BN Bond Research Articles

Structural aspects of the aromaticity of cyclic π-electron systems with BN bonds

An extension of the HOMA model and Bird's I 6 model for systems with BN bonds is given. Analysis of the aromatic character of 11 pairs of borazine derivatives and their benzene analogues is done based on Cambridge Structural Database (CSD) release using HOMA and I 6 indices. Borazine derivatives exhibit less aromatic character than their benzene analogues and are much less sensitive to the chemical and topological effects from the environment of the rings in question. In contrast to cyclooctatetraene, 1,3,5,7-tetra- t-butyl-2,4,6,8-tetramethyl-1,3,5,7,2,4,6,8-tetraazatetraborocine does not exhibit antiaromatic character.

Tris(triphenylphosphaniminato)boran, B(NPPh3)3

Tris(triphenylphosphoraneiminato)borane, B(NPPh3)3 B(NPPh3)3 has been prepared by the reaction of BF3 · OEt2 with LiNPPh3 in toluene/tetrahydrofuran. Moisture sensitive single crystals of B(NPPh3)3 · 0.5 C7H8 were obtained and characterized by NMR and IR spectroscopy as well as by a crystal structure determination. Space group P21/n, Z = 4, lattice dimensions at –70 °C; a = 2147.8(3), b = 978.5(2), c = 2423.8(2) pm, β = 114.11(1)°, R1 = 0.070. The compound forms monomeric molecules with a planar BN3 skeleton and BN bond lengths of 144.7 pm on average.

Borazane and borazapropellanes: The possibility of inverted tetrahedral boron and nitrogen

The consideration of propellane-like structures whose bridgehead atoms are boron and nitrogen rather than carbon permits a study of B-N bonding and the effects of inverted tetrahedral configurations at these atoms. We analyze these systems primarily by ab initio structure calculation and the atoms-in-molecules properties method. The borazane molecule and its hexamethyl derivative, whose B-N bonds incontrovertibly exist, serve as the starting point. It is found that boraza[3.3.3]propellane resembles hexamethylborazane in its bond length, dipole moment and BN bond critical point. In contrast boraza[2.2.2]propellane does not exist as such but rather has the open form, 1-aza-4-borabicyclo[2.2.2] ctane. Boraza[1.1.1]propellane is found to be kinetically stable in C 3v symmetry; it has a short B-N bond length but no bond critical point of its electronic charge density on the B-N axis.

Cubic boron nitride films grown by low energy B+ and N+ ion beam deposition

We have studied the growth and the properties of BN films prepared by exclusive deposition of mass separated 11B+ and 14N+ ions. BN films grown with ion energies of 500 eV and at substrate temperatures of 350 °C show the IR absorption peak at 1080 cm−1, characteristic for c-BN. These films are nearly stoichiometric and, with transmission electron diffraction, the presence of c-BN nanocrystals was revealed. We compare the growth conditions for ion beam deposition on BN, CN, and diamondlike carbon and propose that the nucleation of nanocrystalline c-BN is related to the ionicity of the BN bond.

Optical and structural characterization of boron nitride thin films

Abstract Thin films of boron nitride were prepared by three deposition methods: r.f. plasma deposition, pulsed laser deposition and r.f. magnetron sputtering. The films were characterized by Fourier transform IR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, optical transmittance spectrophotometry and spectroscopic ellipsometry in the visible-near-UV range. The films are highly transparent with atomic B:N ratios from 2.5 to 1.1, and refractive index values between 1.6 and 1.9 depending on deposition conditions. IR and Raman spectra revealed a short-range atomic order with hexagonal BN bonds, which is more marked in r.f. plasma-deposited films. From the spectroscopic ellipsometric measurements, the optical response of the films was analysed using a two-layer model and applying the Bruggeman effective medium approximation for each layer.

The molecular and solid‐state structure of borazine has been determined at 115 and 160 K by single‐crystal X‐ray crystallography. The molecular structure has C2 symmetry with small deviations from the expected D3h symmetry. The mean value of the BN bond length is 1.429(1) A and the interbond angles of the six‐membered ring are 117.1(1)° at the boron atoms and 122.9(1)°

Borazin im festen Zustand: Verdient es, als “anorganisches Benzol” bezeichnet zu werden?

