Magnetic Orbitals and Mechanisms of Exchange II. Superexchange

Summary. In a first step, we examine the concept of magnetic orbital which is very useful to treat the mechanism of superexchange. After that, we recall the general broad lines of the first historical model proposed by Anderson. In a second step, we develop a new general treatment for superexchange, in the case of the centrosymmetrical model AXB, where A and B are metal cations and X a common bridging ligand (with here, for simplification, A = B, without transfer between cations). It allows one to retrieve the expression of exchange energy J vs. key molecular integrals, as respectively proposed by several authors such as Anderson on the one hand, Hay, Thibeault, and Hoffmann on the other one, and, finally, Kahn and Briat. This model may be easily generalized to the case where a transfer does exist between both cations, with A = B or A ≠ B. An erratum to this article is available at .     

1-碘丙烷分子的电子动量谱学研究：自旋-轨道耦合效应与分子内轨道相互作用

利用不对称不共面电子动量谱仪,在2.5 keV碰撞能量下,采用高精度的SAC-CI方法计算了1-碘丙烷分子束缚能谱,同时采用Hartree-Fock、B3LYP/aug-cc-pVTZ（C,H）6-311G＊＊（I）方法计算其电子动量分布. 并对电离能峰进行了标示. 结合非相对论与相对论计算方法以及自然键轨道分析,对最外层两个轨道（碘的5p孤对）的自旋-轨道耦合效应与分子内轨道相互作用进行了比较. 两种相互作用对电子动量分布的不同影响是可观的. 实验结果与相对论计算的结果一致,表明1-碘丙烷分子内自旋-轨道耦合效应占主导.     

Localized Orbitals vs. Pseudopotential-Plane Waves Basis Sets: Performances and Accuracy for Molecular Magnetic Systems

 Density functional theory, in combination with a) a careful choice of the exchange-correlation part of the total energy and b) localized basis sets for the electronic orbitals, has become the method of choice for calculating the exchange-couplings in magnetic molecular complexes. Orbital expansion on plane waves can be seen as an alternative basis set especially suited to allow optimization of newly synthesized materials of unknown geometries. However, little is known on the predictive power of this scheme to yield quantitative values for exchange coupling constants J as small as a few hundredths of eV (50–300 cm⁻¹). We have used density functional theory and a plane waves basis set to calculate the exchange couplings J of three homodinuclear Cu-based molecular complexes with experimental values ranging from +40 cm⁻¹ to −300 cm⁻¹. The plane waves basis set proves as accurate as the localized basis set, thereby suggesting that this approach can be reliably employed to predict and rationalize the magnetic properties of molecular-based materials. Corresponding author. E-mail: Carlo.Massobrio@ipcms.u-strasbg.fr Received August 5, 2002; accepted August 9, 2002     

Investigation on Magnetic Properties of Exchange Coupled Transition Metal Complexes──I．ApplicationoftheKambe＇sTheory

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SmCo磁记录薄膜中磁耦合作用的研究

采用磁控溅射方法,在玻璃基片上制备了Cr/SmCo/Cr结构的SmCo薄膜,实验结果表明:在低Sm含量(20.5%(原子分数))和高Sm含量(大于30.7%)的SmCo薄膜中都能形成SmCO_5磁性相,在Sm含量较高的SmCo薄膜中同时还形成了SmCo_2等非磁性相,非磁性相的存在对磁性相有隔离作用,从而降低了磁性晶粒之间的磁耦合作用.因此可以用提高Sm含量的方法来降低SmCo薄膜磁性晶粒之间的磁耦合作用.     

十六烷基三甲基氯化铵与直接蓝199的相互作用

采用吸收光谱法和电导率法,研究了阳离子表面活性剂十六烷基三甲基氯化铵（CTAC）与直接蓝199(DB199)的相互作用。 实验结果表明,当CTAC的浓度低于临界胶束浓度（CMC）时,混合溶液的电导率随CTAC浓度变化曲线与理论计算曲线基本吻合;高于CMC时,CTAC溶液中有80.88%的Cl-吸附在胶束的表面,当加入染料之后数量会降至78.48%。 混合溶液的最大吸收波长（λmax）随着CTAC浓度的增加先发生蓝移后红移。λmax处吸光度随着CTAC的浓度增大先下降后上升。     

Investigation on Magnetic Properties of Exchange Coupled Transition Metal Complexes Ⅱ．Theoretical Model for Trinuclear Complexes

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Magnetic perturbation of the redox potentials of localized and delocalized mixed-valence complexes

The potential differences (ΔE) between the two one-electron events observed for symmetrical mixed-valence (MV) complexes is generally used as a measurement of the thermodynamic stability of the MV state and often extended to the evaluation of the strength of the coupling between the redox centers through the bridge. In this review article, selected examples illustrate how the ΔE values to assess the degree of electronic communication between metals must be approached very judiciously. The role of the magnetic exchange which can take place between the unpaired spins carried by the redox sites in the doubly oxidized complexes is emphasized.     

