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Detection of the Elusive Triazane Molecule (N3H5) in the Gas Phase

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DOI:10.1002/cphc.201500560 Communications Detection of the Elusive Triazane Molecule (N3H5)inthe Gas Phase MarkoFçrstel,[a] PavloMaksyutenko,[a] BrantM.Jones,[a] Bing-Jian Sun,[b] Shih-Hua Chen,[b] Agnes. H.-H. Chang,*[b] and Ralf I. Kaiser*[a] We report the detection of triazane (N3H5)inthe gas phase. Tri- ful and only potential decompositionproducts of triazane azane is ahigher order nitrogen hydride of ammonia (NH3) (N3H5)—diazane (HNNH) and ammonia (NH3)—could be sam- [1c] [1d] and hydrazine (N2H4)offundamentalimportance for the un- pled. Finally,Fuji et al. made an effort to detect free tria- derstanding of the stability of single-bonded chains of nitro- zane in the microwave discharge of hydrazine, but only the + gen atomsand apotentialkey intermediate in hydrogen–nitro- lithium salt of triazane (LiN3H5 )and the triazane cation + gen chemistry. The experimental resultsalongwith electronic- (N3H5 )could be identified. Therefore, whether free triazane structurecalculations reveal that triazane presentsastable (N3H5)can surviveprompt dissociation in the gas phase has re- molecule with anitrogen–nitrogen bond length that is afew mained an unanswered question. This lack of experimental evi- picometers shorter than that of hydrazineand has alifetime dence on the stability of triazane has triggered substantial exceeding 6 2 msatasublimation temperature of 170 K. Tria- computational efforts.[1a,b] An evaluation of the thermodynamic Æ zane was synthesized throughirradiation of ammonia ice with stability, accounting for hydrogen bonding as well as hyper- energetic electrons and was detected in the gas phase upon conjugation effects, reveals three triazane conformers with C1 sublimation of the ice through soft vacuum ultraviolet (VUV) and Cs symmetries, which range in stability within 24 kJ 1 [1a,b] photoionization coupled with areflectron-time-of-flight mass molÀ . Accounting for potentialdecomposition pathways, spectrometer.Isotopic substitutionexperiments exploiting such as ammonia and diazene elimination, Schlegel and [1b] [D3]-ammonia ice confirmed the identificationthrough the de- Skancke concludedthat “there appears to be no low energy tection of its fully deuterated counterpart[D5]-triazane (N3D5). channels for the unimolecular decomposition of triazane” and that triazane represents a“promising candidate(s) for synthe- sis.” The triazane molecule (N3H5)has been long postulated to be Here, we report the experimental detection of the hitherto akey transientspecies in nitrogen–hydrogen chemistry and elusivetriazane molecule (N3H5)inthe gas phase. Our experi- has received considerable interest from the viewpoint of chem- ments are combined with ab initio electronic-structure calcula- ical bonding theory and as apromising high-energymaterial.[1] tions to verify the stability of triazane in the gas phase. The ex- Unlike carbon chemistry,the nitrogen–nitrogen single bond is periments were carriedout in an ultrahigh vacuum (UHV) sur- 11 [3] destabilized by the nonbonding electron pairs of the neighbor- face science machine operated at apressure of a3x10À torr. ing nitrogen atoms, resulting in significantly weaker nitrogen– Amorphous ices of ammonia (NH3)and [D3]-ammonia (ND3) 1 nitrogen single bonds(157–168kJmolÀ )compared to their were prepared in separate experiments with thicknesses of 1 carbon–carbon counterparts (345–355 kJmolÀ ). Consequently, 500 50 nm at 5.5 0.2 K. Nonequilibrium chemistry was in- Æ Æ single-bonded hydrides of nitrogen are extremelyrare and duced by irradiating these ices with energetic electrons (5 keV) only the methane (CH4)and ethane (C2H6)analoguesofnitro- for one hour at an averaged dose of 1.9 0.2 eV per molecule. Æ 1 gen—ammonia (NH3)and hydrazine (N2H4)—have been isolat- After irradiation, the ices were heated at arate of 0.5 KminÀ ed to date. The next higher homologue, triazane, wasreported (temperature-programmed desorption;TPD). During the TPD crystallographically in azeolite, where it was stabilized by com- process, the subliming neutralmolecules were first ionized 2+ [2] plexion to silver ions as Ag2(N3H5)3 . Attempts to isolate tria- through single vacuum ultraviolet (VUV) photon ionization at zane from triazanium sulfite salts, (N3H6)2SO3,were unsuccess- 10.49 eV,then mass resolved in areflectron time-of-flight mass spectrometer (Re-TOF), and eventually identified by their arrival [a] Dr.M.Fçrstel, Dr.P.Maksyutenko, Dr.B.M.Jones, Prof. Dr.R.I.Kaiser times through amultichannel plate (see the Supporting Department of Chemistry Information). University of Hawaii The mass spectra of the subliming molecules released from 2545 McCarthy Mall Honolulu,HI96822-2275 (USA) the irradiated ammonia ices are shown as afunction of tem- E-mail:[email protected] peratureinFigure 1. These spectra are dominated by the am- + [b] Dr.B.