碳硼烷结构规则的量子化学计算

本文对一系列封闭型C_nB_5-n(n=0～5)和C_nB_6-n(n=0～6)碳硼烷骨架及巢型C₄B_5-n(n=0～5)碳硼烷骨架进行了EHMO量子化学计算,根据计算结果讨论了碳硼烷的结构规则.     

碳硼烷硼端衍生物的合成与表征

在路易斯酸催化下,碳硼烷分别与对氰基溴化苄、三苯基膦在甲苯溶液里回流,前者反应中,制备得碳硼烷的硼端与对氰基苄基中的亚甲基直接偶联的产物1,通过调整催化剂的含量,可以显著地提高含B-Cl键的产物2的产率;与三苯基膦的反应中,碳硼烷失去一个硼顶,并与三苯基膦中的P原子直接偶联,生成含B-P键的巢式碳硼烷衍生物3。对此两类化合物进行了核磁、质谱、红外及单晶衍射等表征。化合物1和2中均发现碳硼烷的CH与N形成CH…N氢键和CH…π的弱作用,其中化合物2中,还存在CH…Cl。在巢式化合物3中,发现碳硼烷的CH参与了罕见的CH…HC相互作用。这类反应成功合成了含有B-C、B-Cl、B-P键的碳硼烷衍生物。     

硼烷及杂硼烷簇合物的结构规则

硼烷及杂硼烷簇合物的结构规则张晓辉，陈利平，由业诚，王国栋（大连大学师范学院化学系大连１１６０３５）关键词原子簇化合物，稠合硼烷，杂硼烷，结构规则本文在研究前人工作的基础上［１－１２］，利用徐光宪提出的超额电子数概念，将硼烷分成多个分子片，以讨论它们...     

质子化硼烷正离子体系电子结构的理论研究

本文用a b initio计算法和近似a b initio计算法(PRDDO)研究了质子化硼烷正离子体系的电子结构,给出了一些正离子体系的优化几何构型并讨论了它们的成键情况。计算的硼烷分子质子亲和势与实验值相当吻合。     

14顶点双取代碳硼烷和金属硼烷极化率和二阶超极化率的DFT研究

采用量子化学密度泛函理论(DFT) B3LYP/6-31G(d)方法对14顶点双取代碳硼烷和金属硼烷几何构型进行优化, 结合有限场(FF)方法计算了各体系的极化率和二阶超极化率. 同时金属硼烷中金属原子采用赝势基组进行计算, 讨论基组对计算结果的影响. 结果表明, 14顶点碳硼烷和金属硼烷中碳和金属元素的成键方式不同, 金属硼烷中各原子间距离比碳硼烷中大, 平面偏移角增大. 金属原子的引入有效增加分子的NLO系数, 同时金属硼烷的前线分子轨道能级差比碳硼烷小很多, 金属硼烷材料有可能表现出半导体甚至导体特性, 金属原子采用不同基组对计算结果影响不大.     

确定硼烷的杂硼烷价成键轨道对称性的拓扑方法

本文通过对硼烷的分子轨道的定域化分析, 建立了由硼烷或杂硼烷的骨架多面体的几何性质, 确定其价成键轨道对称性的拓扑方法。从以多面体骨架的三角面和缺顶点周围的边为基约化出的不同约表示中, 按建议的能量与节面数的对应规则,选定出分子的价成键轨道所属的不可约表示。     

确定硼烷的杂硼烷价成键轨道对称性的拓扑方法

本文通过对硼烷的分子轨道的定域化分析, 建立了由硼烷或杂硼烷的骨架多面体的几何性质, 确定其价成键轨道对称性的拓扑方法。从以多面体骨架的三角面和缺顶点周围的边为基约化出的不同约表示中, 按建议的能量与节面数的对应规则,选定出分子的价成键轨道所属的不可约表示。     

硼烷结构规则的量子化学计算

利用EHMO方法,对n=5～12的完整多面体硼烷骨架、缺一个和两个顶点以及戴一个和两个帽原子的各种异构体进行了量子化学计算。直接对硼烷的价成键轨道数公式BMO=4n-[f+3(s+1)]进行了验证。在对计算结果讨论的基础上,进一步探讨了骨架几何结构与成键轨道数之间的关系。     

