Tetranitrogen is a neutrally charged polynitrogen

allotrope Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...

of the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

and consists of four

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

atoms. The tetranitrogen cation is the positively charged ion, , which is more stable than the neutral tetranitrogen molecule and is thus more studied. Tetranitrogen anions ( and ) have also been reported. Laniel, D., Winkler, B., Koemets, E. et al. Synthesis of magnesium-nitrogen salts of polynitrogen anions. Nat Commun 10, 4515 (2019). https://doi.org/10.1038/s41467-019-12530-w

History

Polynitrogen compounds have been well known and characterized by

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...

s for many years. The commonplace molecular (

diatomic Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear mol ...

)

() was first isolated by

Daniel Rutherford Daniel Rutherford (3 November 1749 – 15 November 1819) was a Scottish physician, chemist and botanist who is known for the isolation of nitrogen in 1772. Life Rutherford was born on 3 November 1749, the son of Anne Mackay and Professor J ...

in 1772 and the

azide In chemistry, azide (, ) is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant ...

ion () was discovered by Theodor Curtius in 1890. Discoveries of other related nitrogenous allotypes during the twentieth century include the

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

molecule

pentazole Pentazole is an aromatic molecule consisting of a five-membered ring with all nitrogen atoms, one of which is bonded to a hydrogen atom. It has the molecular formula . Although strictly speaking a homocyclic, inorganic compound, pentazole has ...

and the

radical Radical (from Latin: ', root) may refer to: Politics and ideology Politics *Classical radicalism, the Radical Movement that began in late 18th century Britain and spread to continental Europe and Latin America in the 19th century *Radical politics ...

molecule . However, none of these complexes could be isolated or synthesized on a

macroscopic scale The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the opposite of microscopic. Overview When applied to physical phenom ...

like and azide; it was not until 1999 that a large scale synthesis was devised for a third nitrogen allotrope, the

pentazenium In chemistry, the pentazenium cation (also known as pentanitrogen) is a positively-charged polyatomic ion with the chemical formula and structure . Together with solid nitrogen polymers and the azide anion, it is one of only three poly-nitrogen ...

()

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

. This increased interest in polynitrogen compounds in the late twentieth century was due to the advance of

computational chemistry Computational chemistry is a branch of chemistry that uses computer simulations to assist in solving chemical problems. It uses methods of theoretical chemistry incorporated into computer programs to calculate the structures and properties of mol ...

which predicted that these types of molecules could be used as potential high-energy-density matter (HEDM) sources. The cation was first discovered in 1958 upon analysis of anomalous background peaks of

molecular weight A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

56+ and 42+ in the mass spectra of molecular nitrogen, which corresponded with formation of and , respectively. Explicit synthesis of was first carried out in 1984 by a similar mechanism of electron bombardment of .

Theoretical chemistry Theoretical chemistry is the branch of chemistry which develops theoretical generalizations that are part of the theoretical arsenal of modern chemistry: for example, the concepts of chemical bonding, chemical reaction, valence, the surface ...

predicted several possible synthesis mechanisms for including reaction of a neutral N atom with a radical, binding of two molecules in the excited state, and extrusion from

polycyclic compound In the field of organic chemistry, a polycyclic compound is an organic compound featuring several closed ring (chemistry), rings of atoms, primarily carbon. These ring substructures include cycloalkanes, aromaticity, aromatics, and other ring ...

s, none of which could be accomplished experimentally. However, in 2002 a method for synthesis of tetranitrogen was devised from the deionization of through neutralization-reionization

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...

(NRMS). In the synthesis, (which was first formed in the ionization chamber of the mass spectrometer) underwent two high energy collision events. During the first collision, contacted a target gas, , to yield a small percentage of neutral molecules. : + → + A deflecting

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

was used to remove any unreacted ions as well as the target

gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

, , and any additional unintended reaction products, leaving a stream of molecules. In order to affirm the synthesis and isolation of , this stream then underwent a second collision event, contacting a second target gas, , reforming the cation. : + → + The disappearance and reemergence of this "recovery peak" confirms the completion of both reactions, providing ample evidence for the synthesis of by this method. As the "flight time" between the two reactions, carried out in separate chambers of the mass spectrometer, was on the order of 1

μs A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, ...

, the molecule has a lifetime of at least this long.

