Nav: Home

Going against the grain -- nitrogen turns out to be hypersociable!

November 30, 2016

Going against the grain - nitrogen turns out to be hypersociable!

Nitrogen is everywhere: even in the air there is four times as much of it as oxygen. However, it is reluctant to form chemical bonds, especially with more than four atoms. Chemists from Warsaw predict, however, that contrary to the rules of typical chemistry, in appropriately selected conditions there may be a nitrogen that nobody has ever seen: one capable of forming up to six chemical bonds.

Nobody expected this. Computer simulations suggest that nitrogen, a very well-known element, with a reputation for being reluctant to react could, at a high enough pressure, break the chemical rules and become extremely gregarious: a single atom would then be able to form even six chemical bonds. This surprising discovery has been made by researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw and the New Technology Centre at the University of Warsaw (CeNT UW), funded by grants from the Polish National Science Centre.

Chemists have long known that nitrogen may occasionally have a valency of five, which means that it is potentially able to form bonds with five other atoms. Another element with similar properties is phosphorus, which is adjacent to nitrogen in the periodic table.

"Nitrogen, however, behaves differently to phosphorus: in practice, it forms five bonds with at most four other atoms, and more usually with three, as in the popular nitric acid HNO3. We decided to investigate, using the computer, the possibility of obtaining a compound in which pentavalent nitrogen would combine with five neighbours by covalent interactions - chemical bonds. We analyzed thousands of crystal structures of nitrogen compounds with fluorine arising at high pressures. We were hoping to see some structures containing nitrogen pentafluoride NF5 particles. We were completely unprepared for the fact that in one of the crystals we ran into ions with the formula NF6- in which the nitrogen atom bonds with as many as six fluorine atoms," says Dr. Patryk Zaleski-Ejgierd (IPC PAS).

Dr Dominik Kurzydlowski (CeNT UW), co-author of the publication in the journal Scientific Reports, explains the essence of the discovery as follows: "Two electrons are typically required for the formation of a single covalent bond. The problem with nitrogen lies in the fact that when creating various compounds it 'trades' electrons so as to always be surrounded by eight of them. This constrains the total number of atoms bonded to nitrogen to no more than four. We were the first to find a stable crystal in which nitrogen breaks the octet rule, i.e. the requirement to possess exactly eight electrons, and forms bonds involving a total of up to twelve electrons."

Compounds in which an element breaks the octet rule octet are called hypervalent. Many elements can form hypervalent compounds, including phosphorus, sulphur and various metals. This phenomenon is advantageous because it significantly widens the number of possible compounds the element can form. For example, if it were not for hypervalency, sulphur would not form sulphuric acid and phosphorus could not be one of the building blocks of DNA.

The calculations and simulations associated with the search for hypervalent nitrogen were carried out at the IPC PAS using density functional theory, that is, the method normally used in solid state calculations. However, the discovery's authors used one of the more advanced embodiments of this theory, the hybrid functional. It makes it possible to describe chemical bonds very accurately, but it takes much longer to perform the calculations.

"The compounds we tested, as well as the conditions under which these compounds were formed, were very exotic. The accuracy of the calculations was therefore our absolute priority which is why we decided to use the hybrid functional for the calculations," says Dr. Kurzydlowski and stresses that carrying out the simulation within a reasonable timeframe was made possible thanks to cooperation with the Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw.

A thorough analysis of the results of computer simulation allowed the researchers to identify the unique crystal structure that with an increase in pressure at some point automatically ionizes in a very particular way. A reorganization takes place during which the molecular crystal, originally formed of a mixture of gases NF3 and F2, transforms into a complex ionic crystal constructed of NF4-, NF2+ and... NF6- ions. (It should be mentioned here that despite the exotic name, ionic crystals are common in nature. They include many minerals, among others popular rock salt, whose crystal structure is formed of sodium cations Na+ and chloride anions Cl-).

The pressure required for the synthesis of crystals containing NF6- amounts to 400-500 thousand atmospheres which is within the reach of current experimental techniques. Simulations suggest that after formation the crystals would remain metastable even at much lower pressures. Does that also mean under normal atmospheric pressure?