Darstellung und struktur monomerer N-borylierter Galliumamide

The reaction of N-lithiated aminoboranes of type R 2BN( tBu)Li (R  Me, Mes) with Diorganylgallium chlorides R′ 2GaCl(R′  Me, Et, CH 2C(Ph)Me 2) yields the N-borylated gallium amides R′ 2GaN( tBu)BR 2. A single crystal X ray structure determination did show the molecule Mes 2BN( tBu)GaEt 2 to be monomeric with trigonal planar coordinated gallium, nitrogen and boron atoms. The BN bond length is short (1.384(6) Å), the GaN bond length is rather long (1.937(3) Å), although the nitrogen is non bridging. The described compounds are the first well characterized examples of monomeric gallium monoamides, on the other hand they represent a new class of compounds having two different elements of the III main group bound to one nitrogen atom.

Microwave spectra and structure of hydrogen cyanide-boron trifluoride: an almost weakly bound complex

Rotational spectra of the complex HCN-BF 3 have been observed using pulsed-nozzle Fourier transform microwave spectroscopy. Spectra have been observed for the 11 B and 10 B species with both HC 14 N and HC 15 N, and the hyperfine structure has been analyzed. The complex has the expected C 3υ structure, with the nitrogen end of the HCN toward the boron, but the observed BN bond length of 2.473(29) A is notably shorter than that in the related weakly bound systems N≡N-BF 3 and N≡C-C≡N-BF 3 . The out-of-plane distortion of the BF 3 cannot be determined accurately but is probably less than 3 o

Calculation of NMR Chemical Shifts — The Third Dimension of Quantum Chemistry

AbstractNMR chemical shift calculations provide the basis for an intensive collaboration between quantum chemists and experimentalists. Calculated shift data can be used to describe the magnetic properties of a molecule, to identify unknown compounds by comparison of experimental and theoretical shift values, to determine equilibrium geometries, to investigate conformational changes, to elucidate the mechanism of molecular rearrangements, to determine solvent effects on NMR data, to identify complexation or coordination of soluted molecules by solvent molecules, to detect electronic structure changes caused by the medium, and to describe chemical bonding. This is demonstrated by three examples, namely the determination of the equilibrium structure of the homotropylium cation, the description of BH3NH3 in solution or condensed phases, and the investigation of stannyl cation complexes in solution. IGLO calculations of 13C, 11B, 15N, and 119Sn chemical shifts with DZ+P or TZ+P basis sets lead to the following results: (1) The homotropylium cation possesses an equilibrium 1,7 distance of 2 Å that is indicative of strong through‐space interactions and, as a consequence, homoaromatic character. (2) In solution, the charge transfer from NH3 to BH3 is increased, which leads to a decrease of the BN bond length, an increase of the dipole moment, and a shielding of both the B and the N nucleus. The experimental δ(11B) and δ(15N) values can be reproduced when the geometry effect and the direct solvent effect are included in the shift calculations. (3) Stannyl cations form strongly‐bounded coordination complexes with solvent molecules (binding energy: ≥ 50 kcal/mol) that make the cation properties, in particular δ(119Sn) values, similar to those of covalently‐bounded stannyl compounds. An experimental detection of stannyl cations in solution by NMR spectroscopy should only be possible by extensive solvent variations.

Surface Species on a submicronic boron nitride powder - a starting FT-IR characterization

Surface species on a high specific surface boron nitride powder have been identified by Fourier transform infrared spectroscopy. D 2 and CH 3 OH used as probe molecules allow the characterization of several surface groups: OH and NH groups both coming from the hydrolysis of BN bonds, NH 2 groups whose presence is due to ammonia in the preparation of the BN powder. A few CH 3 groups have also been noticed.