Characteristics

Since its discovery, has not been well studied. It is a gas at room temperature (). It also has a lifetime in excess of 1 μs, though it is predicted to be characterized as

metastable In chemistry and physics, metastability is an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is onl ...

. Due to its instability, the N₄ molecule readily disassociates into two more-stable N₂ molecules. This process is very

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...

, releasing around 800 kJ mol⁻¹ of energy.

Ab initio ( ) is a Latin term meaning "from the beginning" and is derived from the Latin ("from") + , ablative singular of ("beginning"). Etymology , from Latin, literally "from the beginning", from ablative case of "entrance", "beginning", related t ...

calculations in the neutral molecular suggest that previously proposed rectangular or

tetrahedral In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

structures, analogous to

cyclobutadiene Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is ...

and

tetrahedrane Tetrahedrane is a hypothetical platonic hydrocarbon with chemical formula and a tetrahedral structure. The molecule would be subject to considerable angle strain and has not been synthesized . However, a number of derivatives have been prepa ...

, respectively, are not likely to be the most

thermodynamically stable In chemistry, chemical stability is the thermodynamic stability of a chemical system, in particular a chemical compound or a polymer. Colloquially, it may instead refer to kinetic persistence, the shelf-life of a metastable substance or system; th ...

. Instead, the

ground state The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state ...

is expected to be a bent or zig-zag linear chain of the four nitrogen atoms containing two

unpaired electron In chemistry, an unpaired electron is an electron that occupies an orbital of an atom singly, rather than as part of an electron pair. Each atomic orbital of an atom (specified by the three quantum numbers n, l and m) has a capacity to contai ...

s on one of the terminal nitrogen atoms—essentially an

azido In chemistry, azide (, ) is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant a ...

nitrene In chemistry, a nitrene or imene () is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and valence (chemistry)#monovalent, monovalent, so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded e ...

. The structure of has been predicted by theoretical experiments and confirmed by experimental techniques involving collisionally activated dissociation mass spectrometry (CADMS). This technique bombards -producing fragments which can then be analyzed by

tandem mass spectrometry Tandem mass spectrometry, also known as MS/MS or MS2, is a technique in instrumental analysis where two or more stages of analysis using one or more mass analyzer are performed with an additional reaction step in between these analyses to increa ...

. Based on the fragments observed, a structure was determined invlvolving two pairs of triple-bonded nitrogen atoms (two units) that are associated with each other with a longer, weaker bond.

Applications

Tetranitrogen and other similar polynitrogen compounds are predicted to be good candidates for use as high-energy-density matter (HEDM), high-energy fuel sources with small weight in comparison with traditional liquid- and fuel-cell-based energy sources. The N≡N

triple bond A triple bond in chemistry is a chemical bond between two atoms involving six Electron pair bond, bonding electrons instead of the usual two in a covalent bond, covalent single bond. Triple bonds are stronger than the equivalent covalent bond, sin ...

of is much stronger ( energy of formation of 229

kcal KCAL may refer to: * KCAL (AM), a radio station (1410 AM) licensed to Redlands, California, United States * KCAL-FM, a radio station (96.7 FM) licensed to Redlands, California, United States *KCAL-TV KCAL-TV (channel 9) is an independent tel ...

/ mol) than either an equivalent one and a half N=N

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

s (100 kcal/mol, i.e. 150 kcal/mol total) or an equivalent three N−N

single bond In chemistry, a single bond is a chemical bond between two atoms involving two valence electrons. That is, the atoms share one pair of electrons where the bond forms. Therefore, a single bond is a type of covalent bond. When shared, each of th ...

s (38.4 kcal/mol, i.e. 115 kcal/mol total). Due to this, polynitrogen molecules are expected to readily break down into harmless gas, in the process releasing large amounts of chemical energy. This is in contrast to

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

-containing compounds which have lower energies of formation for an equivalent number of single or double bonds than for a C≡C triple bond, allowing for the thermodynamically favorable formation of

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s. It is for this reason that the only allotropic form of nitrogen found in nature is molecular nitrogen () and why novel strategies of synthesizing polynitrogen allotropes in a cost-efficient manner are so highly sought after.