-J. Sun, Dr.S.-H. Chen, Prof. Dr.A.H.-H. Chang monia and[D3]-ammonia parentions at m/z=17 [NH3 ;ioniza- Department of Chemistry tion energy (IE)=10.07 0.02 eV] in the irradiated ammonia Æ NationalDong Hwa University ices shiftedby3to m/z=20 (ND +)inthe exposed [D ]-ammo- Shou-Feng,Hualien, 974(Taiwan) 3 3 E-mail:[email protected] nia samples (Figure 2). As the temperature rises, hydrazine Supporting Information for this article is available on the WWW under (N2H4)together with its deuterated counterpart (N2D4)are ob- http://dx.doi.org/10.1002/cphc.201500560. servable through their parent ions at m/z= 32 and 36 (IE= ChemPhysChem 2015, 16,3139 –3142 3139 2015 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Communications ated, closed-shell nitrogen hydride. The molecularions at + + m/z=47 (N3H5 )and 52 (N3D5 )are stable in the ReTOF de- picting–based on the time-of-flight—life times of at least 30 Æ 1 ms; the stabilityofthe molecular ion is consistent with the study of Fuji et al. that identified the triazane cation in the mi- crowavedischargeofhydrazine. Finally,wewould like to out- line that the second ion peak and the shoulder of the TPD at + + m/z=48 (N3D3 )and 45 (N3H3 ), respectively,emerging at about 160 Kmight origin from N3D3/N3H3 isomers triazene (H2NNNH)and/or cyclotriazane (c-N3H3)togetherwith their deuterated counterparts. It is important to stress that we also conducted control ex- Figure 1. Reflectron time-of-flight (ReTOF) mass spectra as afunction of the periments, that is, experiments under identical conditions, but temperature of the newly formed products subliming into the gas phase from the irradiated ammonia ice measured at 10.49 eV.The signalofthe withoutirradiating the ices with energetic electrons. In these most abundant species at 17 (ammonia) was truncated to allow for abetter control studies, only ion signals derived from ammonia and representation of the data. [D3]-ammonia were observable.This demonstrates that the abovementioned products and the triazane molecule in partic- ular are aresult of the radiolysis of the ammonia ices, and not an artifact from the photolysis and/or ion–molecule reactions of the subliming ammonia. Therefore, our data provide com- pelling evidence that amolecule with the molecular formulae N3H5 (ammonia ice) and N3D5 ([D3]-ammonia ice) have been formed in the ices upon exposure to energetic electrons;these specieswere released into the gasphase upon sublimation and then ionizedbysingle-photon ionization. The calculated adiabatic IE of triazane was computed to be 7.7 0.1 eV,which Æ is well below the energy of the vacuum ultraviolet photon of 10.49 eV exploited to ionize the subliming molecules (see the Supporting Information).Considering the root-mean-square 1 Figure 2. Temperature desorption profiles of key species subliming from the velocityof310 msÀ of atriazane molecule subliming at 170 K irradiated ammonia (left) and [D3]-ammonia ices (right). Statistical error bars and the distance betweenthe ice and the photoionization are included in Panels (A)and (B) for the newly identified triazanemolecule. laser of 2mm, we determined alifetimeofthe subliming tria- Traces in blue show the signal from the irradiated sample and traces in red zane and [D5]-triazane molecules of at least 6 2and 7 2 ms, are those measured for the nonirradiated sample. Æ Æ respectively,and possibly much longer. 