烯醇式异桥双铜配合物的合成及磁交换作用的研究

合成了２个异桥双铜配合物：［Ｃｕ２（ｐｆｈｍｐ）Ｂｒ］·２Ｈ２Ｏ（１）和［Ｃｕ２（ｐｆｈｍｐ）Ｃ３Ｈ３Ｎ２］·２Ｈ２Ｏ（２），经元素分析、红外及摩尔电导等手段推知两配合物均为烯醇式构型。变温磁化率测定结果表明，由于外源桥的影响，铜离子间的反铁磁相互作用有明显差别。     

新型酮式,烯醇式双铜配合物的合成及磁交换作用研究

合成和表征了2个双核铜配合物——酮式-[CU_2(H_2L)Cl]Cl_2和烯醇式-[Cu_2(L)Cl]·H_2O,推知2个配合物分别为酮式和烯醇式,烯醇式配合物中铜离子间的反铁磁相互作用(J=-461.80cm~(-1))大于酮式配合物中的相应值(J=-33.16cm~(-1))。     

球形纤维素磁性阴离子交换树脂的化学转化制备及特性研究

自制了大孔球形纤维素基阴离子交换树脂(PSC-AN),并利用化学转化法成功制备了大孔球形纤维素基磁性阴离子交换树脂(PSC-MAN)。对影响树脂质量磁化率的几个主要因素进行了探讨,实验确定最佳制备条件为:铁盐的配比为1∶10,EDTA的浓度为0.005 mol/L。对树脂的结构和性能进行了研究,表明化学转化法制备大孔球形纤维素基阴离子交换树脂(PSC-MAN)磁性强,在碱液中相当稳定,树脂磁化前后交换容量分别为Q前=1.33 meq/g、Q后=1.16 meq/g,即树脂基的交换容量基本不受磁化过程的影响。     

氟尿嘧啶与磁性层状复合氢氧化物的离子交换反应动力学

以共沉淀法合成的磁性层状复合氢氧化物(Magnetic layered double hydroxide, MLDH)为前驱体, 通过对原位反应系统液相数据的拟合与固相样品的表征, 研究了0~50 ℃条件下MLDH与氟尿嘧啶(5-FU)的离子交换动力学特征. 结果表明, MLDH及离子交换产物MLDH-FU为以六方晶系为主并混杂微量氧化铁的复合磁性晶相; MLDH-FU离子交换速率随温度的升高而显著加快, FU, OH^-和Cl^- 3种客体的浓度变化分别服从二级、 零级及一级反应速率模型, 反应活化能依次为12.69, 27.88和3.580 kJ/mol. 固相表征参数的变化与液相动力学过程、 主-客体结构调整及MLDH-FU粒子陈化过程相符; 离子交换限定在LDH层间, 不涉及层板内部秩序, 不改变前驱体的结构与形貌特征, 具有侧向非断层反应习性, 是交换剂在MLDH外周经吸附亲和、 侧向进攻、 层间置换及柱撑模型转换再到新的插层客体主导调整及晶粒发育陈化的有序过程.     

Magnetic properties of d–d–d MV trimers with partial electron delocalization in the generalized vibronic model

The effects of magnetic exchange, double exchange and vibronic coupling on magnetic properties of the d¹–d¹–d² trimer with C_2V symmetry are discussed in the generalized vibronic model. The magnetic moments are calculated with the semiclassical adiabatic approach. The results show that the PKS vibronic coupling and the P vibronic coupling favor the localization and the delocalization of the ‘extra’ electron, respectively. The magnetic properties are determined by the interplay among magnetic exchange, double exchange and vibronic coupling.     

Magnetic susceptibilities of acetylene and ethylene using frost-model wavefunctions withp-type Gaussians

There are degeneracy problems involved in the calculation of magnetic susceptibilities from Frost model wavefunctions built up from mixeds- andp-type Gaussians. Various methods are suggested to alleviate the difficulties and they are used to compute the susceptibilities of C₂H₂ and C₂H₄.     

新型异桥烯醇式双铜配合物的合成及磁交换作用的研究

合成了2个含不同外源桥基的双铜配合物[Cu_2(pfhmp)OH]·2H_2O和[Cu_2(pfhmp)N_3]·H_2O,pfhmp~(3-)表明N,N′-二异烟酰基-2-羧基-4-甲基-1,3-苯二甲醛双腙的脱氢阴离子。经元素分析、红外光谱、摩尔电导等手段推知两配合物均为异桥结构与烯醇式构型,变温磁化率测定表明改变外源桥基会明显改变2个铜离子之间的磁交换作用。     

Polysaccharides of Fabaceae. I. Galactomannan of Astragalus sericeocanus seeds

Galactomannan (yield 3.58% of seed mass) of molecular weight 876 kDa was isolated from seeds of Astragalus sericeocanus Gontsch. (Fabaceae). Its solutions had high viscosity [η], 764.6 mL/g, and optical density [α]_D +65.3°. The polysaccharide consisted of galactose and mannose in molar ratio 1:1.58. The main chain of the galactomannan macromolecule was constructed of 1,4-β-D-mannopyranose units, 63% of which were substituted at C-6 by single α-D-galactopyranose units. ¹³C NMR spectroscopy established that the galactomannan contained units of differently substituted galactose mannobiose units: Man-Man, (Gal)Man-Man, and/or Man-Man(Gal) in addition to (Gal)Man-Man(Gal), the ratio of which was 0.15:0.51:0.34. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 555–557, November–December, 2008.     

