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排序方式: 共有226条查询结果,搜索用时 15 毫秒
1.
Accelerated phase transformations and chemical reactions of metastable aluminas and kaolinite, doped with Cu2
+, Mn3
+/Mn2
+ and Fe3
+/Fe2
+ ions, are accompanied with accelerated decrease of surface area and pore volume values. The phenomena in metal ion doped
samples are explained by a catalytic mechanism, in terms of the Jahn-Teller effect.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
R. Murugesan P. Sami T. Jeyabalan A. Shunmugasundaram 《Journal of Chemical Sciences》1995,107(1):1-10
Bonding and redox properties of mono- and dititanium substituted 12-heteropolytungsto-phosphates and their complexes with
bivalent Mn, Co, Ni and Cu are studied by UV-Vis, ESR and cyclicvoltammetric techniques. The heteropoly blue analogue [TiIIITiIVW10PO40]8− is unstable and its presence in solution is proved by optical and ESR spectroscopy. ESR results reveal that the odd electron
is trapped on the titanium atom at 77 K. The optical electronegativity of Ti(III) in this heteropoly blue is estimated to
be 2.4 from the intervalence charge transfer (IVCT) bands. X-ray powder diffraction results show that the complexes K5MII[Ti2W10PO40].xH2O(MII = Cu or Mn) are isomorphous with K7[Ti2W10PO40].6H2O. Electronic spectroscopy indicates very high symmetry around the bivalent metal ion M in the K5MII[Ti2W10PO40].xH2O complexes. This high symmetry is confirmed in K5Cu[Ti2W10PO40] by the observation of dynamic Jahn-Teller (JT) distortion at 300 K and static JT distortion at 77 K. 相似文献
3.
T. V. Ramakrishnan H. R. Krishnamurthy S. R. Hassan G. Venketeswara Pai 《Journal of Chemical Sciences》2003,115(5-6):767-774
Manganites of the LA1−x
Ca
x
MnO3 family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach
recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee
g
states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment
of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and
CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and
spatial correlation is the key to manganite physics.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
4.
二(邻香草醛缩丙醇胺)异硫氰酸根合锰(Ⅲ)的合成与晶体结构 总被引:2,自引:0,他引:2
本文报道了一个新配合物—二(邻香草醛缩丙醇胺根)异硫氰酸根合锰(Ⅲ)的合成及其晶体结构。配合物属于单斜晶系,空间群为P21/c,晶胞参数为:a=8.565(1), b=21.814(2), c=12.787(2)?, β=92.80(1)°。锰为六配位,在两个邻香草醛缩丙醇胺Schiff碱配体中,一个为三齿配体,另一个为双齿配体。NCS-离子以N在轴向上与锰发生配位,由于Jahn-Teller效应,其键长为2.193?。另外晶胞中存在着罕见的H……S-C≡N氢键。 相似文献
5.
6.
J.B Goodenough J.-S Zhou F Rivadulla E Winkler 《Journal of solid state chemistry》2003,175(1):116-123
Bond-length fluctuations in transition-metal oxoperovskites may give rise to two-phase fluctuations in what appears to be a single phase to a diffraction experiment. Orbital disorder at Jahn-Teller ions results in bond-length fluctuations that give 3D-ferromagnetic, vibronic Mn(III)-O-Mn(III) superexchange interactions and allow disproportionation into Mn(IV) and Mn(II) in LaMnO3; where orbitally ordered and disordered phases coexist, an external magnetic field stabilizes the orbitally disordered, ferromagnetic phase relative to the orbitally ordered, antiferromagnetic phase. Spin-lattice interactions in the paramagnetic phase of charge-transfer compounds give bond-length fluctuations arising from the semicovalent component of the superexchange interactions. At the crossover from localized to itinerant electronic behavior, the coexistence of two-phase fluctuations has been demonstrated in both the single-valent RNiO3 family (R=rare-earth, A=alkaline-earth) and the mixed-valent R0.5A0.5MnO3 perovskites. “Bad-metal” behavior is found to be associated with bond-length fluctuations. 相似文献
7.
Isaac B. Bersuker Natalia N. Gorinchoi Victor Z. Polinger 《Theoretical chemistry accounts》1984,66(3-4):161-172
The vibronic origin of dynamic instability of molecular systems considered earlier, is here given a more complete and rigorous treatment. It is shown that the nonvibronic contribution to the curvature of the adiabatic potential arising due to nuclear displacements under fixed electronic density distribution, is always positive, and hence the only reason for dynamic instability is the pseudo Jahn-Teller effect. For some examples of special interest (planar equilateral NH3, planar square CH4 and linear H
3
+
) the molecular excited states, responsible for the instability of the ground state, are revealed by means of ab initio calculations. 相似文献
8.
d~9电子构型的金属离子所形成的配合物几何构型一般为拉长八面体或平面正方形,晶体场理论和角重叠模型都对此作出了较满意的描述,但就该电子构型的中心离子与指定配体配位时易形成配合物的配位数、配体所处的位置等问题,至今尚无满意解释.本文通过分子轨道稳定化能(MOSE)的计算及其曲面的绘制,形象地解释了上述问题. 相似文献
9.
合成了一个新配合物[Mn(napn)(CH3OH)2]ClO4 (C26H26 Cl N2O8Mn,Mr = 584.88,H2napn = 双a-萘酚醛缩乙二胺),并测定了其晶体结构。晶体属于三斜晶系,空间群P ,a = 7.813(1),b = 13.025(2),c = 14.089(2) ? = 64.89(3), = 83.98(3), = 78.11(3)海琕 = 1270.16 ?,Z = 2, Dc = 1.529 g/cm3, F(000) = 604, R = 0.0837, wR = 0.1636。锰(Ⅲ)离子的配位构型为拉长的八面体。Schiff碱配体napn2-中的N2O2在赤道平面与锰(Ⅲ)形成四配位,2个CH3OH中的O原子分别在赤道平面两侧轴向位置与锰(Ⅲ)配位。由于Jahn-Teller效应,轴向上的MnO平均键长为2.52 拧A硗猓О写嬖诜肿幽诤头肿蛹淝饧? 相似文献
10.
Inés Sánchez-Movellán Jorge Moreno-Ceballos Dr. Pablo García-Fernández Prof. Jose Antonio Aramburu Prof. Miguel Moreno 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(54):13582-13590
In the search for new high-temperature superconductors, it has been proposed that there are strong similarities between the fluoroargentate AgF2 and the cuprate La2CuO4. We explored the origin of the possible layered structure of AgF2 by studying its parent high-symmetry phase and comparing these results with those of a seemingly analogous cuprate, CuF2. Our findings first stress the large differences between CuF2 and AgF2. Indeed, the parent structure of AgF2 is found to be cubic, naturally devoid of any layering, even though Ag2+ ions occupy trigonal sites that, nevertheless, allow the existence of a Jahn-Teller effect. The observed Pbca orthorhombic phase is found when the system is cooperatively distorted by a local E⊗e trigonal Jahn-Teller effect around the silver sites that creates both geometrical and magnetic layering. While the distortion implies that two Ag2+−F− bonds increase their distance by 15 % and become softer, our simulations indicate that covalent bonding and interlayer electron hopping is strong, unlike the situation in cuprate superconductors, and that, in fact, exfoliation of individual planes might be a harder task than previously suggested. As a salient feature, these results prove that the actual magnetic structure in AgF2 is a direct consequence of vibronic contributions involved in the Jahn-Teller effect. Finally, our findings show that, due to the multiple minima intrinsic to the Jahn-Teller energy surface, the system is ferroelastic, a property that is strongly coupled to magnetism in this argentate. 相似文献