8.10 0.15 eV), respectively,asthey are released into the gas Æ phase with ion counts peakingat160 K. With increasing tem- + perature, we also observedsignal at m/z=30 (N2H2 ), 45 + + (N3H3 ), and 47 (N3H5 )along with their deuteratedcounter- + + + parts at m/z=32 (N2D2 ), 48 (N3D3 ), and 52 (N3D5 )peaking at about 170 K. Signals at m/z= 30 and45originate from ion- ized N H (IE=9.8 0.1 eV) and N H (IE=9.6 0.1 eV), respec- 2 2 Æ 3 3 Æ tively.Nomasses higher than 47 and 52 were observed for the irradiated ammonia and [D3]-ammonia ices, respectively.Itis important to stress that ionsignals depicting identical TPD profiles indicate that fragmentation of the molecules with the + highest mass may occur.Here, signals at m/z=17 (NH3 ), 30 + + (N2H2 ), and 45 (N3H3 ), the TPD profiles of which peak at + about 170 K, match the TPD profileofm/z= 47 (N3H5 ), thus indicating that the lower masses are fragments from amolecule that contains nitrogen andhydrogen atoms with amolecular weightof47, that is, triazane(N3H5). In case of [D3]-ammonia + ices, the fragment masses are shiftedtom/z=20 (ND3 ), 32 + + (N2D2 ), and 48 (N3D3 ), which, in turn, are fragments from [D ]-triazane (N D )upon photoionization. Note that m/z= 47 Figure 3. Structures of three conformersoftriazane, I–III,together with their 5 3 5 computed decomposition pathways of triazane. All energies are given in + + 1 (N3H5 )and 52 (N3D5 )cannot originate from higher masses, kJ molÀ .The molecular structures of the reactants,intermediates, products, as N3H5/N3D5 resembles the heaviest allowable fully hydrogen- and transitionstates are shown in Figure 4. ChemPhysChem 2015, 16,3139 –3142 www.chemphyschem.org 3140 2015 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Communications Figure 4. Structures of reactant conformers (I–III), the intermediate (INT1), products, and transition states (TS1–TS4); bond lengths and angles are definedin pm and degrees, respectively.Also shown is the structure of the triazane ion.
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    Chapter 9 Hydrogen Diborane, B2 H6• is the simplest member of a large class of compounds, the electron-deficient boron hydrid Like all boron hydrides, it has a positive standard free energy of formation, and so cannot be prepared direct from boron and hydrogen. The bridge B-H bonds are longer and weaker than the tenninal B-H bonds (13: vs. 1.19 A). 89.1 Reactions of hydrogen compounds? (a) Ca(s) + H2Cg) ~ CaH2Cs). This is the reaction of an active s-me: with hydrogen, which is the way that saline metal hydrides are prepared. (b) NH3(g) + BF)(g) ~ H)N-BF)(g). This is the reaction of a Lewis base and a Lewis acid. The product I Lewis acid-base complex. (c) LiOH(s) + H2(g) ~ NR. Although dihydrogen can behave as an oxidant (e.g., with Li to form LiH) or reductant (e.g., with O2 to form H20), it does not behave as a Br0nsted or Lewis acid or base. It does not r with strong bases, like LiOH, or with strong acids. 89.2 A procedure for making Et3MeSn? A possible procedure is as follows: ~ 2Et)SnH + 2Na 2Na+Et3Sn- + H2 Ja'Et3Sn- + CH3Br ~ Et3MeSn + NaBr 9.1 Where does Hydrogen fit in the periodic chart? (a) Hydrogen in group 1? Hydrogen has one vale electron like the group 1 metals and is stable as W, especially in aqueous media. The other group 1 m have one valence electron and are quite stable as ~ cations in solution and in the solid state as simple 1 salts.
  • Large Intermediates in Hydrazine Decomposition: a Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces

    Large Intermediates in Hydrazine Decomposition: a Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces

    Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Grinberg Dana, Alon et al. "Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N₃H₅ and N₄H₆ Potential Energy Surfaces." Journal of Physical Chemistry A 123, 22 (May 2019): 4679-4692 © 2019 American Chemical Society As Published http://dx.doi.org/10.1021/acs.jpca.9b02217 Publisher American Chemical Society (ACS) Version Author's final manuscript Citable link https://hdl.handle.net/1721.1/124015 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The Journal of Physical Chemistry This document is confidential and is proprietary to the American Chemical Society and its authors. Do not copy or disclose without written permission. If you have received this item in error, notify the sender and delete all copies. Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N3H5 and N4H6 Potential Energy Surfaces Journal: The Journal of Physical Chemistry Manuscript ID jp-2019-02217p.R1 Manuscript Type: Article Date Submitted by the n/a Author: Complete List of Authors: Grinberg Dana, Alon; Massachusetts Institute of Technology, Chemical Engineering Moore, Kevin; Argonne National Laboratory, Gas Phase Chemical Dynamics Jasper, Ahren; Argonne National Laboratory, Gas Phase Chemical Dynamics Green, William; Massachusetts Institute of Technology, Chemical Engineering ACS Paragon Plus Environment Page 1 of 60 The Journal of Physical Chemistry 1 2 3 4 5 Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the 6 7 N3H5 and N4H6 Potential Energy Surfaces 8 9 1 2 2 1 10 Alon Grinberg Dana , Kevin B.