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91.
Miroslava Matikov Maarov Juraj ernk Werner Massa 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(5):m187-m189
In the structure of the title salt, (NH4)(C8H20N)2[Fe(CN)6]·3H2O, the O atom of one of the water molecules shares its crystallographic site with the N atom of the ammonium cation in a 1:1 ratio. The second O atom from the two crystallographically independent water molecules is disordered over two positions separated by 0.551 (1) Å. The water molecules and ammonium cations form tetrameric hydrogen‐bonded units that, along with the complex anion, form the hydrophilic part of the structure. The hydrophobic part of the structure, represented by the tetraethylammonium cation, is located in cube‐like cavities of the hydrophilic framework. 相似文献
92.
Summary The equilibrium mechanical behaviour of weak diepoxide-monoepoxide-diamine networks, prepared with an excess of diamine and measured in the rubbery state, was compared with theoretical predictions obtained by using the theory of branching processes. The experimental equilibrium moduli fit well the shape of theoretical curves over a broad range of crosslinking density regardless of whether the contribution by trapped entanglements is considered or not. The data fit equally well the theoretical dependence for the front factor A = 1 without entanglement contribution and forA = (f
e
- 2)/f
e
, (f
e
is the average effective functionality of a junction) with an entanglement contribution based on the contact probability between any two units within elastically active network chains (Langley).Dedicated to Prof. Dr.G. Rehage on the occasion of his 60th birthday.With 5 figures 相似文献
93.
Adiabatic electron affinities, optimized molecular geometries, and IR-active vibrational frequencies have been predicted for small cyclic hydrocarbon radicals C(n)H(2)(n)(-)(1) (n = 3-6) and their perfluoro counterparts C(n)F(2)(n)(-)(1) (n = 3-6). Total energies and optimized geometries of the radicals and corresponding anions have been obtained using carefully calibrated (Chem. Rev. 2002, 102, 231) density functional methods, namely, the B3LYP, BLYP, and BP86 functionals in conjunction with the DZP++ basis set. The predicted electron affinities show that only the cyclopropyl radical tends to bind electrons among the hydrocarbon radicals studied. The trend for the perfluorocarbon (PFC) radicals is quite different. The electron affinities increase with expanding ring size until n = 5 and then slightly decrease at n = 6. Predicted electron affinities of the hydrocarbon radicals using the B3LYP hybrid functional are 0.24 eV (C(3)H(5)/C(3)H(5)(-)), -0.19 eV (C(4)H(7)/C(4)H(7)(-)), -0.15 eV (C(5)H(9)/C(5)H(9)(-)), and -0.11 eV (C(6)H(11)/C(6)H(11)(-)). Analogous electron affinities of the perflurocarbon radicals are 2.81 eV (C(3)F(5)/C(3)F(5)(-)), 3.18 eV (C(4)F(7)/C(4)F(7)(-)), 3.34 eV (C(5)F(9)/C(5)F(9)(-)), and 3.21 eV (C(6)F(11)/C(6)F(11)(-)). 相似文献
94.
Fattakhova Rohlfing D Rathouský J Rohlfing Y Bartels O Wark M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):11320-11329
Mesoporous silica thin films were shown to be an appropriate matrix for immobilization of discrete electroactive moieties, yielding uniform transparent thin film electrodes with defined texture and enhanced electrochemical activity. The mesoporous silica films prepared on conducting FTO-coated glass substrate were postsynthetically functionalized. Alkoxysilanes were used as precursors for subsequent grafting via ionic or covalent bonds of representative electroactive species, such as polyoxometalate PMo12O(40)3-, hexacyanoferrate(III), and ferrocene. The electrochemically active concentration within the silica-based composite electrodes achieves 90, 260, and 60 micromol cm(-3) for polyoxometalate, hexacyanoferrate(III), and ferrocene, respectively. The amount of molecules involved in the charge-transfer sequence is proportional to the film thickness and comparable to the total amount of embedded guests. Thus, eventually the whole bulk volume of the modified silica films is electrochemically accessible. Immobilization in the chemically modified silica matrix alters the redox potential of the electroactive molecules. Electron exchange between the adjacent redox centers (electron hopping) is proposed as a possible charge propagation pathway through the insulating silica matrix, which is supported by the fact that the high charge uptake is observed also for the hybrid electrodes with the covalently anchored redox guests. 相似文献
95.
