A population analysis of the bonding in N2O4, B2Cl4, B2F4, C2H4 and C3H4

Population matrices have been calculated from molecular orbital wave functions of N₂O₄, B₂Cl₄, and B₂F₄ in order to understand further the bonding in these molecules which are isoelectronic in valence electrons but different in structure. C₂H₄ and C₃H₄ have been included in this study as check cases.

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Zusammenfassung Ausgehend von Molekülorbitalen werden Besetzungsmatrizen für N₂O₄, B₂Cl₄ und B₂F₄ berechnet, um die Bindung in diesen Molekülen, die in den Valenzelektronen isoelektronisch sind, aber unterschiedliche Strukturen aufweisen, besser zu verstehen. C₂H₄ und C₃H₄ sind in dieser Untersuchung als Prüffälle eingeschlossen.

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Résumé Des matrices d'occupation ont été calculées à partir des orbitales moléculaires de N₂O₄, B₂Cl₄ et B₂F₄, afin de comprendre plus profondément la liaison dans ces molécules, qui sont isoélectroniques par leurs électrons de valence, mais qui n'ont pas la même structure. C₂H₄ et C₃H₄ sont considérés dans cette étude à titre de vérification.

     

The crystal structure of LaIr4B4, ThOs4B4, ThIr4B4 (NdCo4B4-type) and URu4B4, UOs4B4 (LuRu4B4-type)

The crystal structure of LaIr₄B₄ has been refined from single crystal counter data. LaIr₄B₄ is tetragonal,P4₂/n,Z=2, isotypic with NdCo₄B₄, |F|/|F _o|=0.039 for 312 independent reflections [|F _o|>2 (F _o)]. ThIr₄B₄ and ThOs₄B₄ also belong to the NdCo₄B₄-type structure. URu₄B₄ and UOs₄B₄ were found to crystallize with LuRu₄B₄-type structure. The crystal chemistry of (RE)T ₄B₄-phases is discussed and simple geometric relations are shown to exist between them.Dedicated to Prof.B. T. Matthias in celebration of his 60th birthday.     

Conformational preferences of 34 valence electron A2X4 molecules: An ab initio Study of B2F4, B2Cl4, N2O4, and C2O

Ab initio molecular orbital structures and energies of B₂F₄, B₂Cl₄, N₂O₄, and C₂O have been calculated for both perpendicular D_2d and planar D_2h rotamers. The experimental trend toward greater preference for the D_2d forms in going from B₂F₄ to B₂Cl₄ is reproduced. N₂O₄ favors the planar conformation, although the rotation barrier is overestimated at the theoretical levels used. The oxalate dianion is calculated to be more stable in the D_2d conformation; the experimental planar arrangement in the solid may be due to crystal packing forces. The preferences for one conformation over another are small; analysis indicates that different effects may predominate in each case: π stabilization for B₂F₄, hyperconjugation for B₂Cl₄, lone-pair interactions for N₂O₄, and electrostatic repulsions for C₂O.     

B,B, B-Trimethyl-N,N, N-triäthylborazin- und B,B, B-Triäthyl-N,N, N-trimethylborazin-molybdäntricarbonyl

The title compounds have been prepared in low yields starting with cis-(CH₃CN)₃-Mo(CO)₃ or Mo(CO)₆ (photochemical route). The new complexes are generally less stable than the corresponding hexaalkylborazine-chromium compounds and react very smoothly with Lewis bases by cleavage of the borazine-metal bond. The IR.-spectra indicate the similarity of type of bonding in hexaalkylborazine-molybdenum and -chromium complexes.     

Theoretical study of isoelectronic molecules: B6H10, 2-CB5H9, 2,3-C2B4H8, 2,3,4-C3B3H7, and 2,3,4,5-C4B2H6

Isoelectronic molecules regarding B6H10, 2-CB5H9, 2,3-C2B4H8, 2,3,4-C3B3H7, and 2,3,4,5-C4B2H6 are studied by the density functional B3LYP/6-311G(d,p) method and the electron propagator theory in the partial third-order quasiparticale approximation, as well as the extrapolated calculation with the coupled-cluster CCSD(T) theory. The calculated ionization potentials are in good agreement with the experimental data from photoelectron spectroscopy. Valence structures are characterized with natural orbital bond (NBO) theory, exhibiting the multiple three-center two-electron bonds B-H-B, B-B-B, C-B-B, B-C-B, and C-B-C, and chemical bond rearrangements in the cations.     

