BN Bond Research Articles

Ar Implantation at the hBN/Rh(111) Nanomesh by ab Initio Molecular Dynamics

The controlled intercalation of selected species underneath graphene or hexagonal boron nitride (hBN) on a substrate opens new ways for the functionalization and the tuning of properties of these systems. In this work, the case of hBN on rhodium exposed to a low-energy Ar-ion beam [Cun et al., Nano Lett. 2013, 13, 2098–2103] is further considered theoretically. With the help of ab initio molecular dynamics, the structural rearrangements induced by the interaction between the impacting Ar ion and the substrate are investigated. It is shown that the ion can be intercalated and trapped between the metal and hBN by breaking some BN bonds and penetrating the overlayer. The resulting defective structure relaxes quickly, while Ar moves to a stable site where a protrusion appears on top of the characteristic super honeycomb lattice of the nanomesh. The presented results provide a first atomistic description of the complex processes leading to the formation of the, so-called, boron nitride nanotents.

Highly selective and sensitive detection of F− and CN− ions simultaneously by a reaction-based BODIPY-containing conjugated polymer

A new BODIPY-containing conjugated polymer (P1) had been designed and synthesized as a colorimetric and fluorescent chemosensor for F− and CN−. The combination of advantages of both reaction based sensors and conjugated polymer sensors offered its highly sensitive and selective recognition of F− and CN− with no interference from each other. The addition of F− and CN− to P1 solution induced a rapid color change from purple to orange and faint yellow, respectively. At the same time, the emission color of the P1 solution changed from red to yellow and yellowish green in presence of F− and CN−, respectively. 11B, 19F and 1H NMR spectra indicated that addition of fluoride and cyanide result in a nucleophilic displacement to break a BN bond of P1. In addition, the cell imaging experiments demonstrated that P1 could be successfully applied as a bioimaging agent with good biocompatibility.

B═N Bond Cleavage and BN Ring Expansion at the Surface of Boron Nitride Nanotubes by Iminoborane

A new feature of reactivity of iminoborane (HBNH) at the surface of boron nitride nanotube has been revealed by this theoretical study. The HBNH molecule not only selectively breaks the B═N double bond of the BN nanotubes (BNNTs) but also expands the hexagonal network of the tube to larger cages at the surface. Such expanded structures are stabilizing by 30–50 kcal/mol depending on the chirality and reactive site of the tubes. Complexation energy decreases with diameter (because of the strain effect) of the tube and is lowest for a planar BN-sheet. However, a [2+2]-cycloaddition reaction that is common for iminoborane is also exhibited depending on the site and chirality. For zigzag tube, diagonal BN bonds, either at the edge or at the middle of the tube, are cleaved, but BN bonds parallel to the tube axis undergo cycloaddition reactions. In contrast, diagonal BN bonds of the armchair BN-tube prefer cycloaddition and bonds perpendicular to the tube axis follow this new reactivity pattern. Transition state...

Novel structure and abnormal electronic properties of ultra-thin BC2N nanotubes from first-principles investigation

Here, we employed first-principles calculations to investigate the structure, stability and electronic properties of ultra-thin BC2N nanotubes. We obtained a novel, screwy, helicoidal and cyclical (as the structure of DNA molecule) structure that had not been reported in previous studies. Further, we found the stability of ultra-thin BC2N nanotubes depends on not only the number of BN bonds but also the arrange modes of CNT and BNNT segments. Our results also showed the electronic properties of ultra-thin BC2N nanotubes are tunable and abnormal when compared to the relative big ones.

A simple precursor pyrolysis route to BCN nanoflakes

Bulk quantity hexagonal borbon carbon nitride (BCN) nanoflakes were successfully synthesized via a simple precursor pyrolysis method. Scanning electron microscope (SEM) and high resolution transmission electron microscopy (HR-TEM) showed the nanoflakes having tens of layers with the size of 20μm and 10nm in thickness. Fourier transform infrared (FT-IR) and X-ray photoelectron spectrometer (XPS) were performed to reveal the chemical structure of the products. The results show that the products have a hybrid chemical composition of BN, CC, and CN bonds.