Justes DR Mitrić R Moore NA Bonacić-Koutecký V Castleman AW 《Journal of the American Chemical Society》2003,125(20):6289-6299
We present joint theoretical and experimental results which provide evidence for the selectivity of V(x)O(y)(+) clusters in reactions toward ethylene due to the charge and different oxidation states of vanadium for different cluster sizes. Density functional calculations were performed on the reactions between V(x)O(y)(+) and ethylene, allowing us to identify the structure-reactivity relationship and to corroborate the experimental results obtained by Castleman and co-workers (Zemski, K. A.; Justes, D. R.; Castleman, A. W., Jr. J. Phys. Chem. A 2001, 105, 10237). The lowest-energy structures for the V(2)O(2)(-)(6)(+) and V(4)O(8)(-)(10)(+) clusters and the V(2)O(3)(-)(6)(+)-C(2)H(4) and V(4)O(10)(+)-C(2)H(4) complexes, as well as the energetics for reactions between ethylene and V(2)O(4)(-)(6)(+) and V(4)O(10)(+) are presented here. The oxygen transfer reaction pathway was determined to be the most energetically favorable one available to V(2)O(5)(+) and V(4)O(10)(+) via a radical-cation mechanism.The association and replacement reaction pathways were found to be the optimal channels for V(2)O(4)(+) and V(2)O(6)(+), respectively. These results are in agreement with the experimental results reported previously. Experiments were also conducted for the reactions between V(2)O(5)(+) and ethylene to include an energetic analysis at increasing pressures. It was found that the addition of energy depleted the production of V(2)O(4)(+), confirming that a more involved reaction rather than a collisional process is responsible for the observed phenomenon. In this contribution we show that investigation of reactions involving gas-phase cationic vanadium oxide clusters with small hydrocarbons is suitable for the identification of reactive centers responsible for selectivity in heterogeneous catalysis. 相似文献
96.
The influence of mobile phase composition (acetonitrile-water ratio) on the separation of derivatised linear alkyl polyethoxylates (LAEs) is evaluated using thermodynamic quantities (Gibbs energy, enthalpy and entropy). In comparison to homologue series of alcohols oligomers of LAEs show irregular chromatographic behaviour that is demonstrated in irregular changes of thermodynamic quantities. It might be explained considering an influence of some of the following processes or their combinations on the retention of LAEs. These processes are solvation of oxyethylene chains in mobile phase, their interaction with silanols on silica surface of stationary phase and possibly their conformation changes. The composition of a mobile phase affects the mentioned processes and that is why the retention of LAEs is strongly (for the reversed-phase system unusually) sensitive to this composition in the studied range (volume fraction of acetonitrile phi = 0.90, 0.96 and 0.98). The experimental data also support the idea of the active role of stationary phase in the reversed-phase system. 相似文献
97.
Kotek J Lubal P Hermann P Císarová I Lukes I Godula T Svobodová I Táborský P Havel J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(1):233-248
In an aqueous solution at room temperature, 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (H(4)L(1)) and Cu(I) (I) form a pentacoordinated (pc) complex, pc-[Cu(L(1))](2-), exhibiting conformation I of the cyclam ring. At high temperature, the complex isomerises to a hexacoordinated isomer, trans-O,O-[Cu(L(1))](2-), with a trans-III conformation of the cyclam ring. In pc-[Cu(L(1))](2-), four ring nitrogen atoms and one phosphonate oxygen atom are arranged around Cu(I) (I) in a structure that is half-way between a trigonal bipyramid and a tetragonal pyramid, with one phosphonic acid group uncoordinated. In the trans-O,O-[Cu(L(1))](2-) isomer, the nitrogen atoms form a plane and the phosphonic acid groups are in a mutually trans configuration. A structurally very similar ligand, 4-methyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (H(4)L(2)), forms an analogous pentacoordinated complex, pc-[Cu(L(2))](2-), at room temperature. However, the complex does not isomerise to the octahedral complex analogous to trans-O,O-[Cu(L(1))](2-). Because of the high thermodynamic stability of pc-[Cu(L(1))](2-), (logbeta=25.40(4), 25 degrees C, I=0.1 mol dm(-3) KNO(3)) and the formation of protonated species, Cu(I) (I) is fully complexed in acidic solution (-log [H(+)] approximately 3). Acid-assisted decomplexation of both of the isomers of [Cu(H(2)L(1))] takes place only after protonation of both uncoordinated oxygen atoms of each phosphonate moiety and at least one nitrogen atom of the cycle. The exceptional kinetic inertness of both isomers is illustrated by their half-lives tau(1/2)=19.7 min for pc-[Cu(H(2)L(1))] and tau(1/2) about seven months for trans-O,O-[Cu(H(2)L(1))] for decomplexation in 5 M HClO(4) at 25 degrees C. The mechanism of formation of pc-[Cu(L(1))](2-) is similar to those observed for other macrocyclic complexes. 相似文献
98.
99.
The paper brings a preliminary submicro-level analysis of the temperature increase and acoustice mission caused by rnicrocrack propagation. The analysis is based on molecular dynamic simulations. 相似文献
100.