Crystal structure of uranium nitride, UN. The structure is face-centered cubic with a lattice constant of 4889 ± 0.001 Å at 26°C and sodium chloride type. The theoretical density is 14315 kg m–3, and the U—N bond distance for coordination number 6 is 2.4449 Å.Crystallographic Data. 177. Uranium Mononitride, , Analytical Chemistry, 01/1959, Volume 31, Issue 1, p.156 - 157, (1959)
Everyone knows that elemental nitrogen exists in the atmosphere as dinitrogen, N2. There is a triple bond between the two nitrogen atoms. This is true - but under certain conditions, a fascinating N-N single bonded phase has been characterized.1
In 1985 it was predicted that at high pressure, nitrogen would transform to a solid with a single-bonded crystalline structure called polymeric nitrogen. Later, it was proposed that it whould have a cubic gauche (cg-N) structure. Experimental evidence was scant however until 2004 when a team of scientists from Germany and Russia managed to make the compound directly from molecular nitrogen at temperatures above 2000 K and pressures above 110 GPa using a laser-heated diamond cell. The material was characterized by X-ray and Raman scattering methods we have identified this as the polymeric nitrogen (cg-N).
The phase is a stiff with a bulk modulus ≥300 GPa. This is characteristic of strong covalent solids. The polymeric nitrogen is metastable. The structure of N is polymeric with each nitrogen bound to three other nitrogen atoms. At a pressure of 115 GPa, each N-N bond length is 1.346 ± 0.004 Å. The N-N-N angles are all about 108.8°, very close to the ideal tetrahedral angle of just over 109°.
It did not prove possible to recover the polymeric nitrogen by releasing the pressure - in other words the polymer reverts to normal dinitrogen. The authors speculate that this form of nitrogen is a new class of single-bonded nitrogen materials that may have unique energy capacity properties (more than five times that of the most powerful energetic materials).
Abstract: Nitrogen usually consists of molecules where two atoms are strongly triple-bonded. Here, we report on an allotropic form of nitrogen where all atoms are connected with single covalent bonds, similar to carbon atoms in diamond. The compound was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressures above 110 GPa using a laser-heated diamond cellSingle-bonded cubic form of nitrogen, , Nature Materials, 8/2004, Volume 3, Issue 8, p.558 - 563, (2004)
An egg-shaped fullerene, or "buckyball egg" has been made and characterized by chemists in America at UC Davis (California), Virginia Tech, and Emory and Henry College in Virginia. They were trying to encapsulate terbium atoms within fullerenes but instead encapsulated terbium nitride within an egg-shaped fullerene.1
The compound Tb3N@C84 was synthesized using an arc-discharge generator by vaporizing composite graphite rods containing a mixture of Tb4O7, graphite, and iron nitride as catalyst in a low-pressure He/N2atmosphere. This gave a complex mixture of products and chromatography gave seven terbium-containing fractions, the fourth fraction of which contained two isomers of Tb3N@C84. Crystallographc studies show the compound from one angle in particular seems very egg shaped! Remarkable! The Tb3N unit is clearly visible (terbium in green and nitrogen in blue).
Until the publication of this work it was normally accepted that no two pentagons can touch in a fullerene and are always surrounded by hexagons. However in this case there are two pentagons (the 8 atoms at the pointy part of the egg at the top of the attached image) linked as a bent pentalene fragment.
- 1. Tb3N@C84 : An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule,
, Journal of the American Chemical Society, 09/2006, Volume 128, Issue 35, p.11352 - 11353, (2006)
Abstract.The structure of isomer 2 of Tb3N@C84 has been determined through single-crystal X-ray diffraction on Tb3N@C84·NiII(OEP)·2(C6H6). The carbon cage has a distinct egg shape due to the presence of a single pair of fused pentagons at one apex of the molecule. Thus, although 24 IPR structures are available to the C84 cage, Nature utilizes one of the 51 568 isomeric structures that do not conform to the IPR for this unusual molecule. The Tb3N portion of isomer 2 of Tb3N@C84 is strictly planar. One Tb atom is nestled within the fold of the fused pentagons, while the other Tb atoms are disordered over four pairs of sites.Tb3N@C84 : An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule, , Journal of the American Chemical Society, 09/2006, Volume 128, Issue 35, p.11352 - 11353, (2006)
Modern surface chemistry – fuel cells, artificial fertilizers and clean exhaust
The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Chemistry for 2007 to Gerhard Ertl of the Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany "for his studies of chemical processes on solid surfaces".
The Nobel Prize in Chemistry for 2007 is awarded for groundbreaking studies in surface chemistry. This science is important for the chemical industry and can help us to understand such varied processes as why iron rusts, how fuel cells function and how the catalysts in our cars work. Chemical reactions on catalytic surfaces play a vital role in many industrial operations, such as the production of artificial fertilizers. Surface chemistry can even explain the destruction of the ozone layer, as vital steps in the reaction actually take place on the surfaces of small crystals of ice in the stratosphere. The semiconductor industry is yet another area that depends on knowledge of surface chemistry.
It was thanks to processes developed in the semiconductor industry that the modern science of surface chemistry began to emerge in the 1960s. Gerhard Ertl was one of the first to see the potential of these new techniques. Step by step he has created a methodology for surface chemistry by demonstrating how different experimental procedures can be used to provide a complete picture of a surface reaction. This science requires advanced high-vacuum experimental equipment as the aim is to observe how individual layers of atoms and molecules behave on the extremely pure surface of a metal, for instance. It must therefore be possible to determine exactly which element is admitted to the system. Contamination could jeopardize all the measurements. Acquiring a complete picture of the reaction requires great precision and a combination of many different experimental techniques.
Gerhard Ertl has founded an experimental school of thought by showing how reliable results can be attained in this difficult area of research. His insights have provided the scientific basis of modern surface chemistry: his method-ology is used in both academic research and the indust-rial development of chemical processes. The approach developed by Ertl is based not least on his studies of the Haber-Bosch process, in which nitrogen is extracted from the air for inclusion in artificial fertilizers. This reaction, which functions using an iron surface as its catalyst, has enormous economic significance because the availability of nitrogen for growing plants is often restricted. Ertl has also studied the oxidation of carbon monoxide on platinum, a reaction that takes place in the catalyst of cars to clean exhaust emissions.
Sequel to an Essay on the Constitution of the Atmosphere, Published in the Philosophical Transactions for 1826; With Some Account of the Sulphurets of Lime
The complete archive of the Royal Society journals, including some of the most significant scientific papers ever published since 1665, is to be made freely available electronically for the first time until 2007.
The archive contains seminal research papers including accounts of Michael Faraday's groundbreaking series of electrical experiments, Isaac Newton's invention of the reflecting telescope, and the first research paper published by Stephen Hawking.
The Society's online collection, which until now only extended back to 1997, contains every paper published in the Royal Society journals from the first ever peer-reviewed scientific journal, Philosophical Transactions in 1665, to the most recent addition, Interface.
You can register for free. So now, for a time at least, you can read free of charge some extraordinary historical documents. Here are a few examples:
- On the Constitution of the Atmosphere by John Dalton
- On the Action of Radium Emanations on Diamond by William Crookes
- The Separation of the Most Volatile Gases from Air without Liquefaction by James Dewar
- On the Compressibilities of Oxygen, Hydrogen, Nitrogen, and Carbonic Oxide between One Atmosphere and Half an Atmosphere of Pressure, and on the Atomic Weights of the Elements Concerned.--Preliminary Notice by Lord Rayleigh
Note: this facility seems to have been withdrawn?