Square- and hexa-cross sectional carbon and boron-nitride nanoneedles – A theoretical study

Square- and hexa-cross sectional carbon nanoneedles and their boron-nitride counterparts are investigated as a new class of nanomaterials. In contrast with the ordinary carbon nanotubes, the band gaps of the introduced carbon nanoneedles are not strongly dependent on the size of the cross sections, whereas for the boron-nitride needles such a dependency is not observed. Note that any attempts to optimize the octa-cross sectional nanoneedles, change the structure to an ordinary nanotubes; therefore it seems that octa-cross sectional nanoneedles could not be synthesized. Topological analysis also indicates that although CC bonds have covalent nature, the BN bonds show ionic character.

Vibrational Analysis of Zigzag and Armchair Fixed Free Single Walled Boron Nitride Nanotubes: Atomistic Modeling Approach

This paper illustrates the vibrational behavior of single walled boron nitride nanotubes (SWBNNTs) using finite element method (FEM). To this end, atomistic model for both zigzag and armchair chiralities of the single walled boron nitride nanotubes for fixed-free boundary condition is analyzed and their natural frequencies and corresponding mode shapes are obtained. The fixed-free SWBNNTs with different aspect ratios (length/diameter) for both types of chairality are modeled as space frames by considering three dimensional elastic beams and point masses. The elastic properties for beam element are considered based on mechanical characteristics of the BN bond in the hexagonal lattice. The masses of B and N atoms are assumed as point masses at the ends of BN bond. Implementing the finite element simulation approach, the natural frequencies of fixed-free SWBNNTs are computed. Results pertaining to bending, torsional and axial modes of vibration are reported with discussions. The present approach is found to be time saving and different chiralities can be easily incorporated in terms of real atomic structures. The results shows, that as the size of fixed free SWBNNTs in terms of length as well as diameter increases the natural frequencies of free vibration decreases, and the zigzag form of fixed-free SWBNNTs are more sensitive compare to armchair form. Keywords: Atomistic model, single walled boron nitride nanotubes, vibrational analysis, FEM, frequency, mode-shapes.

A coupled-cluster study of linear and rhombic boron nitride dimers: a revisit

The potential energy surfaces of both singlet and triplet B2N2 have been investigated computationally at the coupled-cluster level with a polarized triple zeta basis set augmented with diffuse functions. Calculated vibrational frequencies and intensities are also reported. The triplet species are consistently more stable than their singlet analogs and the stabilities of the linear B2N2 isomers increase with increasing number of B–N bonds. The most stable isomer is the linear triplet BNBN isomer with a rhombic form with a short diagonal BB distance close in energy. Our results are consistent with the results of the matrix IR studies of Andrews et al. nucleus-independent chemical shift (NICS) values were calculated for the singlet D2h rhombic form and its C2v dication, and these were compared to those of the D2h cyclobutadiene and its D2d dication, respectively. Electron density plots for the linear and rhombic B2N2 minima showed similar distributions for the singlet and triplet states. These plots confirmed weak BB bonding interactions in both rhombic forms but larger BN bond orders.

B=N Bonds and BCN Rings – Reactivity and Charge Density Studies

Abstract (F5C6)2BNMe2 (1) was prepared and (F3C)2BNMe2 (2) was resynthesized. The crystal structures of both compounds were determined. In contrast to 2, compound 1 does not react with diazomethanes under carbine insertion into the BN bond. In this way the known (F3C)2BCH(SiMe3)NMe2 (3) was resynthesized from 2 and its solid‐state structure was determined. The electron densities of compounds 1, 2, and 3 and those of the simpler model compound (F3C)2BCH2NMe2 (4) as well as that of the BN/CC isoelectronic compound (F3C)2CCH2CMe2 (5) for comparison were calculated and their topologies analysed in terms of the Quantum Theory of Atoms in Molecules (QTAIM). Despite 2 has a shorter B–N bond in calculations and in the crystal than 1, the atomic charges and electron density parameters to QTAIM are very similar for both compounds and cannot explain the different reactivity. The three‐membered rings 3 and 4 do not show bond‐critical points for their B–N bonds. The nature of the B–N bond region was also analysed in terms of the source function contributions in QTAIM, which demonstrated the importance of the close proximity of a third atom in three‐membered rings for the charge density topologies in such systems.