References

{{Reflist, refs= {{cite book , last=Rutherford , first=Daniel , authorlink=Daniel Rutherford , date=1772 , title=De aere fixo dicto, aut mephitico , trans-title=On air said to be fixed or mephitic , url=https://books.google.com/books?id=vLmenQEACAAJ , location=University of Edinburgh , publisher=Balfour & Smellie {{cite journal , last=Curtius , first=Theodor , date=1890 , title=Ueber Stickstoffwasserstoffsäure (Azoimid) N₃H , trans-title=On Hydrazoic Acid (Azoimide) N₃H , language=German , journal=Berichte der Deutschen Chemischen Gesellschaft , volume=23 , issue=2 , pages=3023–3033 , doi=10.1002/cber.189002302232 , url=https://zenodo.org/record/1425592 {{cite journal , title={{chem , N , 5 , +: A Novel Homoleptic Polynitrogen Ion as a High Energy Density Material, journal=Angewandte Chemie International Edition, issue=13–14, volume=38, pages=2004–2009, date=12 Jul 1999, doi=10.1002/(SICI)1521-3773(19990712)38:13/14<2004::AID-ANIE2004>3.0.CO;2-7, first1=Karl O., last1=Christe, first2=William W. , last2=Wilson , first3=Jeffrey A. , last3=Sheehy , first4=Jerry A. , last4=Boatz , pmid=34182671, doi-access=free {{cite journal , last1=Glukhovtsev , first1=Mikhail N. , last2=Jiao , first2=Haijun , last3=Schleyer , first3=Paul von Ragué , date=January 1996 , title=Besides N₂, What Is the Most Stable Molecule Composed Only of Nitrogen Atoms? , journal=Inorganic Chemistry , volume=35 , issue=24 , pages=7124–7133 , doi=10.1021/ic9606237 , pmid=11666896 {{cite journal , last1=Cacace , first1=F. , last2=de Petris , first2=G. , last3=Troiani , first3=A. , date=18 January 2002 , title=Experimental Detection of Tetranitrogen , journal=Science , volume=295 , issue=5554 , pages=480–481 , doi=10.1126/science.1067681 , pmid=11799238 , bibcode=2002Sci...295..480C , s2cid=35745247 {{cite journal , last1=Zarko , first1=V. E. , date=2010 , title=Searching for ways to create energetic materials based on polynitrogen compounds (review) , journal=Combustion, Explosion, and Shock Waves , volume=46 , issue=22 , pages=121–131 , doi=10.1007/s10573-010-0020-x , bibcode=2010CESW...46..121Z , s2cid=95184003 {{cite journal , last1=Nguyen , first1=Minh Tho , date=September 2003 , title=Polynitrogen compounds: 1. Structure and stability of N₄ and N₅ systems , journal=Coordination Chemistry Reviews , volume=244 , issue=1–2 , pages=93–113 , doi=10.1016/S0010-8545(03)00101-2 {{cite journal , last1=Junk , first1=Gregor , date=1 June 1958 , title=The Presence of {{chem , N , 3 , + and {{chem, N, 4, + in the Mass Spectra of Molecular Nitrogen , journal=Journal of the American Chemical Society , volume=80 , issue=11 , pages=2908–2909 , doi=10.1021/ja01544a085 {{cite journal, last1=Stephan, first1=K., last2=Märk, first2=T. D., last3=Futrell, first3=J. H., last4=Helm, first4=H., title=Electron impact ionization of (N₂)₂: Appearance energies of N⁺
₃ and N⁺
₃, journal=Journal of Chemical Physics, issue=80, page=3185, date=1 April 1984, publication-date=31 August 1998, doi=10.1063/1.447144, publisher=

American Institute of Physics The American Institute of Physics (AIP) promotes science and the profession of physics, publishes physics journals, and produces publications for scientific and engineering societies. The AIP is made up of various member societies. Its corpora ...

, as cited in {{cite journal , last1=Tosi , first1=P. , last2=Lu , first2=W. Y. , last3=Bassi , first3=D. , last4=Tarroni , first4=R. , date=1 February 2001 , title=The reaction {{chem , N , 2 , + + {{chem, N, 2 → {{chem, N, 3, + + N from thermal to 25 eV , journal=Journal of Chemical Physics , volume=114 , issue=5 , pages=2149–2153 , doi=10.1063/1.1336808 Allotropes of nitrogen

History

Characteristics

Applications

See also

References