Electronic structures of the boron cage molecules B4H4, B4Cl4 and B4F4

Ab initio calculations have been performed on B₄H₄, B₄Cl₄ and B₄F₄ in order to aid our understanding of the bonding in these compounds, which is presumably based on a tetrahedral boron cage. This cage has only 8 electrons and so is less than that expected on the basis of the usual framework electron counting rules. Basis sets with polarisation functions were used at the SCF, CI and CPF levels of theory to confirm that the T _d structures are indeed more stable than the D _4h ones. Davidson-Roby population analyses were able to show that many factors, including 3-centre 2-electron bonding and backbonding from the ligand to the boron cage, are of importance in determining the relative stability of the three compounds, of which B₄Cl₄ is the only one that has yet been observed experimentally.     

B4CO2: a new,observable sigma-pi diradical

A new sigma-pi diradical, B4(CO)2, prepared in matrix isolation, was characterized unambiguously by isotopic-substitution infrared spectroscopy and by theoretical computations. Both open-shell singlet and triplet states have three pi electrons but are aromatic with moderately large NICS values. Quantum chemical calculations at various levels indicate that the open-shell singlet is slightly more stable than the triplet state. However, the singlet and triplet are computed to have very similar IR features which do not allow experimental differentiation.     

Photolyse von 2, 2, 4, 4-Tetramethylcyclobutanon-Derivaten

The photochemical reactions of the 2, 2, 4, 4-tetramethylcyclobutanones 1–6 carrying various substituents in 3-position were investigated. The major reaction in alcoholic solution or in the presence of other protic compounds was the formation of the semicyclic acetals 7–12 . Parallel to this reaction decarbonylation occurred, leading to stable cyclopropane derivatives in some cases, depending on the substituents present. Cyclopropanes with an exocyclic double bond underwent ring opening easily or, in case of an exocyclic carbon-nitrogen double bond, added alcohol, thus forming cyclopropane O, N-ketals. Alkyl-acyl biradicals are proposed as common intermediates for both photoreactions. Based on analogy to similar photoreactions reported in the literature, the formation of the semicyclic acetals is assumed to involve a carbene intermediate.     

K2B4O7-Na2B4O7-Li2B4O7-H2O四元体系273 K介稳相平衡

采用等温蒸发平衡法研究了四元体系K2B4O7-Na2B4O7-Li2B4O7-H2O在273 K时的介稳相平衡及平衡液相的密度. 研究发现该四元体系为简单共饱和型, 无复盐及固溶体形成, 根据溶解度数据绘制了相图, 相图中有一个共饱点E, 三条单变度曲线E3E, E2E, E1E; 三个平衡固相分别为K2B4O7·4H2O、Na2B4O7·10H2O 和LiBO2·8H2O. 并简要讨论了实验结果.     

Ternary metal borides [La,Ce,Pr,Nd,Sm] Os4B4 and [Y,La,Ce,Pr,Nd,Sm,Gd,Tb] Ir4B4 with NdCo4B4-type structure

New ternary metal borides with compositionR. E. T ₄B₄ (R. E.=rare earth metal,T=transition metal) have been synthesized within the systems [La,Ce,Pr,Nd,Sm]–Os–B and [Y, La, Ce, Pr, Nd, Sm, Gd, Tb]–Ir–B. All compounds were found to be crystallizing with NdCo₄B₄-type structure. Magnetic measurements (80–300 K,Curie-Weiss behaviour, _p ~ 16K and µ_eff=9.94µ_B for TbIr₄B₄) indicate Y andR. E. elements (except Ce) to be trivalent in these compounds. The crystal chemistry of the isotypic series [Y,R. E.] [Os,Ir]₄B₄ is discussed.

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Ternäre Metallboride. [La,Ce,Pr,Nd,Sm] Os₄B₄ und [Y,La,Ce,Pr,Nd,Sm,Gd,Tb] Ir₄B₄ mit NdCo₄B₄-Struktur

Zusammenfassung Es wurden neue Metallboride der ZusammensetzungR. E. T ₄B₄ (R. E.=Seltenerdmetall,T=Übergangsmetall) innerhalb der Systeme [La,Ce, Pr,Nd,Sm]–Os–B und [Y,La,Ce,Pr,Nd,Sm,Gd,Tb]–Ir–B hergestellt. Alle Verbindungen kristallisieren entsprechend dem NdCo₄B₄-Typ. Magnetische Messungen (80–300K,Curie-Weiss-Verhalten, _p ~ 16K und µ_eff=9.94µ_B für TbIr₄B₄) zeigen an daß Y und dieR. E.-Elemente (ausgenommen Ce) in diesen Verbindungen trivalent sind. Die Kristallchemie der isotypen [Y,R. E.][Os,Ir]₄B₄-Verbindungen wird diskutiert.