BN-substituted diphenylacetylene: a basic model for conjugated π-systems containing the BN bond pair

We report the synthesis, structural characterization, and optoelectronic properties of BN-Tolan 1 and Bis-BN-Tolan 2, one of the simplest conjugated systems containing the BN bond pair. BN-tolans 1 and 2 display absorption and emission properties that are distinct from their carbonaceous analogue, tolan. In addition, Bis-BN-Tolan 2 exhibits unique N–H⋯π(C≡C) hydrogen bonding in the solid state.

Epitaxial Growth of Hexagonal Boron Nitride on Ir(111)

The formation of a hexagonal boron nitride (h-BN) layer through dissociation of borazine (B3N3H6) molecules on Ir(111) has been investigated by a combination of X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, temperature-programmed desorption, and low-energy electron diffraction. At low temperature (T = 170 K), molecular borazine adsorption occurs with the plane of the benzene-like ring parallel to the substrate. Dehydrogenation is observed at temperatures higher than 250 K and extends up to 900 K, with a maximum H2 desorption rate around 300 K. Besides dehydrogenation, room temperature adsorption of borazine leads to the formation of atomic and molecular fragments due to the break-up of part of the BN bonds. The epitaxial growth of h-BN starts at temperature higher than 1000 K where an extended and long-range ordered layer is obtained. The presence of a corrugation in the h-BN layer with moire periodicity of (13 × 13)/(12 × 12) BN/Ir unit cell is reflected in the double compo...

R.F. Magnetron Sputtering of Multilayered c-BN Films on Cemented Carbide Tool

A c-BN thin film was deposited using a B4C target in a r.f. magnetron sputtering system. The c-BN layer was coated with a TiAIN adhesion layer (approximately 2 microm), boron carbide (approximately 1 microm) and BCN (10 approximately 15 nm) nano-gradient layer system. The c-BN layers with thicknesses of more than 0.5 microm were successfully deposited onto cemented carbide substrates. The high resolution XPS spectra analysis of B1s and N1s revealed that the c-BN film was mainly composed of sp3 BN bonds.

Oxygen-induced magnetic properties and metallic behavior of a BN sheet

In this paper, an ab initio method has been employed to study the adsorption energies,electronic structures and magnetic properties of a BN sheet functionalized byan oxygen (O) atom. The adsorption process is typically exothermic, and someunusual properties can be revealed with different adsorption sites. The energygap of the BN sheet narrows due to the strong hybridization between O and BNelectronic states when the O locates above a BN bond or a nitrogen atom. Uponthe adsorption of O above a B3N3 ring or a boron atom, the electrons of theO-adsorbed BN system are polarized, which gives rise to a magnetic moment of 2.0μB. In this case, the Fermi level crosses the valence band, resulting in the O-adsorbed BNsystem being metallic. Furthermore, potential energy curve analysis shows that themagnetism and metallicity of the BN system can be modulated by the externaltemperature and pressure.

Dehydrogenation of Saturated CC and BN Bonds at Cationic N-Heterocyclic Carbene Stabilized M(III) Centers (M = Rh, Ir)

