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2.
P. Rozier J. GalyG. Chelkowska H.-J. KooM.-H. Whangbo 《Journal of solid state chemistry》2002,166(2):382-388
The electronic and physical properties of Cu2.33V4O11 were characterized by electrical resistivity, magnetic susceptibility and X-ray photoelectron spectroscopy (XPS) measurements and by tight-binding electronic band structure calculations. Attempts to prepare Cu2.33−xV4O11 outside its narrow homogeneity range led to a mixture of Cu2.33V4O11, CuVO3 and β-CuxV2O5. The magnetic susceptibility data show no evidence for a magnetic/structural transition around 300 K. The XPS spectra of Cu2.33V4O11 reveal the presence of mixed valence in both Cu and V. The [Cu+]/[Cu2+] ratio is estimated to be 1.11 from the Cu 2p3/2 peak areas, so [V4+]/[V5+]=0.56 by the charge balance. Our electronic structure calculations suggest that the oxidation state of the Cu ions is +2 in the channels of CuO4 tetrahedra, and +1 in the channels of linear CuO2 and trigonal planar CuO3 units. This predicts that [Cu+]/[Cu2+]=1.33 and [V4+]/[V5+]=0.50, in good agreement with those deduced from the XPS study. 相似文献
3.
MO calculations predict a P-C rotation barrier in triformylphosphine of less than 6 kcal/mol, and an inversion barrier of ca 14 kcal/mol. 相似文献
4.
Yu-Ping Zhang Kwang-Pill Lee Hyun-Joo Noh Ali Md Showkat Seong-Ho Choi 《Microchemical Journal》2004,78(2):99-106
An appropriate optimization strategy should be used to find a desired resolution or selectivity with a minimum number of experiments in a limited time, which could assure the baseline separation of all target compounds. It was usually realized by means of a specialized computer program. In this paper, mapping optimization method and overlapping resolution mapping were compared for the optimization of a reversed-phase high-performance liquid chromatography (HPLC) isocratic separation of neutral compounds. The calculated resolutions and separation time of 7 to 10 experiments are fitted by different equations, which were used to build a contour plot with a minimum effective resolution and maximum retention time as a function of a mobile phase composition. The balance between resolution and analysis time could be easily realized by the overlapping of the final overlapping resolution mapping and analysis time mapping. The validity of the two methods was confirmed by some typical experiments. The models are simple, visual, and common without theoretical arithmetic. 相似文献
5.
First principles electronic structure calculations were carried out to determine the relative stabilities of the rutile- and CdI2-type structures of platinum dioxide (PtO2) and titanium dioxide (TiO2). The orbital interactions between the transition metal d- and oxygen p-orbitals were analyzed to gain insight into why PtO2 has both the rutile- and CdI2-type structures, but TiO2 has only the rutile-type structure. The cause for the large difference in the c/a ratios of the CdI2-type structures of TiO2 and PtO2 was examined. 相似文献
6.
The magnetic properties of Cu(2)(dca)(4)(2,5-me(2)pyz) have been reexamined. The extended structure of Cu(2)(dca)(4)(2,5-me(2)pyz) can be viewed in terms of Cu(2)(2,5-me(2)pyz)(4+) dimer units interconnected via mu(1,5)-dca ligands. The bulk magnetic susceptibility chi(T) and the isothermal M(H) of Cu(2)(dca)(4)(2,5-me(2)pyz) are shown to be well described by an isolated dimer model. This finding was confirmed by carrying out a spin dimer analysis based on tight-binding calculations, which shows that the 2,5-me(2)pyz ligand provides a substantial spin exchange interaction between the Cu(2+) ions while the dca ligands do not. 相似文献
7.
