Stretching vibrations and structure of (HF) n (n=4–8) clusters

IR spectra of 24 structural isomers of (HF) _n (n=4–8) clusters were calculated in the framework of semiempirical theory of polyatomic molecule vibrations. Based on the results obtained and available experimental data it is proposed that (HF) _n associates comprising 3–5-membered cycles with attached monomeric HF units are present in molecular beams and gas phase.Ab initio calculations performed by the SCF method show the existence of local minima corresponding to such structures on the potential energy surface of (HF) _n clusters (n=4–6). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 435–443, March, 1997.     

零维到三维结构中三核铜自旋阻挫簇单元的磁构关系和反对称交换

量子自旋液体是最近几年刚被人们证实除铁磁体、反铁磁体之外的第三种磁性类型,因其有望解释高温超导的运行机制、改变计算机硬盘信息存储方式而在物理、材料等领域备受关注。自旋阻挫作为量子自旋液体的最小单元可能是解开量子自旋液体诸多问题的钥匙,所以在磁学、电学研究领域再一次成为人们研究的热点。基于文献报道的三核铜配合物[Cu3(μ3-OH)(μ-OPz)3(NO3)2(H2O)2]·CH3OH(1),我们合成了三维金属有机框架配合物{[Ag(HOPz)Cu3(μ3-OH)(NO3)3(OPz)2Ag(NO3)]·6H2O}n(2)(HOPz=甲基(2-吡嗪基)酮肟),并从自旋阻挫的角度对二者磁性质进行对比和详细分析。磁化率数据表明自旋间有很强的反铁磁相互作用和反对称交换。通过包含各向同性和反对称交换的哈密顿算符对两者磁学数据进行拟合并研究其磁构关系,所获最佳拟合参数为:配合物1:Jav=-426 cm^-1,g⊥=1.83,g∥=2.00;配合物2:Jav=-401 cm^-1,g⊥=1.85,g∥=2.00。     

Water-Soluble Organometallic Compounds. 8[1]. Synthesis, Spectral Properties, and Crystal Structures of 1,3,5-Triaza-7-phosphaadamantane (PTA) Derivatives of Metal Carbonyl Clusters: Ru3(CO)9(PTA)3 and Ir4(CO)7(PTA)5

The syntheses of Ru₃(CO)₉(PTA)₃ and Ir₄(CO)₇(PTA)₅ were accomplished through the thermal reactions of Ru₃(CO)₁₂ or Ir₄(CO)₁₂ with the water-soluble phosphine, PTA(1,3,5-triaza-7-phosphaadamantane). The ruthenium derivative was shown by X-ray crystallography to consist of a triangular Ru₃ core with three nearly equal Ru–Ru bonds, with each ruthenium atom bearing an equatorially positioned PTA ligand. In Ir₄(CO)₇(PTA)₅ the iridium atoms define a tetrahedron which is bridged on three edges by CO ligands. One basal iridium atom contains two PTA ligands, while the other two basal and the apical iridium atoms each possess one PTA ligand in their coordination spheres. Although, Ru₃(CO)₉(PTA)₃ is only sparingly soluble in pure water, it is very soluble in aqueous solution of pH<4. Indeed the triruthenium cluster can be extracted reversibly between an aqueous and an organic phase (e.g., CH₂Cl₂) by changing the pH of the aqueous phase. On the other hand the more highly PTA substituted cluster, Ir₄(CO)₇(PTA)₅, exhibits good solubility in aqueous solution (pH 7 and below) and a variety of organic solvents. Both cluster derivatives are stable in deoxygenated, aqueous solutions for extended period of time (>24 h).     

19F-NMR-spektroskopischer Nachweis und Berechnung der statistischen Bildung der gemischten Clusteranionen [(Mo6BrCl)F]2−, n = 0 – 8

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆Br Cl )F ]^2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo₆BrCl)⁴⁺ is formed by exchange of innersphere bound Clⁱ against outersphere bound Br^a on tempering the solid [(Mo₆Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H₃O)₂[(Mo₆BrCl)Cl] and precipitation of the outer Cl^a with AgBF₄ in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)₂ [(Mo₆BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 ¹⁹F nmr signals are expected, which are really observed in the high resolution 1D-¹⁹F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-¹⁹F/¹⁹F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers.     