Abinitio study on radical anions of nitro compounds

The results of abinitio molecular orbital calculations on some nitro compounds, RNO2 (R = CH3, CF3, CH2F, BH2, BF2, BHF, C6H5) and on the corresponding radical anions are reported. The geometries of the neutral and charged species were optimized at the SCF and MP2 levels of theory employing the 6-31G* and the 6-31 + G* basis sets. The rotation about the CN and BN bonds reveals distinct conformations for each molecule and vibrational frequencies were determined for such structures. All the employed levels of theory predict structural differences between neutral and charged molecules. The major geometrical changes occurring by electron adding to RNO2 consist in the lengthening of the NO bonds and in the shortening of the CN and BN bonds. The radical anions are calculated to be pyramidal at nitrogen in the stable conformers of CH3NO2−, CF3NO2−, CH2FNO2−, while, for the π-electron-accepting substituents (BH2, BHF, BF2, C6H5), the anion is planar. Electron correlation energy corrections in the framework of Møller–Plesset perturbation theory were included to determine relative stabilities between different conformations. At the MP4/6-31G*//MP2/6-31G* level, an easy rotation of the NO2 group is predicted for all the radical anions and neutral molecules with the exception of BH2NO2−, BF2NO2−, and BHFNO2−, which show high torsional barriers about the BN bond. Keywords: nitro compounds, radical anions, abinitio calculations, molecular structure.

Solvation Effects on Geometry and Chemical Shifts. An Ab Initio/IGLO Reconciliation of Apparent Experimental Inconsistencies on H3B · NH3

To what extent can the structural parameters of a molecule be altered by the surrounding medium? According to model calculations in a polar solvent continuum, the BN bond length in H3B. NH3 in aqueous solution is indicated to be shortened by ca. 0.1 Å over the value in the gas phase (1.672 Å, microwave), i.e. to nearly the BN separation in the solidstate (1.564 Å, X‐ray). Similar calculations with the solvent hexane gave a value of 1.62 Å.

The interband absorption spectra of sputter-deposited boron nitride analyzed using the coherent potential approximation

The visible–near-ultraviolet optical absorption spectra for a family of sputter-deposited boron nitride films are reported here. The spectra of films that are nominally stoichiometric (B/N=1.2–1.3±20%) with short-range order equivalent to hexagonal BN were analyzed using the coherent potential approximation with Gaussian site disorder in the bands, as formulated by Abe and Toyozawa. The relative amount of interlayer BN bond randomness determined from optical measurements is consistent with infrared spectrometry results.

Neue Iminoborane und ihre Reaktionen / Novel Iminoboranes and their Reactions

Abstract The iminoboranes RB≡NR′, 2a-f, are formed by the elimination of Me3SiHal from the corresponding aminoboranes 1a-f. Stabilization occurs either through cyclodimerisation (→3b-d,f), cyclotrimerisation (→4e), bicyclotrimerisation (→5b) or cyclotetramerisation (→6a). Trialkylboranes BX3 are added to give the diboryl amines . 7a-f. The Δ2:-tetraazaborolines . 8a-f, are the (3+2)-cycloaddition products from 2a-f and azides X′N3. A CH-bond of cyclopentadiene adds to one of the BN bonds of 2f, giving a mixture of the corresponding 1,3- and 1,4-cyclopentadienyl boranes. 9f, 9′f.

Beiträge zur Chemie des Bors, 184 Pentacarbonylmetall‐Komplexe des (tert‐Butylimino)‐ (2,2,6,6‐tetramethylpiperidino)borans

(tert‐Butylimino)(2,2,6,6‐tetramethylpiperidino)borane (1) reacts with Cr(CO)6 under photolytic conditions producing pentacarbonylmetal complexes 2. The M(CO)5 fragment coordinates to the tert‐butylimino group. The X‐ray structure analysis of 2a shows an allene type structure with two distinctly different BN bonds (1.29, 1.36 Å) and a long CrN bond (2.22 Å).

Synthesis of Boron Nitride from Triammoniadecaborane and Ammonia

Highly pure boron nitride of low crystallinity could be synthesized from triammoniadecaborane and ammonia below 800°C under atmospheric pressure. Triammoniadecaborane reacted with ammonia at temperatures between 300° and 450°C, and formed an amorphous solid containing BN, NH and BH bonds. According to the data of IR spectrum, the BH absorption band at 2500cm-1 decreased in intensity with increasing temperature, and disappeared at 800°C. The 800cm-1 band assigned to the BNB bonding increased in intensity from 700° to 800°C. The degree of alignment of the B3N3 hexagonal layer increased as the reaction time increased from 2h to 10h at 800°C. The X-ray diffraction profiles of the product formed at 800°C for 10h showed the broad diffractions centered at 2θ=25.5° and 42.0° (Cu Kα). The crystallization of boron nitride synthesized at 800°C for 10h proceeded above 1180°C. The 100 reflection of hexagonal boron nitride was separated from the broad 10 diffraction of the specimen heated at 1550°C for 2h. The lattice constant (c0) and size of crystallite (Lc) of the specimen were 6.735 and 220A, respectively, after heating at 1550°C under atmospheric pressure for 2h. The size of crystallite increased from 320 to 830A as the temperature increased from 1100°C to 1500°C under 2.0GPa for 10min heating. Boron nitride synthesized by heating at 800°C for 10h crystallized to hexagonal boron nitride when heated at 1500°C and 2.0GPa for 10min.