Chloride abstraction from the group 9 metal bis(N-heterocyclic carbene) complexes M(NHC)(2)(H)(2)Cl [M = Rh, Ir; NHC = IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene or IMes = N,N'-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] leads to the formation of highly reactive cationic species capable of the dehydrogenation of saturated CC and BN linkages. Thus, the reaction of Ir(IPr)(2)(H)(2)Cl (1) with Na[BAr(f)(4)] in fluorobenzene generates [Ir(IPr)(2)(H)(2)](+)[BAr(f)(4)](-) (4) in which the iridium center is stabilized by a pair of agostic interactions utilizing the methyl groups of the isopropyl substituents. After a prolonged reaction period C-H activation occurs, ultimately leading to the dehydrogenation of one of the carbene (i)Pr substituents and the formation of [Ir(IPr)(IPr'')(H)(2)](+)[BAr(f)(4)](-) (5), featuring the mixed NHC/alkene donor IPr'' ligand. By contrast, the related IMes complexes M(IMes)(2)(H)(2)Cl (M = Rh, Ir), which feature carbene substituents lacking beta-hydrogens, react with Na[BAr(f)(4)] in fluorobenzene to give rare examples of NaCl inclusion compounds, viz., [M(IMes)(2)(H)(2)Cl(Na)](+)[BAr(f)(4)](-) (M = Rh, 6; M = Ir, 7). Intercalation of the sodium cation between the mesityl aromatic rings of the two NHC donors has been demonstrated by crystallographic studies of 7. Synthetically, 6 and 7 represent convenient yet highly reactive sources of the putative 14-electron [M(NHC)(2)(H)(2)](+) cations, readily eliminating NaCl in the presence of potential donors. Thus 7 can be employed in the synthesis of the dinitrogen complexes [Ir(IMes)(2)(N(2))(2)](+)[BAr(f)(4)](-) (8a) and [Ir(IMes)(2)(N(2))THF](+)[BAr(f)(4)](-) (8b) (albeit with additional loss of H(2)) by stirring in toluene under a dinitrogen atmosphere and recrystallization from the appropriate solvent system. The interactions of 6 and 7 with primary, secondary, and tertiary amineboranes have also been investigated. Although reaction with the latter class of reagent simply leads to coordination of the amineborane at the metal center via two M-H-B bridges {and formation, for example, of the 18-electron species [M(IMes)(2)(H)(2)(mu-H)(2)B(H).NMe(3)](+)[BAr(f)(4)](-) (M = Rh, 9; M = Ir, 10)}, the corresponding reactions with systems containing N-H bonds proceed via dehydrogenation of the BN moiety to give complexes containing unsaturated aminoborane ligands. Thus, for example, 6 catalyzes the dehydrogenation of R(2)NH x BH(3) (R = (i)Pr, Cy) in fluorobenzene solution (100% conversion over 6 h at 2 mol % loading) to give R(2)NBH(2); the organometallic complex isolated at the end of the catalytic run in each case is shown to be [Rh(IMes)(2)(H)(2)(mu-H)(2)BNR(2)](+)[BAr(f)(4)](-) (R = (i)Pr, 11; R = Cy, 12). In contrast to isoelectronic alkene donors, the aminoborane ligand in these complexes (and in the corresponding iridium compounds 13 and 14) can be shown by crystallographic methods to bind in end-on fashion via a bis(sigma-borane) motif. Similar dehydrogenation chemistry is applicable to the primary amineborane (t)BuNH(2) x BH(3), although in this case the rate of rhodium-catalyzed dehydrogenation is markedly slower. This enables the amineborane complex [Rh(IMes)(2)(H)(2)(mu-H)(2)B(H) x NH(2)(t)Bu](+)[BAr(f)(4)](-) (15) to be isolated at short reaction times (ca. 6 h) and the corresponding (dehydrogenated) aminoborane system [Rh(IMes)(2)(H)(2)(mu-H)(2)BNH(t)Bu](+)[BAr(f)(4)](-) (16) to be isolated after an extended period (ca. 48 h). As far as further reactivity is concerned, aminoborane systems such as 14 show themselves to be amenable to further dehydrogenation chemistry in the presence of tert-butylethylene leading ultimately to the dehydrogenation of the boron-containing ligand and to the formation of a directly Ir-B bonded system described by limiting boryl (Ir-B) and borylene (Ir=B) forms.