Laser vaporization: A versatile method for studying metal clusters

Vaporizing solid samples of metals and semiconductors with a YAG Laser is a method well suited for producing molecules and clusters of those materials. The clusters are examined by either laser-induced fluorescence (LIF) or mass spectroscopic methods. The technique is valuable for both gas phase and matrix studies. The method is described and some applications, studying either the structure of small metal molecules or their reactions, are reviewed, with emphasis on our recent results from the LIF studies of LiBe, Al₂ and the reaction of Al with oxygen, yielding A1₂O. For larger clusters, Ion Cyclotron Resonance is an extremely valuable method, as we demonstrate by its application to the reactions of small charged silicon clusters with strong oxidising agents.     

Preparation and reactivity of metal-containing monomers

Mono- and disubstituted cluster metal-containing monomers were obtained under mild conditions on interaction of Rh₆(CO)₁₆ with 4-vinylpyridine (4-ViPy) in the presence of N-trimethylaminoxide. These products were characterized by IR and¹H NMR spectroscopy and by elemental and X-ray analyses. Rh₆(CO)₁₅(4-ViPy) was found to be an octahedral cluster with eleven terminal and four ₃-bridging carbonyl ligands. 4-ViPy is linked with the Rh(3) atom through the N atom and occupies the coordination site of the twelfth CO terminal ligand. The mean value of the Rh-Rh bond length is 2.762 Å. The unsaturated ligand has little or no effect on the geometry of the starting cluster and its double bond retains the ability to undergo addition reactions.For part 28, seeRuss. Chem. Bull., 1993, 453.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 975–979, May, 1993.     

Anab initio investigation of Cu2Se and Cu4Se2

Summary Experimentally known copper selenium clusters show extraordinary geometrical features, especially short Cu-Cu distances. We report the first theoretical investigation of Cu₂Se and Cu₄Se₂. Various quantum chemical methods (SCF, MP2, CPF, CCSD, CCSD(T), LDF) are applied to determine the importance of dynamic electron correlation. We find that inclusion of correlation does not essentially change the electronic structure of the clusters but has a strong influence on geometries. To reduce the computational effort we apply effective core potentials (ECPs) in combination with small, but carefully optimized basis sets. The applicability of simple modellings of correlation energies for approximate inclusion of correlation effects in SCF geometry optimizations is tested.     

铅硫二元团簇Pb5S+4的理论研究

用密度泛函方法对铅硫二元团簇Ｐb５Ｓ４＋的结构和性能进行了理论研究。结果表明,具 有Ｃ,对称性的笼状结构的异构体最稳定。根据计算所推测的该团簇的性质与实验结果下一致。     

碳原子簇的结构与质谱的关联（Ⅱ）

根据出现在质谱中的各种大小的碳原子簇的相对丰度,分析了由激光产生的碳原子簇离子的统计分布,研究了这些统计分布与碳原子簇结构的关联。研究结果表明：相同构型的原子簇的相对丰度可以由同一条对数正态分布曲线来描述,由此能够获得碳原子簇构型的变化情况。质谱中分布曲线的数目对应于具有不同构型或不同结构稳定性的原子簇的数目。如果某些簇离子的谱峰明显地高出分布曲线,它们的结构应特别稳定,其成簇原子数就是所谓的“奇幻数”（ｍａｇｉｃｎｕｍｂｅｒ）,例如在石墨质谱中的Ｃ＿（６０）就属于这种情况。原子簇的统计分布还与它们的生成过程有关,由此可能揭示出原子簇的产生机理。     

Pt羰基簇合物在NaY内的合成机理

利用IR，EXAFS, ~(13)CO同位素交换反应及与NO作用等手段研究了Pt羰基簇合物[Pt_3(CO)_6]~(2-)_n(n＝3,4)在NaY分子筛超笼内的合成机理．在氧化样品Pt~(2+)/NaY上300－373 K的还愿羰基化过程中，首先Pt~(2+)与CO反应生成PtO(CO)物种(波数σ_(CO)＝2110 cm~(-1))，然后聚集成“Pt_3(CO)_6”(σ_(CO)＝2112，1896和1841 cm~(-1))，最后生成深绿色的Pt羰基簇合物Pt_(12)(CO)_(24)]~(2-)/NaY(σ_(CO)＝2080，1824 cm~(-1))．“Pt_3(CO)_6”的羰基在室温下能迅速地与~(13)CO发生交换，而[Pt_3(CO)_6]~(2-)_n(n＝3,4)的羰基与~(13)CO的同位素交换即使在343 K也进行得很慢，室温下，NO能逐步破坏Pt羰基簇合物的层间和层内Pt－Pt键，得到中间物种“Pt_3(CO)_6”和PtO(CO)，同时在气相产生CO_2和N_2O．而由上述两中间物种出发，300－353 K温度下，在CO气氛中的还原羰基化又能可逆地得到原羰基簇合物．