B3N3 Ring Research Articles

Thermoelectric properties of graphene through BN-ring doping: A theoretical investigation

Although graphene presents excellent transport properties, its potential for thermoelectric applications is still limited due to its low Seebeck coefficient and high thermal conductivity. Efforts to enhance its thermoelectric properties have involved the usage of carbon-based nanoribbons (Zheng et al., 2012; Hossain et al., 2016) [1,2], strain engineering (Nguyen et al., 2015), and heteroatom co-doping, particularly with nitrogen and/or boron atoms (Wang et al., 2018) [3]. In this work, multiscale simulation approaches combining density functional theory calculations and semi-empirical models are used to investigate the thermoelectric properties of graphene via borazine (B3N3)-ring doping. In particular, the bandgap engineering obtained by this doping technique (Caputo et al., 2022) can separate opposite electron and hole contributions and therefore results in a significant enhancement of the Seebeck effect and, accordingly, of the power factor. The results obtained are not only dependent on the concentration of B3N3 rings but are also notably influenced by their orientation configuration. Furthermore, the effects of distribution and rotational disorders are also considered, clarifying the thermoelectric properties of realistic systems. Lastly, the thermal lattice conductance is estimated revealing a substantial reduction of up to 40% compared to pristine graphene opening up the possibility of enhancing the thermoelectric efficiency of BNC materials. The present theoretical approach highlights how BN-ring doping can refine the thermoelectric properties of graphene, offering a pathway for enhancing its suitability in practical thermoelectric applications.

Benzene and Borazine, so Different, yet so Similar: Insight from Experimental Charge Density Analysis.

Although benzene and borazine are isoelectronic and isostructural, they have very different electronic structures, mainly due to the polar nature of the B-N bond. Herein, we present an experimental study of the charge density distribution obtained from the multipole model formalism and Hirshfeld atom refinement (HAR) based on high-resolution X-ray diffraction data of borazine B3N3H6 (1) and B,B',B″-trichloroborazine (2) crystals. These data are compared to those obtained from HAR for benzene (4) and 1,3,5-trichlorobenzene (5) and further compared with values obtained from density functional theory calculations in the gas phase, where N,N',N″-trichloroborazine (3) was also included. The results confirm that, unlike benzene, borazines are only weakly aromatic with an island-like electronic delocalization within the B3N3 ring involving only the nitrogen atoms. Furthermore, delocalization indices and interacting quantum atom energy for bonded and non-bonded atoms were found to be highly suitable indicators capable of describing the origin of the discrepancies observed when the degree of aromaticity in 2 and 3 is evaluated using common aromaticity indices. Additionally, analysis of intermolecular interactions in the crystals brings further evidence of a weakly aromatic character of the borazines as it reveals surprising similarities between the crystal packing of borazine and benzene and also between B,B',B″-trichloroborazine and 1,3,5-trichlorobenzene.

Surface-Controlled Conversion of Ammonia Borane from Boron Nitride

“One-pot regeneration”, which is simple regneneration method of ammonia borane (AB) using hydrazine and liquid ammonia, enables conversion of AB from hexagonal boron nitride (h-BN) after milling hydrogenation. Solution 11B-NMR revealed the presence of AB after NH3/N2H4 treatment of milled h-BN (BNHx) although the yield of AB was less than 5%. The conversion mechanism was clarified as B-H bonds on the h-BN surface created by ball-milling under hydrogen pressure have an ability to form AB, which was confirmed by Thermogravimetry-Residual Gas Analysis (TG-RGA) and Infrared (IR) analysis. The reaction routes are also the same as regeneration route of polyborazylene because intermediates of AB such as (B(NH2)3 and hydrazine borane were found by solution 11B-NMR after soaking BNHx in liquid NH3 and hydrazine, respectively. Because of the fact that all reactions proceed on the h-BN surface and no reaction proceeds when neat h-BN is treated, breaking of B3N3 ring structure and then creation of B-H bond is the key issue to increase conversion yield of AB.

Borazino-Doped Polyphenylenes.