硼烷簇合物的结构规则

从超额电子数出发，提出了1种稠合型硼烷的结构规则，讨论了各种规则间的关系。     

基于B-H键的活化对含B-C、B-Cl、B-P键的碳硼烷硼端衍生物的合成与表征

在路易斯酸催化下,碳硼烷分别与对氰基溴化苄、三苯基膦在甲苯溶液里回流,前者反应中,制备得碳硼烷的硼端与对氰基苄基中的亚甲基直接偶联的产物1,通过调整催化剂的含量,可以显著地提高含B-Cl键的产物2的产率;与三苯基膦的反应中,碳硼烷失去一个硼顶,并与三苯基膦中的P原子直接偶联,生成含B-P键的巢式碳硼烷衍生物3。对此两类化合物进行了核磁、质谱、红外及单晶衍射等表征。化合物1和2中均发现碳硼烷的CH与N形成CH…N氢键和CH…π的弱作用,其中化合物2中,还存在CH…Cl。在巢式化合物3中,发现碳硼烷的CH参与了罕见的CH…HC相互作用。这类反应成功合成了含有B-C、B-Cl、B-P键的碳硼烷衍生物。     

过渡金属卡宾配合物V.铼的阳离子卡拜配合物与邻-碳硼烷双锂盐的反应及其产物π-环戊二烯基二羰基[(1-碳硼烷基)(苯基)卡宾]铼的晶体结构

铼的阳离子卡拜配合物,[π-C5H5(CO)2ReCC6H5]BBr4(1),在THF中低温下与1,2-碳硼烷双锂盐反应,生成π-环戊二烯基二羰基[(1-碳硼烷基)(苯基)卡宾]铼[π-C5H5(CO)2ReC(C2HB10H10)-C6H5](2)及π-环戊二烯羧基[(1-碳硼烷基甲酰基)(苯基卡拜)铼[π-C5H5(CO)(COC2HB10H10)-ReCC6H5](3),和1与邻-碳硼烷单锂盐反应所生成的产物完全相同.2的分子结构已由单晶X-射线结构分析证实.属于单斜晶系,空间群为P21/n,晶胞参数:a=14.043(8)埃,b=8.302(6)埃,c=17.926(11)埃,β=93.96(5).晶胞中有四个分子.其结构已用重原子法解出并用块矩阵最小二乘法修正,最后的偏离因子R=0.076.同时也讨论了可能的反应机制.     

Metal-Directed Formation of Tetra-, Hexa-, Octa-, and Nonanuclear Complexes of Magnesium,Calcium, Manganese,Copper, and Cadmium

Efficacious metal control of self-assembly of dialkylketipinate dianions leads to completely different supramolecular assemblies. The structures of grid 1 , double-decker 2 , triple-decker 3 , and metalla-spherand 4 were characterized by X-ray crystallographic analyses or by NMR spectroscopy.     

Structural, magnetic, and spectroscopic studies of YAgSn, TmAgSn, and LuAgSn

The rare earth-silver-stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P6₃mc, Z=2, a=468.3(1), pm, wR₂=0.0343, 353 F² values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a=726.4(2), , wR₂=0.0399, 659 F² values, 15 variables for TmAgSn, and a=723.8(2), , wR₂=0.0674, 364 F² values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with , in order to clarify the silver-tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag-Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag-Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie-Weiss paramagnet with an experimental magnetic moment of 7.2 μ_B/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by ¹¹⁹Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental ¹¹⁹Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag-Sn bonds and also significant Ag-Ag bonding in LuAgSn.     

