An electronic structure investigation of the BNO-BON-NBO system

The potential energy hypersurface of the ground triplet states of the BNO-BON-NBO system has been investigated using traditional ab initio electronic structure theory. The molecules studied have the molecular formula BON and include three linear and three angular species, and two transition states for the isomerization of an angular N-B-O to an angular B-O-N and a linear B-NO, respectively. All stationary points on the BNO-BON-NBO isomerization potential energy surface have been characterized employing UMP2, UMP4, and Gaussian-2 (G2) theory with the 6-311G(d), 6-311G(2d), and TZ2P basis sets. The isomerization for an angular N-BO to the linear B-NO has a lower energy barrier than that of the former to an angular B-ON. Energetics are presented with G2 energies. Two sets of resonance structures for both bent B-NO (boron nitrosyl) and B-ON (boron isonitrosyl) were proposed and the bonding in the two species was analyzed. For the purpose of comparison, the density functional theory based hybrid methods B3LYP/6-311G(d) and B3LYP/TZ2P have also been applied to both geometry optimization and single-point calculations. It is found that the B3LYP prediction of the nature of the linear B-O is contradictory to that made by all MPn(n = 2 and 4) calculations. The cause for this contradiction is discussed.     

Rhodium-catalyzed arylative cyclization of alkynones induced by addition of arylboronic acids

Alkynones react with arylboronic acids in the presence of a rhodium(I) catalyst to afford four- and five-membered-ring cyclic alcohols equipped with a tetrasubstituted exocyclic olefin. The cyclic allylic alcohol skeleton is constructed by the carbon-carbon bond formation between the carbonyl group and an alkenylrhodium(I) intermediate formed by the regioselective addition of an arylrhodium(I) species across the carbon-carbon triple bond.     

Mono- and diboronates derived from tridentate ONO ligands and arylboronic acids

The syntheses of eight [4.3.0] heterobicyclic boronates containing a N → B coordinative bond are described. The monomeric compounds were prepared by reaction of arylboronic acids with a tridentate ligand having the ONO donor set of atoms. It was shown that substituents at the para-position of the B-phenyl moiety transmit electronic effects to the CN bond which in turn is polarized by formation of the N → B coordination bond. At the same time, related tridentate ligands were also reacted with 1,4-benzenediboronic acid in order to prepare benzene diboron complexes. The structure of this type of compounds was confirmed by X-ray analysis for one of the derivatives.     

Stereoselective synthesis of the C14-C26 fragment of the cytotoxic macrolide FD-891

A stereoselective synthesis of the C₁₄-C₂₆ fragment of the naturally occurring, cytotoxic macrolide FD-891, is described. Asymmetric Evans aldol reactions and aldehyde Brown allylations are key steps of the synthesis.     

New quaternary carbon and nitrogen stabilized polyborides: REB15.5CN (RE: Sc, Y, Ho, Er, Tm, Lu), crystal structure and compound formation

A new family of quaternary carbon and nitrogen containing Rare Earth (RE: Sc, Y, Ho, Er, Tm and Lu) borides: REB_15.5CN, has been synthesized and structurally characterized by powder X-ray diffraction data. They are all isotypic with Sc_1−xB_15.5CN whose structure was solved based on single-crystal X-ray data and HRTEM investigations. The structure refinement converged at a R(F²) value of 0.044 for 364 reflections. The new structure type of Sc_1−xB_15.5CN is composed of a three-dimensional network based on interconnected slabs of boron (B₁₂)^ico icosahedra and (B₆)^oct octahedra. A linear [CBC] chain and nitrogen tightly bridges icosahedra. Sc partially occupies voids in the sheets of boron octahedra. It crystallizes with the trigonal space group P³m1, with Z=2. Lattice parameters (nm) are as follows: for RE: Sc, a,b=0.5568(4), c=1.0756(2); Y, a,b=0.55919(6), c=1.0873(2); Ho, a,b=0.55883(7), c=1.0878(6); Er, a,b=0.55889(5), c=1.0880(6); Tm, a,b=0.5580(1), c=1.0850(6); Lu, a,b=0.55771(9), c=1.0839(4). Magnetic characterization of ErB₁₇C_1.3N_0.6 has been performed.     

X‐Ray Single Crystal Refinement and Superconductivity of La3Ni2B2N3

Crystalline samples of La₃Ni₂B₂N₃ were synthesized using solid state metathesis reactions from combinations of La, LaCl₃, NiCl₂ together with Li₃BN₂. The structure was determined by single crystal X‐ray diffraction (I4/mmm (No. 139), a = 372.95(2) pm, c = 2056.3(2) pm, R₁ = 0.027, wR₂ = 0.062) and confirmed earlier results from neutron powder diffraction. La₃Ni₂B₂N₃ contains BN units capping square planar Ni layers. Isolated nitrogen atoms reside in La₆ octahedra. Magnetic measurements on several bulk samples exhibit superconductivity at temperatures below 14.6 K.     

Orbital correlation effects: The independent pair-potential approximation with application to the ground state and first ionized state of boron hydride

A new method is proposed for calculating correlation effects in atomic and molecular systems. The basis of the method is the formulation of a set of partial configuration expansions which yield directly variational orbital correlation corrections which are appropriately summed in order to obtain an estimate of the total correlation energy. This method is applied to the ground state of boron hydride and its cation at the equilibrium distance of BH. The results of the method are compared in detail with independent electron pair results and second order CI results. It is further shown that multiple substitutions are approximately accounted for in this method and the extent to which they are included is compared with other approximations. Finally, three methods of increasing accuracy, aimed at reducing the necessary computational effort, are given for determining the vertical ionization potential. The most economical method yields an IP of 9.70 eV or 0.03 eV less than the experimental IP. Completion of the basis is estimated to improve this value to 9.77 eV.     

动力学电位法测定硼

本文根据硼酸，苯乙醇酸，孔雀绿形成三元离子缔合型配合物的反应，用孔雀绿离子选择性电极监测反应速率，在最佳实验条件下，用固定时间法，电位变化与硼量在０．２－５．０μｇ／ｍＬ范围呈线性关系，用於测定标准钢样和玻璃标样中的硼，结果与标准值十分接近。     

Electrocatalytic Reduction of Chromium(VI) by Thionin: Electrochemical Properties and Mechanistic Study

The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12 were investigated by cyclic voltammetry at a boron doped diamond(BDD) electrode. A well defined reversible redox couple was observed in acidic, neutral and alkaline solutions. The standard potential and kinetic parameters for thionin were obtained by fitting experimental cyclic voltammograms to those generated by the DigiSim program. The electrogenerated reduced form of thionin has been used as an efficient organic catalyst for the reduction of Cr(VI) at a BDD electrode immersed in aqueous media. The cyclic voltammetry measurements indicate that an electrocatalytic process occurs, where electrochemically generated thionin reduced species (Leucothionin) is oxidized by Cr(VI) back to the parent thionin species via a EC' reaction mechanism. The determination of catalytic rate constant (K_cat) was accomplished again by fitting experimental cyclic voltammograms with simulated ones.