The divergent synthesis of two series of borazino-doped polyphenylenes, in which one or more aryl units are replaced by borazine rings, is reported for the first time, taking advantage of the decarbonylative [4 + 2] Diels-Alder cycloaddition reaction between ethynyl and tetraphenylcyclopentadienone derivatives. Because of the possibility of functionalizing the borazine core with different groups on the aryl substituents at the N and B atoms of the borazino core, we have prepared borazino-doped polyphenylenes featuring different doping dosages and orientations. To achieve this, two molecular modules were prepared: a core and a branching unit. Depending on the chemical natures of the central aromatic module and the reactive group, each covalent combination of the modules yields one exclusive doping pattern. By means of this approach, three- and hexa-branched hybrid polyphenylenes featuring controlled orientations and dosages of the doping B3N3 rings have been prepared. Detailed photophysical investigations showed that as the doping dosage is increased, the strong luminescent signal is progressively reduced. This suggests that the presence of the B3N3 rings engages additional deactivation pathways, possibly involving excited states with an increasing charge-separated character that are restricted in the full-carbon analogues. Notably, a strong effect of the orientational doping on the fluorescence quantum yield was observed for those hybrid polyphenylene structures featuring low doping dosages. Finally, we showed that Cu-catalyzed 1,3-dipolar cycloaddition is also chemically compatible with the BN core, further endorsing the inorganic benzene as a versatile aromatic scaffold for engineering of molecular materials with tailored and exploitable optoelectronic properties.

High char yield novolac modified by Si-B-N-C precursor: Thermal stability and structural evolution

In this contribution, novolac modified by CSEB ceramic precursor (B,B,B-tris[(chlorodimethylsilyl)-ethane]borazine, CSEB) was synthesized successfully. The corresponding molecular structure, chemical state and thermal property were characterized by FT-IR, Raman spectra, XPS, NMR and TGA. Meanwhile, DTA/TG/MS test was also performed to track the weight loss and gas evolution of modified novolac during the thermal degradation. CSEB could obviously improve the thermal decomposition temperature and the char yield of novolac. The maximum decomposition rate temperature is increased up to 575.2 °C. The char yield is increased to 75.5% at 800 °C, 72.6% at 1000 °C and 68.7% at 1200 °C, respectively. The improvement of the thermal stability of modified novolac could be mainly attributed to the incorporation of six-membered borazine ring (B3N3), elements of Si, B and N. The B3N3 ring remains stable at 1400 °C. And fixed structure Si-Ox was formed during heat treatment. Moreover, CSEB also promote the graphitization.

Structures and Infrared Spectroscopy of Metal Cation-Borazine Complexes

Borazine (B3N3H6) is known as ‘inorganic benzene’ because of a planar B3N3 ring with equivalent B-N distance. The lone pair from N in the ring delocalize to the adjacent p-orbital of B which leads to a conjugated system. Even though metal-benzene complexes have been studied extensively as models for cation- π interactions and organometallic bonding, similar systems with borazine is relatively scarce. Here, we present a density functional study on metal cation-borazine complexes focusing on geometric and electronic structures and their effects on infrared spectra. We have chosen Al, V, Mn, and Zn cations with various d-configurations which provide models for study donor-acceptor complexes. Among these four metal complexes, Al + and Mn + prefer to bind to π-cloud on top of the borazine ring. On the other hand, V + and Zn + bind to B and N, respectively. Infrared spectra of these complexes show four major bands: N-H-, B-H stretches and B-N-B ring and scissoring modes. Interactions of Al and Mn barely shift these band positions in the respective complexes as compared to those in isolated borazine, because of less cation-π interactions. On the other hand, V + and Zn + significantly perturb the borazine ring resulting shifts in

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.

Synthesis and Structure of per‐Methylated B6N7‐Azaboraphenalene

AbstractTricyclic nonamethyl‐B6N7‐phenalene, Me9B6N7 (1) was prepared from N(BCl2)3 and MeB(NHMe2)2 in the presence of NEt3. Its B3N3 rings are twisted against each other by 8 and 11° and the B–N bond lengths vary from 1.412(9) to 1.482(9) Å. The tricyclic ring is rather stable as shown by its mass spectrum, which is dominated by the loss of Me groups as well as by the formation of doubly charged fragments of the tricycle. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis and properties of N3 and CN delivery compounds and related precursors for nitride and ceramic fabrication

AbstractThe simple azido and cyano compounds Cl2AsN3, Br2AsN3, (C6H5)SiH2N3, (C6H5)SiH2CN and p‐(tolyl)SiH2CN have been prepared for the first time by metathesis reactions involving the corresponding halides and NaN3, LiN3 and LiCN. These compounds represent a highly reactive and efficient family of delivery reagents for the preparation of N3 and CN molecular precursors to bulk ceramics and nitride thin films. They are isolated as low volatility liquids and characterized by spectroscopic methods and chemical analysis. Ab initio simulations were used to elucidate the structural and vibrational properties of the simpler, fully inorganic Cl2AsN3 and Br2AsN3 species. This theoretical treatment was extended to include the hypothetical H2AsN3 and HClAsN3 derivatives which are particularly desirable as single‐source low‐temperature AsN sources for the formation of highly sought after, metastable GaAs1−xNx materials for solar cell applications. The practical utility of the title molecules is also demonstrated by synthesizing several representative compounds of B, Be, Ga and Al, which are of interest for the development of open frameworks, optoelectronic nitrides and refractory BCN hybrids. The cyanide derivatives (C6H5)SiH2CN and p‐(tolyl)SiH2CN react readily with Be and B halides to yield crystalline Be(CN)2 and amorphous BCN. The latter is crystallized upon heating to form graphite‐like polymorphs with homogeneous nanoscale morphologies. The azide derivatives Cl2AsN3, Br2AsN3 and (C6H5)SiH2N3 react readily with GaBr3, GaCl3 and BBr3 to produce high yields of the previously reported Br2GaN3, Cl2GaN3 and Br2BN3, respectively. The latter is shown to possess a trimeric molecular structure in which the α‐nitrogen of the azide group bridges the boron atoms to form cyclohexane‐like B3N3 rings. Copyright © 2008 John Wiley & Sons, Ltd.