"I wouldn't bet too much money on that, but it cannot be completely ruled out that one day you will simply be able to pick up the crystals we predict with unique NF6- ions. If they do turn out to be so stable, who knows, perhaps it will be possible to find some interesting applications for them?" wonders Dr. Zaleski-Ejgierd.

However, taking a crystal with NF6- ions into your hand would probably not be a very good idea. Nitrogen trifluoride is already a strong oxidizing agent that must be stored in steel cylinders. A crystal of nitrogen pentafluoride mixed with NF6- would be an even stronger oxidant and we can assume that even the construction of a container allowing for its safe storage could cause engineers considerable difficulties.
-end-
The Institute of Physical Chemistry of the Polish Academy of Sciences was established in 1955 as one of the first chemical institutes of the PAS. The Institute's scientific profile is strongly related to the newest global trends in the development of physical chemistry and chemical physics. Scientific research is conducted in nine scientific departments. CHEMIPAN R&D Laboratories, operating as part of the Institute, implement, produce and commercialise specialist chemicals to be used, in particular, in agriculture and pharmaceutical industry. The Institute publishes approximately 200 original research papers annually.

Institute of Physical Chemistry of the Polish Academy of Sciences

Related Nitrogen Articles:

'Black nitrogen'
In the periodic table of elements there is one golden rule for carbon, oxygen, and other light elements.
A deep dive into better understanding nitrogen impacts
This special issue presents a selection of 13 papers that advance our understanding of cascading consequences of reactive nitrogen species along their emission, transport, deposition, and the impacts in the atmosphere.
How does an increase in nitrogen application affect grasslands?
The 'PaNDiv' experiment, established by researchers of the University of Bern on a 3000 m2 field site, is the largest biodiversity-ecosystem functioning experiment in Switzerland and aims to better understand how increases in nitrogen affect grasslands.
Reducing reliance on nitrogen fertilizers with biological nitrogen fixation
Crop yields have increased substantially over the past decades, occurring alongside the increasing use of nitrogen fertilizer.
Flushing nitrogen from seawater-based toilets
With about half the world's population living close to the coast, using seawater to flush toilets could be possible with a salt-tolerant bacterium.
We must wake up to devastating impact of nitrogen, say scientists
More than 150 top international scientists are calling on the world to take urgent action on nitrogen pollution, to tackle the widespread harm it is causing to humans, wildlife and the planet.
How nitrogen-fixing bacteria sense iron
New research reveals how nitrogen-fixing bacteria sense iron - an essential but deadly micronutrient.
Corals take control of nitrogen recycling
Corals use sugar from their symbiotic algal partners to control them by recycling nitrogen from their own ammonium waste.
Foraging for nitrogen
As sessile organisms, plants rely on their ability to adapt the development and growth of their roots in response to changing nutrient conditions.
Inert nitrogen forced to react with itself
Direct coupling of two molecules of nitrogen: chemists from Würzburg and Frankfurt have achieved what was thought to be impossible.
More Nitrogen News and Nitrogen Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#566 Is Your Gut Leaking?
This week we're busting the human gut wide open with Dr. Alessio Fasano from the Center for Celiac Research and Treatment at Massachusetts General Hospital. Join host Anika Hazra for our discussion separating fact from fiction on the controversial topic of leaky gut syndrome. We cover everything from what causes a leaky gut to interpreting the results of a gut microbiome test! Related links: Center for Celiac Research and Treatment website and their YouTube channel
Now Playing: Radiolab

The Flag and the Fury
How do you actually make change in the world? For 126 years, Mississippi has had the Confederate battle flag on their state flag, and they were the last state in the nation where that emblem remained "officially" flying.  A few days ago, that flag came down. A few days before that, it coming down would have seemed impossible. We dive into the story behind this de-flagging: a journey involving a clash of histories, designs, families, and even cheerleading. This show is a collaboration with OSM Audio. Kiese Laymon's memoir Heavy is here. And the Hospitality Flag webpage is here.