Thermodynamics of the isopropanol/n-hexane and isopropanol/n-heptane systems. Part I. Infrared studies

The association equilibria for different conglomerates are calculated for the isopropanol/n-Hexane, isopropanol/n-Heptane systems from the infrared spectra.

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Zur Thermodynamik des Isopropanol/n-Hexan und Isopropanol/n-Heptan Systems, I. Untersuchungen mittels IR-Spektroskopie

Zusammenfassung Es werden die Assoziationsgleichgewichte für verschiedene Konglomerate im Isopropanol/n-Hexan- bzw.-/n-Heptan-System aus den IR-Spektren abgeleitet.

     

Small-angle X-ray scattering studies on the X-ray induced aggregation of malate synthase I. Structural and kinetic studies

Small-angle X-ray scattering measurements on malate synthase in aqueous solution revealed a continuous increase of the intensity in the innermost portion of the scattering curve with increasing measuring time. We have definite evidence that this increase reflects an X-ray induced aggregation of the enzyme particles in the course of the small-angle X-ray scattering experiment. Obviously this aggregation is a consequence of a radiation damage of the particles by the primary beam used in the scattering experiment.The aggregation process of malate synthase was monitoredin situ by smallangle X-ray scattering. For this purpose scattering curves were taken at various stages of aggregation. The analysis of these curves established the increase of the particle dimensions, the retention of the pseudo thickness factor of the native enzyme and the occurrence of one and later on of two pseudo cross-section factors. These results suggest the way how the aggregation might proceed. The results led to a tentative model of the aggregation process in which a one-dimensional side-by-side association of the oblate enzyme particles is followed by a two-dimensional aggregation. An aggregation in the third dimension was not observed during the time covered by our experiment.The time dependence of molecular parameters, for instance of the apparent mean radius of gyration, was used to compare the aggregation of enzyme samples that were irradiated under different experimental conditions. The addition of dithiothreitol to the enzyme solutions as well as the presence of the substrates or of a substrate analogue or of ethanol were found to reduce the rate of aggregation.

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Röntgenkleinwinkeluntersuchungen der durch Röntgenstrahlen induzierten Aggregation der Malatsynthase. I. Strukturuntersuchungen und kinetische Messungen

Zusammenfassung Röntgenkleinwinkeluntersuchungen an wäßrigen Lösungen von Malatsynthase zeigten eine mit der Meßdauer ansteigende Zunahme der Streuintensität im Innenteil der Streukurve. Dieser Intensitätsanstieg spiegelt zweifelsohne eine durch die Röntgenbestrahlung induzierte Aggregation der Enzymteilchen während der Röntgenkleinwinkelmessung wider. Diese Aggregation ist offensichtlich auf einen durch die Primärstrahlung verursachten Strahlenschaden zurückzuführen.Das Fortschreiten der Aggregation der Malatsynthase wurde mit Hilfe der Röntgenkleinwinkelstreuungin situ verfolgt. Zu diesem Zweck wurden Streukurven bei verschiedenen Aggregationsstadien aufgenommen. Die Analyse dieser Kurven zeigte die Zunahme der Teilchendimensionen, das Beibehalten des Pseudodickenfaktors des nativen Enzyms und das Auftreten eines und später zweier Pseudoquerschnittsfaktoren an. Diese Ergebnisse lieferten Hinweise, wie die Aggregation ablaufen könnte, und führten zu einem möglichen Modell für den Aggregationsvorgang. Demnach sollte auf eine eindimensionale, laterale Aggregation der oblaten Enzymteilchen eine zweidimensionale Aggregation folgen. Ein Fortschreiten der Aggregation in der dritten Dimension konnte während der Dauer des Experimentes nicht beobachtet werden.Die zeitliche Abhängigkeit molekularer Parameter, z. B. des apparenten mittleren Streumassenradius, wurde für den Vergleich der Aggregation von Enzymproben, die unter verschiedenen experimentellen Bedingungen bestrahlt wurden, herangezogen. Durch Zugabe von Dithiothreitol oder Ethanol zu den Enzymlösungen oder durch die Anwesenheit der Substrate oder eines Substratanalogen konnte die Aggregationsgeschwindigkeit herabgesetzt werden.