2,4,6-Trichloro-1,3,5-trimethylborazine

The title compound, (CH3NBCl)3 or C3H9B3Cl3N3, is the first crystallographically characterized trialkyltrichloroborazine derivative. It crystallizes with two independent molecules in the asymmetric unit. The B3N3 rings are essentially planar, with B—N distances ranging from 1.428 (5) to 1.449 (4) Å, and with B—N—B and N—B—N angles in the ranges 118.4 (3)–119.4 (3) and 120.7 (3)–121.8 (3)°, respectively. The two independent molecules are staggered parallel along [x, 0, 0] and [x, {1 \over 2}, {1 \over 2}], most probably due to the formation of weak intermolecular C—H...Cl hydrogen bonds.

The Structural Chemistry of N‐Monolithium Borazines

AbstractTrimethylborazine (Me3B3N3H3, 1) reacts with RLi (R = nBu, tBu) in hexane solution by alkyl group exchange to give a mixture of borazines Me3–nRnB3N3H3. In contrast, deprotonation of 1 to Me3B3N3H2Li (2) occurs upon treatment with MeLi in diethyl ether solution or RLi (R = nBu, tBu) complexed with tetramethylethylenediamine (TMEDA), pentamethyldiethylentriamine (PMDTA), or trimethylhexahydrotriazine (TMTA) in hexane solution, to give solvates of 2. [(Me3B3N3H2)Li(OEt2)] (2a), [(Me3B3N3H2)Li(tmta)] (2c), and [(Me3B3N3H2Li)4(tmeda)3] (2b) contain dimeric units of 2. In the case of 2b two of these dimers are bridged by one tmeda molecule, while the other two are coordinated to a lithium atom of one of its dimeric units, respectively. This molecule therefore contains tri‐ and tetracoordinated Li atoms. In contrast, [(Me3B3N3H2)Li(pmdta)] (2c) is monomeric. The N‐lithiation leads to a distortion of the planar B3N3 ring system: the B–N bonds at the metallated N atoms are short, the next opposite B–N pair is the longest, followed by a shorter B–N bond involving the B atom in the para position. However, all B–N bonds are longer than in the parent compound 1. Reaction of tBu3B3N3H3 (3) with tBuLi in the presence of triisopropylhexahydrotriazine (TIPTA) in hexane leads to the salt [(tipta)2Li][tBu4B3N3H3] (4), while deprotonation occurs with tBuLi(tmta) to give monomeric [(tBu3B3N3H2)Li(tmta)] (5) after refluxing the reaction mixture. Similarly, (Me2N)3B3N3H3 (6) can be deprotonated with RLi in the presence of TMTA to give monomeric [{(Me2N)3B3N3H2}Li(tmta)] (7b). The N‐lithiation has almost no influence on the shielding of the boron nucleus of the borazine nuecleus. Attempts to obtain di‐ and trilithiated 1 as pure compounds failed: alkyl group exchange and borate formation as well as destruction of the borazine ring were detected by NMR spectroscopy. However, treatment of these reaction mixtures with MeBr gave Me3B3N3NH3–nMen (n = 0–3). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

An asymmetrically substituted borazine

The B3N3 ring in the title compound, 1,3,5-tri-tert-butyl-2,4-difluoro-6-phenylcyclotriborazane, [PhF2B3N3(t)Bu3] or C18H32B3F2N3, an asymmetrically substituted borazine, is distorted from planarity. The molecule resides on a twofold axis. The N atoms of the N-B(Ph)-N group lie on opposite sides of the least-squares plane formed by the four remaining ring atoms, due to steric accommodation of the tert-butyl groups, a conformation not previously observed for a borazine. The B-N bond lengths are in the range 1.4283 (14)-1.4493 (12) A, due to the F substituents residing on two of the B atoms, which also produce a large deviation from 120 degrees in one of the B-N-B angles [ca 113.6 (1) degrees]. The phenyl group is twisted with respect to the B3N3 ring, the interplanar angle being 62.87 (5) degrees.

