Nitride
1216060
210552911
2008-05-06T12:32:51Z
Albmont
1912742
pt:
In chemistry a '''nitride''' is a compound of [[nitrogen]] with a less [[electronegative]] element where nitrogen has an [[oxidation state]] of -3. Note that there are exceptions to this naming convention, the nitrides of hydrogen, NH<sub>3</sub> and carbon, (CN)<sub>2</sub>, are called [[ammonia]] and [[cyanogen]] respectively and that the nitrides of bromine, iodine are called [[nitrogen tribromide]] and [[nitrogen triiodide]]. Note that nitrogen also forms pernitrides, that contain N<sub>2</sub><sup>2<nowiki>−</nowiki></sup> and azides, that contain N<sub>3</sub><sup><nowiki>−</nowiki></sup>.
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Nitrogen has one of the highest [[electronegative|electronegativities]], only oxygen, fluorine and chlorine (in Paulling & Mulliken scales) are higher. This means that the nitrides are a very large group of compounds. They have wide range of properties and applications.
*refractory materials e.g.
*lubricant e.g. hexagonal [[boron nitride]], BN
*cutting materials e.g. [[silicon nitride]], Si<sub>3</sub>N<sub>4</sub>
*insulators e.g. [[boron nitride]], BN, [[silicon nitride]], Si<sub>3</sub>N<sub>4</sub>
*semiconductors e.g. [[gallium nitride]], GaN
*metal coatings e.g. [[titanium nitride]], TiN
*hydrogen storage e.g [[Lithium nitride]], Li<sub>3</sub>N
Classification of such a varied group of compounds is necessarily arbitrary. The following is based around their structure:
*salt like, e.g. [[lithium nitride]], Li<sub>3</sub>N, [[beryllium nitride]], Be<sub>3</sub>N<sub>2</sub>
*covalent
**3 dimensional structures e.g. phosphorus nitride, P<sub>3</sub>N<sub>5</sub>; [[boron nitride]], BN
**diamond like e.g. [[gallium nitride]], GaN
**molecular ("volatile") e.g. [[tetrasulfur tetranitride]], S<sub>4</sub>N<sub>4</sub>
*interstitial e.g. [[titanium nitride]], TiN
*intermediate e.g. iron nitride, Fe<sub>2</sub>N
===Nitride ion===
The '''nitride''' [[ion]] is N<sup>3−</sup> (a nitrogen atom plus three electrons). The extra electrons give the nitrogen atom a closed inert gas shell. The nitride ion is [[isoelectronic]] with the [[oxide]] anion, O<sup>2<nowiki>−</nowiki></sup>, and the [[fluoride]] anion, F<sup><nowiki>−</nowiki></sup> and has an ionic radius estimated to be 140 pm. The nitride ion is a strong π-donor ligand, stronger than O<sup>2−</sup>. It forms nitrido complexes which have a short metal nitrogen bond length indicating multiple bonding.
===Salt like nitrides===
The salt like nitrides are formed by:
*the alkali metals, [[Lithium nitride|Li<sub>3</sub>N]], Na<sub>3</sub>N and K<sub>3</sub>N. Li<sub>3</sub>N is readily formed and has a unique structure. Na<sub>3</sub>N <ref>''Synthesis and structure of Na<sub>3</sub>N'', Fischer, D., Jansen, M. Angew Chem Intnl 41, 10, 1755 (2002) DOI:10.1002/1521-3773(20020517)41:10<1755::AID-ANIE1755>3.0.CO;2-C</ref> and K<sub>3</sub>N <ref>''Synthesis and structure of K<sub>3</sub>N'', Fischer, D.; Cancarevic, Z.; Schön, J. C.; Jansen, M. Z. fur anorg allgem Chemie, 630, 1, 156, DOI: 10.1002/zaac.200300280</ref> have been synthesised by simultaneously depositing metal atoms and nitrogen atoms onto a [[liquid nitrogen]] cooled sapphire substrate. Both are unstable compounds.