Wear Resistance of c-BN Surface Modified 316L Austenitic Stainless Steel by R.F. Sputtering

Cubic boron nitride (c-BN) is a promising material for use in many potential applications because of its outstanding physical properties such as high thermal stability, high abrasive wear resistance, and super hardness. Even though 316L austenitic stainless steel (STS) has poor wear resistance causing it to be toxic in the body due to wear and material chips, 316L STS has been used for implant biomaterials in orthopedics due to its good corrosion resistance and mechanical properties. Therefore, in the present study, c-BN films with a layer were applied to a 316L STS specimen in order to improve its wear resistance. The deposition of the c-BN films was performed using an r.f. (13.56 MHz) magnetron sputtering system with a target. The coating layers were characterized using XPS and SEM, and the mechanical properties were investigated using a nanoindenter. The friction coefficient of the c-BN coated 316L STS steel was obtained using a pin-on-disk according to the ASTM G163-99. The thickness of the obtained c-BN and were about 220 nm and 630 nm, respectively. The high resolution XPS spectra analysis of B1s and N1s revealed that the c-BN film was mainly composed of BN bonds. The hardness and elastic modulus of the c-BN measured by the nanoindenter were 46.8 GPa and 345.7 GPa, respectively. The friction coefficient of the c-BN coated 316L STS was decreased from 3.5 to 1.6. The wear property of the c-BN coated 316L STS was enhanced by a factor of two.

On the nature of the B⋯N interaction and the conformational flexibility of arylboronic azaesters

It is shown that the structural and physicochemical properties of arylboronic azaesters result from the properties of the key B-N bond. This bond is different in arylboronic azaesters from typical single/double/triple B-N bonds present in other boron-nitrogen compounds. By studying a model example, 6-tert-butyl-2-(3',5'-difluorophenyl)-(N-B)-1,3,6,2-dioxazaborocane, it is proved that the molecule adopts the closed form in the solid state with the BN bond length equal to 1.7646(3) Å. This represents the longest B-N bond length for an arylboronic ester reported in literature. According to the results of experimental charge density studies and QTAIM analysis, the BN bond/contact shows good separation of the respective atomic basins and significant flexibility. The source function and NBO analyses indicate an evident involvement of the oxygen atoms in the creation of the B-N bonding. According to our DFT calculations the isolated model molecule exists in the open conformer. The constrained energy scans reveal an E(d(B-N)) potential energy surface which depends strongly on the nature of the substituents at the nitrogen and aromatic carbon atoms. It appears that an appropriate substitution can produce either conformer. A dipole moment analysis provides a good insight into the reactivity properties of the compound in solution. The opening of the azaester cage is associated with a breaking of the B-N bond, thus decreasing the magnitude of the dipole moment. The existence of the open conformer is confirmed by multi-temperature NMR studies. When decreasing the temperature of the measurements the (1)H and (11)B NMR spectra show features corresponding to the open form of the model arylboronic azaester.

Structural and Spectroscopic Properties of Aryl Substituted Aminoboranes as Model Compounds and Synthons for B/C/N Materials and New Fluorescent Systems

AbstractTetraphenylaminoborane (1) and carbazonyldiphenylborane (2) are examples for isolated BN bonds completely substituted by aryl ligands, which enable π‐interactions. Such systems can serve as building blocks for new fluorescent polymers and are also suitable precursors for B/C/N materials. The compounds were characterized by multinuclear NMR spectroscopy, UV/Vis spectroscopy, and single‐crystal X‐ray diffractometry. Both compounds 1 and 2 are principal structures for tricoordinate, aryl substituted BN bonds. Compound 1 crystallizes in the monoclinic crystal system in the space group P21, with two formula units per unit cell with a = 9.8236(9) Å, b = 9.2743(8) Å, c = 10.7426(10) Å; α = 90°, β = 107.228(4)°, γ = 90°, Z = 2, V = 934.81(15) Å3 (final R indices [I > 2 σ(I)]: R1 = 0.0597; wR2 = 0.1489) and compound 2 crystallizes in the monoclinic crystal system of the space group C2/c. The unit cell contains four formula units as a set of two pairs of diastereomers. The cell parameters are a = 17.404(4) Å, b = 11.020(2) Å, c = 9.4195(19) Å; α = 90°, β = 91.45(3)°, γ = 90°, Z = 4, V = 1805.9(6) Å3 (final R indices [I > 2 σ(I)]: R1 = 0.038; wR2 = 0.0847). The UV/Vis spectra of 1 and 2 reveal strong absorptions (240 nm and 285 nm) for 1 and broad features (260 nm and 290 nm) for 2. The 11B NMR spectroscopic data of 1 (48.7 ppm) and 2 (53.0 ppm) clearly indicate tricoordinate BN systems in solution with a weaker BN π‐interaction compared to dialkylborylamines.

