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91.
Aquation of [Cr(pic)3]0 and [Cr(pic)2(OH)]2
0 in aqueous HClO4 solutions leads to formation of the common product – [Cr(pic)2(H2O)2]+. The first, reversible stage, the ring opening via Cr—N bond breaking in [Cr(pic)3]0 is followed by the second, rate-determining step – one-end bonded pic ligand liberation. In the case of the [Cr(pic)2(OH)]2
0 complex, the first faster stage produces the singly bridged dimer, which undergoes cleavage into the parent monomers in the second, much slower step. The subsequent aquation of [Cr(pic)2(H2O)2]+ is extremely slow and leads to [Cr(pic)(H2O)4]2+ formation, which practically does not undergo further ligand substitution under the conditions applied. Kinetics of the first aquation stage for [Cr(pic)3]0 and of the second step for [Cr(pic)2(OH)]2
0 were studied spectrophotometrically in the 0.1–1.0 M HClO4 range at I = 1.0 M. The observed pseudo-first order rate constant for [Cr(pic)3]0 decreases with [H+] increase according to the rate law: k
obs = k
1 + k
–1
Q
1/[H+], where k
1 and k
–1 are the rate constants of the forward and the reverse processes in the unprotonated substrate and Q
1 is the protonation constant of the pyridine nitrogen atom. In the case of the [Cr(pic)2(OH)]2
0 complex, the rate for the singly bridged dimer cleavage does not depend on [H+]. The activation parameters for the chelate-ring opening in [Cr(pic)3]0 and for the singly bridged dimer cleavage have been determined and discussed. Some kinetic data of the slow, second aquation stage for the [Cr(pic)3]0 complex and of the fast, first aquation stage for the doubly bridged dimer have been studied; for both reactions the rate increases linearly with the increase in [H+]. 相似文献
92.
J. Szonert B. Bieniak M. Głódź M. Piechota 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,33(3):177-180
We report measurements of lifetimes of the Rb(n
2
F)(n=6, 7, 8) states performed in a vapour cell. TheF-states were excited in a two-step sequence of an electric-dipole transition followed by an electric-quadrupole transition. Single photon counting was used for detection. The results are: (62
F)=171(4), (72
F)=262(15), (82
F)=387(12) (in ns). These lifetimes, have been compared with theoretical values given by different authors. An estimate of the cross sections for quenching due to collisions with ground-state Rb atoms is also given.This work was supported by the Polish Committee for Scientific Research under grant No. 2 2341 92 03 相似文献
93.
T. A. Przylibski B. Kozłowska J. Dorda B. Kiełczawa 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(1):11-19
This work characterizes the occurrence of radionuclides 222Rn and 226Ra in the mineralized groundwaters of Gorzanów. The village is situated in the Sudeten Mountains, which are known in Poland for having increased concentrations of the aforesaid radionuclides in their groundwaters. However, in Gorzanów, the measured concentrations of 226Ra were low both in the reservoir rocks and mineralized waters. Consequently, the 222Rn concentration in the groundwaters also turned out to be low. The 226Ra content of these waters should mainly be associated with the dissolution of this nuclide, together with other main ions, at large depths, at slightly enhanced temperature. Radon-222, on the other hand, penetrates into the water during its outflow to the surface, in the zones of intensive friable deformations near fault zones. Thus, in the groundwaters of Gorzanów, the concentrations of these nuclides, subsequent in the uranium series, do not have a common genesis and they are not correlated with each other. 相似文献
94.
95.
On reaction with organolithium reagents followed by hydrolysis and distillation, N-vinylpyrrolidone ( 1 ) gives five-membered ring imines 3-8 , whereas N-vinylcaprolactam ( 2 ) gives mixtures of seven-membered ring imines and the corresponding ∈-amino ketones. 相似文献
96.
Micha Kijak Anna Zieli ska Charles Chamchoumis Jerzy Herbich Randolph P. Thummel Jacek Waluk 《Chemical physics letters》2004,400(4-6):279-285
Depending on the polarity and protic abilities of the solvent, 2-(2′-pyridyl)pyrrole can exist in either syn or anti rotameric forms. In nonpolar solvents, intramolecular excited state single proton transfer is observed, manifested by the appearance of low-energy tautomeric emission. The solvent-assisted excited state double proton transfer reaction is also detected. DFT calculations confirm low barriers for both single and double proton transfer processes in the lowest excited singlet state and show different character of the tautomerization in both cases: in the intramolecular reaction, mutual approach of two nitrogen atoms plays an important role. 相似文献
97.
Kzysztof Schmidt-Szałowski Anna Borucka Sławomir Jodzis 《Plasma Chemistry and Plasma Processing》1990,10(3):443-450
The catalytic action of granular silica packing on ozone formation has been observed under discharge conditions. Using a glass ozonizer with a metal high-voltage electrode, at a frequency of 400 Hz it was possible to obtain much higher ozone concentrations in the presence q( silica than without packing, with the same total energy consumption. The dependence between ozone production and energy efficiency is considered, and conditions of the optimum ozonizer run are discussed. It is shown that in the all-glass ozonizer with a narrow discharge gap, the ozone concentration may be as high as 6.5% (ca. 130g O3/m3) when silica packing is applied. 相似文献
98.
The asymmetric direct aldol condensation of aldehydes with ethyl- and propylketones is catalyzed by syn-alpha-aminoalcohol-Yb(OTf)3 complexes, yielding the anti-1,3-diol monoesters with high diastereocontrol and good enantioselectivity. Three adjacent stereogenic centers are created in a simultaneous aldol condensation and Evans-Tishchenko reduction in an acyclic system. 相似文献
99.
Andrzej Małecki Jalees A.K. Tareen Jean Pierre Doumerc Louis Rabardel Jean Claude Launay 《Journal of solid state chemistry》1985,56(1):49-57
Kinetics of thermal decomposition in vacuum of Co3O4 powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co3O4 proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)2/3 = ktn where the activation energy varies with the degree of decomposition. 相似文献
100.
Przychodzeń P Lewiński K Bałanda M Pełka R Rams M Wasiutyński T Guyard-Duhayon C Sieklucka B 《Inorganic chemistry》2004,43(9):2967-2974
The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer. 相似文献