High‐resolution 15N solid‐state NMR investigations on borazine‐based precursors

AbstractReference compounds based on borazine units and polyborylborazines have been characterized by 15N solid‐state NMR. The various nitrogen sites (B3N, B2NH, B2NX (X = H, Me, iPr), BN(H)X and BNX2 (X = Me, iPr) have been discriminated according to their cross‐polarization behaviour and chemical shift values, which range from −265 to −350 ppm. This has permitted the elucidation of the polymerization mechanism associated with the polycondensation of two borazine‐based derivatives. In particular, this technique appears to be a powerful investigation tool for finding whether the B3N3 rings are linked through three‐atom NBN aminoboryl bridges or connected by direct BN bonds. Copyright © 2004 John Wiley & Sons, Ltd.

Boron Nitride Fibers Prepared from Symmetric and Asymmetric Alkylaminoborazines

The thermolysis of 2,4,6-[(CH3)2N]3B3N3H3 (1), 2,4-[(CH3)2N]2-6-(CH3HN)B3N3H3 (2), and 2-[(CH3)2N]-4,6-(CH3HN)2B3-N3H3 (3) led to polyborazines 4, 5, and 6 respectively. The polymers display direct B–N bonds between borazinic B3N3 rings and, in addition, a proportion of –N(CH3)– bridges for 5 and 6, as clearly underlined by 13C NMR spectroscopy. Melt-spinning of these three polymeric precursors exemplified that their ease of processing increases in the order 4 < 5 < 6. Nevertheless, polyborazine filaments could be prepared from each of them and a subsequent thermal treatment up to 1800 °C resulted in the formation of crystalline hexagonal boron nitride fibers, which were characterized by X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images showed that the ceramic fibers are circular and dense without major defects. The mechanical properties for 4-derived fibers could not be measured because of their brittleness, whereas measurements on 5- and 6-derived fibers gave tensile strength σR = 0.51 GPa, Young’s modulus E = 67 GPa, and σR = 0.69 GPa, E = 170 GPa, respectively. The improvement in mechanical properties for ceramic fibers prepared respectively from 4, 5, and 6 could be explained to a large extent by the improvement of the processing properties of the preceramic polymers. This evolution could be related to the increased ratio of bridging –N(CH3)– groups between the B3N3 rings within the polymers 4, 5, and 6 and therefore to the functionalities of the starting monomers 1, 2, and 3.

Synthesis and characterization of poly(aminoborane) as a new boron nitride precursor

During the solution reaction of NaBH4/(NH4)2SO4 in tetraglyme to form borazine, polymeric aminoborane (NH2BH2)x has been isolated as a white powder. The powder was characterized by thermal gravimetric analysis/differential scanning calorimetry, infrared and mass spectroscopies, and powder X-ray diffraction. Solid-state 15N and 11B nuclear magnetic resonance firmly proved that the chain-like poly(aminoborane) evolved a partially condensed B3N3 ring structure by dehydrogenative condensation between chains at 200 °C. Pyrolysis of the polymer in a nitrogen stream up to 1400 °C led to a 75% yield of hexagonal boron nitride with an interlayer spacing of 3.37 Å. Copyright © 1999 John Wiley & Sons, Ltd.

Synthesis and characterization of poly(aminoborane) as a new boron nitride precursor

During the solution reaction of NaBH4/(NH4)2SO4 in tetraglyme to form borazine, polymeric aminoborane (NH2BH2)x has been isolated as a white powder. The powder was characterized by thermal gravimetric analysis/differential scanning calorimetry, infrared and mass spectroscopies, and powder X-ray diffraction. Solid-state 15N and 11B nuclear magnetic resonance firmly proved that the chain-like poly(aminoborane) evolved a partially condensed B3N3 ring structure by dehydrogenative condensation between chains at 200 °C. Pyrolysis of the polymer in a nitrogen stream up to 1400 °C led to a 75% yield of hexagonal boron nitride with an interlayer spacing of 3.37 Å. Copyright © 1999 John Wiley & Sons, Ltd.

Synthesis of Mono-B-alkylcyclotriborazanes. Structural Characterization of 2-(PhC(2)H(4))B(3)N(3)H(11).

The new mono-B-alkylcyclotriborazanes 2-(PhC2H4)B3N3H11 and 2-(C2H5)B3N3H11 have been synthesized by reaction of the mono-B-alkylborazines 2-(PhC2H4)B3N3H5 and 2-(C2H5)B3N3H5 with HCl, followed by reduction of the 2-RB3N3H5·3HCl intermediates with NaBH4. A structural determination of 2-(PhC2H4)B3N3H11 confirmed that the B3N3 ring adopts a chair conformation with the alkyl group attached to B2 in an equatorial position.