     

Mg2Ru5B4 und Mg5Ru13B11, zwei ternäre Magnesium-Rutheniumboride mit Kanalstrukturen

Mg₂Ru₅B₄ and Mg₅Ru₁₃B₁₁, Two Ternary Magnesium Ruthenium Borides with Channel Structures The ternary borides Mg₂Ru₅B₄ and Mg₅Ru₁₃B₁₁, crystallizing in the orthorhombic space group Pbam, were prepared by reaction of the elementary components in sealed tantalum ampoules. Mg₂Ru₅B₄ (a = 1000.0(2) pm, b = 837,6(1) pm, c = 295.42(3) pm, Z = 2, R_W = 0.027 for 563 reflections) is homeotypic with Sc₂Ru₅B₄. The structure contains BRu₆-trigonal prisms, connected by faces and edges to form pentagonal channels filled with chains of magnesium atoms. Mg₅Ru₁₃B₁₁ (a = 2190.1(2) pm, b = 996.7(2) pm, c = 294.65(3) pm, Z = 2, R_W = 0.031 for 959 reflections) has a similar but so far unknown structure in which parts of the magnesium and boron atoms are disordered.     

Total Syntheses of Amphidinolides B1, B4, G1, H1 and Structure Revision of Amphidinolide H2

Nature is a pretty unselective “chemist” when it comes to making the highly cytotoxic amphidinolide macrolides of the B/G/H series. To date, 16 different such compounds have been isolated, all of which could now be approached by a highly convergent and largely catalysis‐based route (see figure). This notion is exemplified by the total synthesis of five prototype members of this family.

     

Syntheses of prodelphinidin B1, B2, and B4 and their antitumor activities against human PC-3 prostate cancer cell lines

Total synthesis of prodelphinidin B1, B2, and B4 has been accomplished. The key step is Lewis acid-mediated equimolar condensations between an epigallocatechin and/or a gallocatechin nucleophile and an epigallocatechin and/or a gallocatechin electrophile. The antitumor effects of synthetic prodelphinidin B1–B4 against human PC-3 prostate cancer cell lines have been investigated. These compounds showed significant antitumor effects. Their activity seemed to be little bit stronger than EGCG and prodelphinidin B3, known antitumor agent.     

从头计算方法比较研究B_2Au_4,Al_2Au_4和BAlAu_4的几何和电子结构(英文)

Au/H相似性的研究是现代化学中的一个热门话题.我们从理论上报道Au/H相似的新成员:共价化合物B2Au4,离子化合物Al2Au4和BAl Au4.采用密度泛函和波函数理论方法对比研究了缺电子体系B2Au4、Al2Au4和BAl Au4的几何和电子结构.详细讨论了它们基态结构的轨道、适应性自然密度划分(Ad NDP)和电子局域函数(ELF)分析.计算结果表明稍微扭曲变形的C2B2Au4是基态结构,在这个共价化合物中含有两个B―Au―B三中心二电子(3c-2e)键.然而C3vAl+(Al Au4)-和C3vAl+(BAu4)-被研究证明是含有三个X―Au―Al三中心二电子键的类盐化合物(在Al2Au4中X=Al,BAl Au4中X=B).Al2Au4和BAl Au4是至今为止首例报道的在离子缺电子体系中含有金桥键的化合物.同时计算了B2Au4-、Al2Au4-和BAl Au4-阴离子基态结构的绝热剥离能和垂直剥离能,为实验表征提供依据.文中报道的金桥键为共价键和离子键相结合的缺电子体系提供了一个有趣的键合模式,有助于设计含有高度分散金原子的新材料和催化剂.     

K2B4O7-Na2B4O7-Li2B4O7-H2O 四元体系15℃介稳相平衡研究

采用等温蒸发平衡法研究了四元体系K2B4O7-Na2B4O7-Li2B4O7-H2O15℃时的介稳相平衡及平衡液相的物化性质(密度,粘度,电导率,折光率,pH)。根据实验数据绘制了相图,相图中有一个共饱点E,三条单变度曲线E3F,E2F,E1F;三个平衡固相分别为：K2B4O7•4H2O,Na2B4O7•10H2O和Li2B2O4•16H2O;硼酸钾具有最大溶解度,硼酸钠具有最小溶解度。同时,根据试验数据绘制了组成－物化性质关系图,从图可见溶液的密度,粘度和折光率均随着溶液浓度的增大而逐渐增大,在共饱和点F处达到最大值,而溶液的pH值和电导率却随着溶液浓度的增大呈总体下降的趋势。