Beiträge zur chemie des bors: CLXXV. Über den einfluss sterischer faktoren auf die konformation von diborylaminen

The aminoborane Ph 2BN(CMe 3SiMe 3 possesses a relatively long BN bond (1.433 Å) and a nonplanar C 2BNCSi (τ(C 2B/NCSi) 45°) skeleton as shown by X-ray structure analysis. In addition, the structure of five diborylamines have been determined by X-ray methods. The compounds (mes 2B) 2NH and (mes 2BNH) 3B belong to diborylamines with a coplanar conformation for the C 2BNHBC 2 (or C 2BNHBN 2) units, while the diborylamines (Ph 2B) 2)NH and (Ph 2B) 2NMe adopt a twist conformation. Finally, an orthogonal conformation was detected for t-Bu 2BNMe-9-borafluorene. The T-Bu 2B group stands almost perpendicular on the BNC-9-borafluorene plane. Consequently, two distinctly different BN bond lengths (1.482 and 1.392 Å) are observed. The influence of steric effects on the conformation and bonding parameters is discussed.

The electronic structure of iminoborane, CH 2NBH 2 and some of its derivatives

Ab-initio calculations at the 6–31G and 6–31G** levels have been performed on the ground state of CH 2NBH 2, (CH 2N) 2BH and (CH 2N) 3B. The perpendicular arrangement of the amino group with respect to the CNB-framework plane is found to be more stable than the coplanar arrangement for all three molecules. Increasing the imino substitution decreases the electron delocalisation of the imino group to boron in the perpendicular configuration (i.e., decreases the dative π-bonding) and thus decreases the energy difference between the two conformations. The accompanying BN bond indices of 1.487, 1.257, and 1.146 for CH 2NBH 2, (CH 2N) 2BH and (CH 2N) 3B, illustrate the decrease in multiple bonding due to the smaller dative π-bonding. In all three species there is a substantial σ-electron drift away from boron to nitrogen coupled with a smaller π-electron back donation. Protonation of iminoborane is predicted to occur at N and the resulting conformation of CH 2NHBH 2 + is planar with a gain in energy of 217 kcal mol −1. Hydride ion addition to iminoborane could occur either at B or C as there is only a small difference in the total energies of CH 3NBH 2 − and CH 2NBH 3 −. Association of CH 2NBH 2 is found to be favourable with the dimerisation energy calculated to be 27.1 kcal mol −1, while the preferred trimerisation process results in a gain in stability of 45.1 kcal mol −1.

Beiträge zur Chemie des Bors, 168 [1] Synthese und Struktur von Azadiboriridinen / Contributions to the Chemistry of Boron, 168 [1] Synthesis and Structure of Azadiboriridines

Two representatives of the three membered B2N-ring system have been obtained by dehalogenation of diborylamines Me3CN[BHalNR2]2. In solution there is no restricted rotation at the exocyclic BN bond, even at low temperature. In contrast, the X-ray structure analysis of the bis-tetramethylpiperidino derivative 10a reveals alternation of short and long BN bonds; one of the tetramethylpiperidino groups stands nearly coplanar with the B2N-ring system, the other, however, is almost perpendicular to the ring plane. The ring contains a short BB bond (1.612 Å).

Methylaminodiphenylborane — Application of 11B, 13C, 14N, 15N NMR

11B, 13C, 14N, 15N NMR is used to study methylaminodiphenylborane (1). Compound 1 can be regarded as a model compound for studying BN(pp)π-. BC(pp)π interactions, for determining the barrier to rotation about the B-N bond and for the application of natural abundance 15N NMR to boron-nitrogen chemistry. The 13C NMR of 1 shows a large splitting of the 13C(para) resonances (in contrast to reports on similar compounds in the literature) as a consequence of hindered rotation about the BN bond. The difference in the 13C(para) nuclear shielding indicates different mesomeric interactions between the trigonal boron atom and the two phenyl groups.