Electron Localization versus Delocalization and Ferromagnetic Coupling in Mixed Valence Polyoxometalates

We show that the ferromagnetism, recently found in the doubly-reduced hexanuclear polyoxometalate [V₆O₁₂ (μ₂−OCH₃)₄(L)₄] does not contradict to the proposed earlier delocalization mechanism of the stabilization of a spin- singlet state. The ground state triplet state yields from the internal and/or external complex asymmetry leading to the spin density localization.     

过渡金属偶氮苯衍生物二阶非线性光学性质的密度泛函理论研究

采用含时密度泛函理论方法(TDDFT)计算了IB族过渡金属及第5周期的金属杂化偶氮苯生色团的二阶非线性光学极化率。研究了金属杂化偶氮苯生色团的电子激发跃迁。结果表明, 与金属离子络合后的杂化偶氮苯生色团, 二阶非线性光学极化率明显改变, 是金属的推拉电子效应的结果。IB族金属的在原有机偶氮苯共轭体系的电荷转移方向的强拉电子效应, 增大了电荷转移范围, 使二阶非线性光学极化率增大。与Nb络合的杂化生色团, 沿原电荷转移相反的方向拉动电荷, 电荷转移跃迁局限于金属离子附近, 未能产生大的激发跃迁偶极矩, 体系的二阶非线性光学响应因而降低。激发跃迁能量是另一个主要影响因素, 同一类跃迁中, 金属杂化生色团的跃迁能量越低, 其二阶非线性光学响应就越大。络合Rh的生色团与Nb杂化生色团类似, 电荷转移跃迁范围都比较小, 同时由于Rh与羧基结合时几乎垂直羧基平面, 电荷同时沿X, Y方向转移跃迁, 属于二维电荷转移类型。     

Heisenberg-Dirac-van Vleck model applied to describing the magnetic parameters of mixed-valency clusters

A study has been made on using a Heisenberg-Dirac-van Vleck model in the magnetochemistry of class II mixed-valency cluster compounds. That model may be modified with allowance for electron transfer but cannot be applied to mixed-valency dimers when there is a high degree of excess-electron localization but with small values of the exchange integral. For large values of the exchange integral, that model leads to an incorrect value for the ground-state spin even for localized systems. The correct approach here is based on calculating the spin-vibronic energy spectrum.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 28, No. 2, pp. 121–124, March–April, 1992.     

三核欠完整立方烷金属原子簇二阶非线性光学性质的理论研究

研究了具有欠完整立方烷构型的过渡金属原子簇分子的二阶非线性光学性质。利用TDDFT方法计算了选取的簇分子及相应模拟构造分子的静态和动态的一阶非线性光学超级化率(ijk);并计算了不同金属、桥原子和配体以及簇芯对该类化合物一阶超级化率的影响。选取其中的一个簇分子为基本模型,分析了该分子的电子结构和分子轨道,在微观水平上阐述了其非线性光学性质的可能起源。认为由过渡金属和硫原子组成的簇芯和与桥原子相连的配体对该类簇合物的二阶非线性光学性质的起决定性的作用。     

Exchange coupling of paramagnetic ions in a polyoxometalate matrix: density functional study of diiron(III) substituted gamma-silicotungstates

The quantum chemical (density functional) analysis of the antiferromagnetic interactions between the two iron centers incorporated into the gamma-silicotungstate is performed. The influence of the polyoxometalate framework on the exchange coupling within the diiron core unit is studied. The dependence of the strength of antiferromagnetic exchange on the protonation of the core bridges is considered. It is shown that the magnetic coupling is very sensitive to the distortions in core geometry. Variations in the core structure induced by the environment (such as the polyoxometalate framework) change the significance of superexchange pathways and give rise to new superexchange mechanisms. This effect is especially pronounced in the case of the hydroxo-bridged diiron core.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.     

158 A Ge V p-Pb Pb-Pb碰撞中的单奇异和多奇异粒子产生

用描写相对论性核 核碰撞的LUCIAE模型及相应的MonteCarlo事例产生器分析了WA97最近发表的 1 5 8AGeVp Pb和Pb Pb碰撞中单奇异粒子 (Λ ,Λ)和多奇异粒子 (Ξ-,Ξ-,Ω-,Ω-)的多重数和横质量分布 .由于LUCIAE模型包含了弦碎裂微观过程中奇异夸克压低因子随碰撞体系的能量、中心度和质量的增大而增大 ,以及由它导致的相对论性核 核碰撞宏观过程中奇异粒子产额随上述三因素之增而增的物理机制 ;LUCIAE模型计算结果能较好描写WA97实验所揭示的相对论性核 核碰撞中奇异粒子产额随中心度之增而增和奇异粒子增强随奇异夸克数之增而增的实验事实 ,以及单奇异和多奇异粒子的横质量分布 .     

甘氨酸钙络合物的熔融法合成及表征

以甘氨酸和氢氧化钙为原料,采用熔融法合成了甘氨酸钙络合物,最佳合成条件为:原料摩尔比n甘氨酸:nCa(OH)2=2:1,在熔融状态下,反应温度150℃左右,反应时间40min,并通过元素分析、红外光谱、X-射线粉末衍射、差热-热重等实验手段对该络合物进行了表征,确定其化学式为Ca(NH2CH2COO)2,所得产品的产率达94.1%.     

DEPENDENCE OF PHASE TRANSITION ON THE MASS NUMBER OF HOT NUCLEI

The dependence of phase transition,associated with the disassembly of hot nuclei,on the mass number of hot nuclei is investigated.By studying six hot nuclei ranging from ⁵⁶Ni* to ²³⁸U*,we find that in the curves of excitation energy of hot nuclei vs.Thermodynamic temperature T(E*) of ⁶³Cu* and heavier ones there are always two temperature plateaus,but in T(E*) of ⁵⁶Ni the first temperature plateau (at lower excitation energy) shrinks into a kink.     

ON THE BEHAVIOR OF PHASE TRANSITION SHOWN IN DISASSYMBLY PROCESSES OF VERY HOT AND DILUTE FINITE NUCLEAR SYSTEMS

The behaviors of phase transition shown in disassymbly processes of very hot and dilute finite nuclear system have been exposed by using canonical (microcanonical) ensemble Monte Carlo simulation.It is explained that they result from the competition between Coulomb interaction and the effect of finiteness.