The Molecular Structure of 1,3,5,7- Tetra(tert-butyl)-2,4,6,8-tetra(chloro)- borazocine [1

The borazocine (ClB=NCMe3)4 crystallizes in the monoclinic system, space group C2/c with Z = 6, i. e. there are two independent molecules in the unit cell. The first molecule has no crystallographic symmetry, while the second molecule is characterized by a twofold axis which generates the (ClB= NCMe3)4 molecule from the fragment (ClB=NCMe3)2. The molecules are tub-shaped showing alternating longer and shorter B-N bonds. Compared with the borazocine (N3B= NCM3)4 the BN bonds of (ClB=NCMe3)4 are on average shorter than those of the azide derivative. Although B-N bond lengths and N-B-N and B-N-B bond angles in both molecules of (ClB=NCMe3)4 are identical within the limits of the standard deviation, the opposite B2N2 planes differ significantly for the two independent molecules.

Fundamental Thermochemical Properties of Ammonia Borane and Dehydrogenated Derivatives (BNHn, n = 0−6)

The heats of formation for BN, HBNH, H2BNH2, and H3BNH3 and their radicals, anions, cations, and protonated species were predicted using the CCSD(T) method with correlation consistent basis sets extrapolated to the complete basis set and core−valence, scalar relativistic, spin−orbit, and zero-point energy corrections. Chemical accuracy (±1 kcal/mol) is obtained for these heats of formation, allowing reliable results for electron and hydride affinities, ionization energies, basicities (neutral proton affinities), acidities (anion proton affinities), and bond dissociation energies of the BNHn (n = 0−6) molecules. The closed shell BNHn molecules, except for H3BNH3 (double diffuse functions on B and N required), do not bind an electron and behave as nitrogen acids and bases. Protonation of H3BNH3 leads to nearly spontaneous H2 release. The closed shell BNHn species exhibit ionization energies similar or smaller than those of hydrocarbons, and for the H2BNH radical, its ionization energy (∼5.9 eV) is close to that of the alkali elements. Except for H3BNH3, the NH bonds are systematically stronger than the BH bonds, and the BDE(NH) values tend to increase with increasing multiple character of the BN bonds. Trends and comparisons between properties obtained through reactions on the N and B atoms are given. Comparisons with properties of hydrocarbons show similarities and differences between the two isoelectronic series.

The Molecular Structure of 1,3,5,7- Tetra(tert-butyl)-2,4,6,8-tetraazidoborazocine [1

The tetra(tert-butyl)-tetraazido-borazocine, 1, has the expected tub shape as determined for (SCNB=NtBu)4. However, it crystallizes in the triclinic system and shows no symmetry element in contrast to the isothiocyanato derivate which has C2 symmetry. There are two kinds of BN bonds which alter from long to short (average 1.491 and 1.388 A° ). The BN bond lengths to the azido groups are, on average, 1.486 °A. All B and N atoms of the ring reside in a trigonal planar environment. The B-N-N bond angles are close to 120◦ showing that the central nitrogen atom can be considered as sp2-hybridized. The N-N-N bond angles are on average 173.6◦. The two sets of the opposite B2N2 planes include an angle of 114.8◦. The atoms of the azido groups are almost coplanar with the respective NBN planes. This together with the short BN(N2) bond lengths indicates that these azido groups are π-bonded to their corresponding boron atom.