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81.
André Deratani Thierry Maraldo Estelle Renard 《Journal of inclusion phenomena and macrocyclic chemistry》1995,23(2):137-146
Reduction of-cyclodextrin (-CD) aromatic ketone (acetophenone and acetonaphthones) inclusion compounds were carried out in the presence of a large number of chemically inert species as potential co-guests. In several cases, it was observed that stoichiometric molar ratios of these compounds to ketone significantly modify the chiral induction yielding the inverted alcohol enantiomer and increasing the face selectivity. The results were found to depend strongly on the respective structure and shape of both the ketone and the additive, and on the molar ratio of-CD:ketone:third compound. These observations suggest the formation of a three-component inclusion complex in which the geometry of binding of the substrate and its mobility are changed with respect to the binary system. 相似文献
82.
83.
84.
The crystal structure of a new complex Ti-Cr oxide phase, K0.82Mg1.68(Cr2.84Fe0.84Ti2.11Zr0.08)O12, synthesized at 13 GPa and 1400 °C, has been determined with single-crystal X-ray diffraction. It has a hexagonal symmetry with the space group P63/m and unit-cell parameters a=9.1763(13) and , , Z=1. The structure is characterized by the hollandite-type double chains of edge-shared M2 octahedra occupied by trivalent and tetravalent cations (Ti+Cr+Fe+Zr); these double chains are linked to one another through shared octahedral apexes to form a framework structure containing two types of tunnels running parallel to the c-axis. One type of tunnels has a hexagonal cross-section and is occupied by large K+, whereas the other has a triangular cross-section and is occupied by Mg2+. The K+ cation is disordered between two crystallographically equivalent (2a) sites in the tunnels and displays a U33 displacement parameter that is significantly greater than U11. The new high-pressure phase reported in this study possesses many structural features similar to those for the hollandite compounds, making it a candidate for the 1-D fast ionic conductors. 相似文献
85.
86.
The structures of the inclusion compounds formed by the host 9,9’-(ethyne-1,2-diyl)bis(fluoren-9-01) with pyridine and picolines are similar and display tubular topology. The host discriminates poorly between
these guests. The kinetics of desorption of the pyridine compound is governed by the Avrami-Erofe’ev equation A2, with an
activation energy of 111(7) kJ mol−1. 相似文献
87.
88.
Repeated temperature scanning method was applied to observe non-stoichiometry of YBa2Cu3O7-d, and interesting results were obtained. Two simultaneously occurring processes were separately observed in mass change;
one is a fast process and the other is slow, so that their responses to the temperature change are quite different from each
other. The fast process follows the cyclic temperature change, but the slow process is observed to be a gradual mass change.
Kinetic behaviors of these two processes are also made clear by plotting the mass vs. the temperature. Furthermore, a hysteresis
loop was observed in the plot of the mass vs. the temperature in a high temperature range presumably due to the third process,
and it depends on the heating and cooling rates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
89.
90.
Numerical results for the ground state of the HN
2
+
and HCO+ molecular ions at their near equilibrium geometry, obtained by the complex molecular orbitals (CMO) method in the extended basis set, are reported. The CMO wavefunction of the HN
2
+
ion is compared with the CI wavefunction obtained in the same basis set. This reveals the nature of approximations inherent in the CMO method. A peculiar feature of the occupation numbers of the CMO natural orbitals is also explained.Alexander von Humboldt Fellow. On leave from the Institute Rudjer Bokovi, Zagreb, Croatia, Yugoslavia. 相似文献