*the alkaline earth metals [[magnesium nitride|Mg<sub>3</sub>N<sub>2</sub>]], [[beryllium nitride|Be<sub>3</sub>N<sub>2</sub>]] and [[calcium nitride|Ca<sub>3</sub>N<sub>2</sub>]]
*the [[group 3 element|group 3]] metals e.g. scandium nitride, ScN
*the [[group 11 element|group 11]] metals e.g. copper nitride, Cu<sub>3</sub>N
*the [[group 12 element|group 12]] metals e.g. [[zinc nitride|Zn<sub>3</sub>N<sub>2</sub>]]
[[Lithium nitride]] and the alkaline earth nitrides deprotonate hydrogen gas, and are rapidly hydrolysed by water to form ammonia.
===Covalent nitrides===
;3 dimensional structures
:These include, boron nitride silicon and phosphorus.
;Diamond like nitrides
:The diamond like nitrides of [[aluminium nitride|aluminium]], [[gallium nitride|gallium]] and [[indium nitride|indium]] all have the [[wurtzite]] structure in which each atom occupies tetrahedral sites. For example in aluminium nitride, each aluminium atom has four neighbouring nitrogen atoms at the corners of a tetrahedron and similarly each nitrogen atom has four neighbouring aluminium atoms at the corners of a tetrahedron. This structure is like hexagonal diamond (Lonsdaleite) where every carbon atom occupies a tetrahedral site (however wurzite differs from [[sphalerite]] and [[diamond]] in the relative orientation of tetrahedra) Note that thallium(III) nitride, TlN is not known, whereas thallium(I) nitride, Tl<sub>3</sub>N is.
;Molecular
:These include [[cyanogen]], (CN)<sub>2</sub> and S<sub>2</sub>N<sub>2</sub> and [[tetrasulfur tetranitride]], S<sub>4</sub>N<sub>4</sub>. (Note that sulfur forms another nitride which is polymeric, [[tetrasulfur tetranitride|(SN)<sub>x</sub>]], this is a metallic conductor and has been called a one-dimensional metal.)
===Interstitial nitrides===
The interstitial nitrides are formed by transition metals where there is a sufficient difference in size between the metal atom and the nitrogen to allow the host metal lattice to accommodate the nitrogen atom. This condition is true for the [[group 4 element|group 4]], [[group 5 element|5]] and [[group 6 element|6]] transition metals i.e. the Titanium, Vanadium and Chromium groups. The group 4 and 5 nitrides are [[refractory]] i.e. high melting and chemically stable.
===Intermediate nitrides===
[[group 7 element|Group 7]] and [[group 8 element|8]] transition metals form nitrides that decompose readily e.g iron nitride, Fe<sub>2</sub>N melts with decomposition at 200<sup>o</sup>C. The precious metals are currently being investigated by a number of researchers and thin films of platinum, gold and osmium nitrides have been produced. However there is some discussion as to their structures and their properties. Platinum nitride and osmium nitride for example are now believed to contain N<sub>2</sub> units and as such should not be called nitrides.
<ref>''Gold film with gold nitride-A conductor but harder than gold'', L. Siller, N. Peltekis, S. Krishnamurthy, Y. Chao, S.J. Bull, M.R.C. Hunt, Appl. Phys. Lett. 86, 22, 221912, (2005) DOI: 10.1063/1.1941471</ref>
<ref> ''OsN<sub>2</sub>: Crystal structure and electronic properties'', J. A. Montoya, A.D Hernandez, C. Sanloup, E Gregoryanz, S Scandolo, Appl. Phys. Lett. 90, 1, 011909 (2007) DOI: 10.1063/1.2430631</ref>
== General references ==
* [http://www.webelements.com/ WebElements]
*{{Greenwood&Earnshaw}}
*H.O Pierson (1996). ''Handbook of refractory carbides and nitrides'', William Andrew Inc. ISBN 0-8155-1392-5
== Footnotes ==
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