Second-order rate constants have been measured spectrophotometrically for the reactions of O-2,4-dinitrophenyl thionobenzoate (1) and 2,4-dinitrophenyl benzoate (2) with a series of substituted pyridines in 80 mol % H(2)O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. The Br?nsted-type plots obtained are nonlinear with beta(1) = 0.26, beta(2) = 1.07, and pK(a) degrees = 7.5 for the reactions of 1 and beta(1) = 0.40, beta(2) = 0.90, and pK(a) degrees = 9.5 for the reactions of 2, suggesting that the pyridinolyses of 1 and 2 proceed through a zwiterionic tetrahedral intermediate T(+/-) with a change in the rate-determining step at pK(a) degrees = 7.5 and 9.5, respectively. The thiono ester 1 is more reactive than its oxygen analogue 2 except for the reaction with the strongest basic pyridine studied (pK(a) = 11.30). The k(1) value is larger for the reactions of 1 than for those of 2 in the low pK(a) region, but the difference in the k(1) value becomes negligible with increasing the basicity of pyridines. On the other hand, 1 exhibits slightly larger k(2)/k(-1) ratio than 2 in the low pK(a) region but the difference in the k(2)/k(-1) ratio becomes more significant with increasing the basicity of pyridines. Pyridines are more reactive than alicyclic secondary amines of similar basicity toward 2 in the pK(a) above ca. 7.2 but less reactive in the pK(a) below ca. 7.2. The k(1) value is slightly larger, but the k(2)/k(-1) ratio is much smaller for the reactions of 2 with pyridines than with isobasic secondary amines in the low pK(a) region, which is responsible for the fact that the weakly basic pyridines are less reactive than isobasic secondary amines. 相似文献
8.
The electrical transport and magnetic properties of BaVS3, made up of individual VS3 octahedral chains, were examined on the basis of first principles and tight-binding electronic structure calculations. The electrical conductivity of BaVS3 is nearly isotropic despite its one-dimensional structural feature, because of the orbital interactions associated with the short S···S contacts within each VS3 chain and between adjacent VS3 chains. The probable cause for the metal-insulator transition at ∼70 K was examined in terms of first principles electronic structure calculations, which indicate that the metallic and magnetic insulating states of BaVS3 are nearly the same in energy. This is consistent with the observation that the metal-insulator transition at ∼70 K is caused by electron localization. The observed magnetic properties of BaVS3 below ∼70 K are readily explained under the assumption that the symmetry-broken t2g-orbitals act as the magnetic orbitals in the magnetic insulating state of BaVS3. The probable cause for the latter was discussed. 相似文献
9.
In the (MM'O6)infinity chains of the transition-metal magnetic oxides Ca3MM'O6 the MO6 trigonal prisms alternate with the M'O6 octahedra by sharing their triangular faces. In the (Co(2O6)infinity chains of Ca3Co2O6 (M = M' = Co) the spins are coupled ferromagnetically, but in the (FeRhO6)infinity chains of Ca3FeRhO6 (M = Fe, M' = Rh) they are coupled antiferromagnetically. The origin of this difference was probed by carrying out spin-polarized density functional theory electronic band structure calculations for ordered spin states of Ca3Co2O6 and Ca3FeRhO6. The spin state of a (MM'O6)infinity chain determines the occurrence of direct metal-metal bonding between the adjacent trigonal prism and octahedral site transition-metal atoms. The extent of direct metal-metal bonding in the (Co2O6)infinity chains of Ca3Co2O6 is stronger in the intrachain ferromagnetic state than in the intrachain antiferromagnetic state, so that the intrachain ferromagnetic state becomes more stable than the intrachain antiferromagnetic state. Such a metal-metal-bonding-induced ferromagnetism is expected to occur in magnetic insulators and magnetic metals of transition-metal elements in which direct metal-metal bonding can be enhanced by ferromagnetic ordering. In the (FeRhO6)infinity chains of Ca3FeRhO6 the ferromagnetic coupling does not lead to a strong metal-metal bonding and the adjacent spins interact by the Fe-O...O-Fe super-superexchange, hence leading to an antiferromagnetic coupling. 相似文献
10.
Etourneau J Ammar A Villesuzanne A Villeneuve G Chevalier B Whangbo MH 《Inorganic chemistry》2003,42(14):4242-4244
Electrical resistivity, magnetic susceptibility, and electron paramagnetic resonance measurements were carried out for cubic hexaboride KB(6), which is one electron short of completely filling its conduction band. It is found that KB(6) is not metallic and has localized spins. KB(6) exhibits a highly unusual hysteresis in the magnetic susceptibility below 100 K, which suggests that it undergoes a slow relaxation process. 相似文献