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 In chemistry, 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, ...

and consists of four

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

atoms. The tetranitrogen cation is the positively charged ion, , which is more stable than the neutral tetranitrogen molecule and is thus more studied.

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 scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

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. Ot ...

)

() was first isolated by

Daniel Rutherford Daniel Rutherford (3 November 1749 – 15 December 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 John ...

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 applic ...

ion () was discovered by

Theodor Curtius ''Geheimrat'' Julius Wilhelm Theodor Curtius (27 May 1857 – 8 February 1928) was professor of Chemistry at Heidelberg University and elsewhere. He published the Curtius rearrangement in 1890/1894 and also discovered diazoacetic acid, hydra ...

in 1890. Discoveries of other related nitrogenous allotypes during the

twentieth century The 20th (twentieth) century began on January 1, 1901 (1901, MCMI), and ended on December 31, 2000 (2000, MM). The 20th century was dominated by significant events that defined the modern era: Spanish flu, Spanish flu pandemic, World War I and ...

include the

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

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 may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

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 phenomena an ...

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 simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into computer programs, to calculate the structures and properties of m ...

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 held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

56+ and 42+ in the

mass spectra A mass spectrum is a histogram plot of intensity vs. ''mass-to-charge ratio'' (''m/z'') in a chemical sample, usually acquired using an instrument called a ''mass spectrometer''. Not all mass spectra of a given substance are the same; for example ...

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 o ...

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 rings of atoms, primarily carbon. These ring substructures include cycloalkanes, aromatics, and other ring types. They come in sizes of t ...

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 use ...

(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 air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

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

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

, , 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. Because the "flight time" between the two reactions, carried out in separate chambers of the mass spectrometer, was on the order of 1 μs, 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 denotes an intermediate Energy level, energetic state within a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slope is a simple example of me ...

. 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 ''Ab initio'' ( ) is a Latin term meaning "from the beginning" and is derived from the Latin ''ab'' ("from") + ''initio'', ablative singular of ''initium'' ("beginning"). Etymology Circa 1600, from Latin, literally "from the beginning", from ab ...

calculations in the neutral molecular suggest that previously proposed rectangular or

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...

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 as of 2021. However, a number of derivatives have be ...

, respectively, are not likely to be the most

thermodynamically stable In chemistry, chemical stability is the thermodynamic stability of a chemical system. Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibriu ...

. 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 contain ...

s on one of the terminal nitrogen atoms—essentially an azido-

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

. 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 mass analyzers are coupled together using an additional reaction step to increase their abilities to analyse chemical samples. A comm ...

. 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 A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...

-based energy sources. The N≡N

triple bond A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order o ...

of is much stronger ( energy of formation of 229

kcal The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of o ...

/ 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). Because of 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 with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

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 (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

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 , 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