Theoretical Study of Molecular Structure,Reactivity, Lipophilicity,and Solubility of N-Hydroxyurea,N-Hydroxythiourea,and N-Hydroxysilaurea

Ab initio molecular orbital methods at the CBS-QB3 level of theory have been used to study the structure and gas-phase stability of various tautomers and rotamers of N-hydroxyurea, N-hydroxythiourea, and N-hydroxysilaurea, their anions and protonated forms. The geometries of N-hydroxyurea, N-hydroxythiourea, and N-hydroxysilaurea, their anions and cations were optimized at the Becke3LYP/CBSB7 level of theory. For all compounds studied, the amidic form is computed to be substantially more stable than the iminolic tautomer. N-Hydroxyurea and its thio and sila derivatives are computed to behave as Nacids in the gas phase. These compounds are in gas-phase weak acids with a calculated acidity of about 1425 to 1355 kJ-mol^–1. Basicities increase in the order: N-hydroxyurea < N-hydroxythiourea < N-hydroxysilaurea. The most stable protonated structures are represented by several isomers with almost equal stability. Thus, in the N-hydroxyurea, N-hydroxythiourea, and N-hydroxysilaurea, both protonation at the double bonded (C=O, C=S and Si=O) oxygen and sulfur atoms, as well as the protonation at the N(H)OH nitrogen basic center is equally probable. The experimental pK _a value (10.6) of N-hydroxyurea and the computed value (9.7) for its monohydrated complex with the specifically hydrogen-bonded water molecule to the ionizable OH group are in a good agreement. The experimental partition coefficient of N-hydroxyurea is best reproduced by the Alog P_s method. The formation of nitroxide radical in the reaction of N-hydroxyurea and its sulfur and silicon substituted derivatives with the phenol radical is an exothermic process. Thus, the \bondN(H)OH moiety of these compounds may quench the structurally related tyrosyl radicals in the active site of ribonucleotide reductase.     

Synthesis and characterization of metal-centered, six-membered, mixed-valent, heterometallic wheels of iron, manganese, and indium

Heptanuclear metal-centered, six-membered, mixed-valent, heterometallic wheels 1-3 of iron, manganese, and indium were prepared in a one-pot reaction from N-benzyldiethanolamine (H2L(1)), cesium carbonate, [PPh4]2[MnCl4], and FeCl3 or InCl3. All three complexes were characterized by the combination of elemental analysis, FAB mass spectroscopy, X-ray diffraction and cyclic voltammetry and in the case of 1 additionally by M?ssbauer spectroscopy. In 1, four Mn(II) ions in the periphery are arranged in pairs alternating with one Fe(III) ion each, with an Fe(III) ion located in the center. In 2, three Mn(II) ions alternate with three In(III) ions, whereas in 3, four In(III) ions are arranged in pairs and alternate with one Mn(II) ion each. In 2 and 3 an Mn(II) ion is encapsulated in the center.     

Synthesis of yttrium,lanthanum, neodymium,praseodymium, and lutetium alkoxides and acetylacetonates

A convenient and practical method is proposed for the synthesis of lanthanide and yttrium alkoxides. The method involves dissolving the metals or their hydrides in a solution of dry HCl in the corresponding alcohol, with subsequent dehalogenation of the LnCl₃ solution by an equivalent amount of alkali metal (Na, Li), The rareearth alkoxides are easily converted into acetylacetonates Ln(acac)₃ by the action of acetylacetone.A. N. Nesmeyanov Institute of Elementoorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2490–2493, November, 1992.     

Transition-metal-free O-, S-, and N-arylation of alcohols, thiols, amides, amines, and related heterocycles

A new protocol for the Ullmann-type arylation process of different aromatic heterocycles without any transition-metal catalyst, implying the use of a combination of an excess of potassium hydroxide and dimethyl sulfoxide, is described. The reaction can be performed between a broad range of starting nucleophiles including phenol, alcohols, amines, nitrogen-containing five-membered systems such as pyrazoles, imidazoles, and indoles, and amides with haloarenes, iodide and bromide derivatives giving the best results, the possible pathway involving the in situ generation of the corresponding benzyne intermediate. When the reaction was performed with 2-iodoaniline and either carboxamides or isothiocyanato derivatives, the corresponding benzoazole derivatives were obtained.     

Structure and properties of HOO,HOS, HSO,HSS, FSO,FOS and FSS

High quality SCF-MO calculations are reported for the title molecules, including geometry optimization. One-electron properties are presented and discussed, and relative stabilities of (HOS, HSO) and (FOS, FSO) compared. Little experimental geometric data are available at present, but the calculated and experimental geometries of HO₂ agree well.     

Electronic structure, spectra, and magnetic circular dichroism of cyclohexa-, cyclohepta-, and cyclooctapyrrole

Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained.