献   
507.
Two isomeric Ru(II) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with Cl and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans,cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2a, and cis(out),cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[Ru(II)Cl(2)(Hbpp)(MeCN)(dmso)], 4. While the 1 e(-) oxidation of 2b or cis(out),cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3b, generates a stable product, the same process for 2a or trans,cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (K(III)(O)(-->)(S) = 0.25 +/- 0.025, k(III)(O)(-->)(S) = 0.017 s(-1), and k(III)(S)(-->)(O) = 0.065 s(-1); K(II)(O)(-->)(S) = 6.45 x 10(9), k(II)(O)(-->)(S) = 0.132 s(-1), k(II)(S)(-->)(O) = 2.1 x 10(-11) s(-1)). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms.  相似文献   
508.
Vitrification phenomena and further structural relaxation processes or physical ageing occurring in the isothermal curing reaction of an epoxy resin are studied by Differential Scanning Calorimetry (DSC). The vitrification time,t v , the limiting conversion degree and the limiting glass transition temperature (T g) are evaluated at curing temperatures (T c) between 30 and 100C. The dependence of limitingT g withT c permits the determination of the maximumT g of the resin (109C). The physical ageing, which appears as the the last step of curing reaction for curing times above to vitrification, is analyzed through the endothermic peak superposed to the glass transition temperature. The results obtained in partially reticulated resin show the kinetics of the physical ageing to slow down asT c increases, as a consequence that the segmental mobility is reduced.
Zusammenfassung VitrifikationphÄnomeme und strukturelle Relaxations-respektive AlterungsvorgÄnge von Epoxiden wurden mitells isothermer DSC Messungen untersucht. Die Vitrifikationszeit, der Grenzwert des Unwandlungsgrades und die Grenztemperatur der Glasumwandlung wurden in Bereich von 30 bis 100C ermittelt. Werden Epoxide für Temperaturen unterhalb der Glasumwandlungstemperatur einer thermischen Behandlung ausgesetzt, so bilden sich SpannungszustÄnde aus, die bei der ErwÄrmung unmittelbar über der Glasumwandlungstemperatur mit einem endothermen Vorgang relaxieren.


Financial support of this work has been provided by CICYT (project No. PBO395/85). Special thanks are addressed to CIBA-GEIGY for supplying the materials.  相似文献   
509.
The dinuclear gem-dithiolato bridged compounds [Rh2(μ-S2Cptn)(cod)2] (1) (CptnS22− = 1,1-cyclopentanedithiolato), [Rh2(μ-S2Chxn)(cod)2] (2) (ChxnS22− = 1,1-cyclohexanedithiolato), [Rh2(μ-S2CBn2)(cod)2] (3) (Bn2CS22− = 1,3-diphenyl-2,2-dithiolatopropane) and [Rh2(μ-S2CiPr2)(cod)2] (4) (iPr2CS22− = 2,4-dimethyl-2,2-dithiolatopentane) dissolved in toluene in the presence of monodentate phosphine or phosphite P-donor ligands under carbon monoxide/hydrogen (1:1) atmosphere are efficient catalysts for the hydroformylation of oct-1-ene under mild conditions (6.8 atm of CO/H2 and 80 °C). The influence of the gem-dithiolato ligand, the P-donor co-catalyst and the P/Rh ratio on the catalytic activity and selectivity has been explored. Aldehyde selectivities higher than 95% and turnover frequencies up to 245 h−1 have been obtained using P(OMe)3 as modifying ligand. Similar activity figures have been obtained using P(OPh)3 although the selectivities are lower. Regioselectivities toward linear aldehyde are in the range 75–85%. The performance of the catalytic systems [Rh2(μ-S2CR2)(CO)2(PPh3)2]/PPh3 has been found to be comparable to the systems [Rh2(μ-S2CR2)(cod)2] at the same P/Rh ratio. The system [Rh2(μ-S2CBn2)(cod)2] (3)/P(OPh)3 has been tested in the hydroformylation-isomerization of trans-oct-2-ene. Under optimized conditions up to 54% nonanal was obtained. Spectroscopic studies under pressure (HPNMR and HPIR) evidenced the formation of hydrido mononuclear species under catalytic conditions that are most probably responsible for the observed catalytic activity.  相似文献   
510.
For different reliability importance measures we prove that the criticality relation between nodes can completely determine the most important component in a system. In particular, we prove that in k-out-of-n systems, the ranking of component reliabilities determines the ranking of component importance for, at least, three different reliability importance measures.  相似文献   
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