In chemistry, a nitride is a chemical compound of nitrogen. Nitrides can be inorganic or Organic compound, ionic or covalent. The nitride anion, N3−, is very elusive but compounds of nitride are numerous, although rarely naturally occurring. Some nitrides have a found applications,
Synthesis of inorganic metal nitrides is challenging because nitrogen gas (N2) is not very reactive at low temperatures, but it becomes more reactive at higher temperatures. Therefore, a balance must be achieved between the low reactivity of nitrogen gas at low temperatures and the entropy driven formation of N2 at high temperatures.
Uses of nitrides
Like
, nitrides are often refractory materials owing to their high
lattice energy, which reflects the strong bonding of "N
3−" to metal cation(s). Thus, cubic boron nitride,
titanium nitride, and
silicon nitride are used as cutting materials and hard coatings. Hexagonal
boron nitride, which adopts a layered structure, is a useful high-temperature lubricant akin to molybdenum disulfide. Nitride compounds often have large
, thus nitrides are usually insulators or wide-bandgap semiconductors; examples include
boron nitride and silicon nitride. The wide-band gap material
gallium nitride is prized for emitting blue light in
.
Like some oxides, nitrides can absorb hydrogen and have been discussed in the context of
hydrogen storage, e.g.
lithium nitride.
Examples
Classification of such a varied group of compounds is somewhat arbitrary. Compounds where nitrogen is not assigned −3 oxidation state are not included, such as nitrogen trichloride where the oxidation state is +3; nor are
ammonia and its many organic derivatives.
Nitrides of the s-block elements
Only one
alkali metal nitride is stable, the purple-reddish
lithium nitride (), which forms when lithium burns in an atmosphere of .
Both
Sodium nitride and potassium nitride have been synthesized, but remain a laboratory curiosity. The nitrides of the alkaline earth metals that have the formula are however numerous. Examples include beryllium nitride (), magnesium nitride (),
calcium nitride (), and strontium nitride (). The nitrides of electropositive metals (including Li, Zn, and the alkaline earth metals) readily hydrolyze upon contact with water, including the moisture in the air:
Nitrides of the p-block elements
Boron nitride exists as several forms (polymorphs). Nitrides of
silicon nitride and phosphorus are also known, but only the former is commercially important. The nitrides of aluminium,
gallium nitride, and
indium nitride adopt the hexagonal wurtzite structure in which each atom occupies tetrahedral sites. For example, in aluminium nitride, each aluminium atom has four neighboring nitrogen atoms at the corners of a tetrahedron and similarly each nitrogen atom has four neighboring aluminium atoms at the corners of a tetrahedron. This structure is like hexagonal diamond (
lonsdaleite) where every carbon atom occupies a tetrahedral site (however wurtzite differs from
sphalerite and
diamond in the relative orientation of tetrahedra).
Thallium nitride () is known, but thallium(III) nitride (TlN) is not.
Transition metal nitrides
Most metal-rich transition metal nitrides adopt a relatively ordered face-centered cubic or hexagonal close-packed crystal structure, with octahedral coordination.
Sometimes these materials are called "interstitial nitrides". They are essential for industrial
metallurgy, because they are typically much
Hardness and less
ductile than their parent metal, and resist air-oxidation.
For the group 3 metals, ScN and
yttrium nitride are both known. Group 4, 5, and 6 transition metals (the titanium, vanadium and chromium groups) all form
chemically stable,
refractory nitrides with high melting point.
of
titanium nitride, zirconium nitride, and
tantalum nitride protect many industrial surfaces.
Nitrides of the group 7 and 8 transition metals tend to be nitrogen-poor, and decompose readily at elevated temperatures. For example, iron nitride, decomposes at 200 °C. Platinum nitride and osmium nitride may contain units, and as such should not be called nitrides.
Nitrides of heavier members from group 11 and 12 are less stable than copper nitride () and zinc nitride (): dry Silver nitride is a contact explosive which may detonate from the slightest touch, even a falling water droplet.
Nitrides of the lanthanides and actinides
Nitride containing species of the lanthanides and actinides are of scientific interest as they can provide a useful handle for determining covalency of bonding. Nuclear magnetic resonance (NMR) spectroscopy along with quantum chemical analysis has often been used to determine the degree to which metal nitride bonds are ionic or covalent in character. One example, a uranium nitride, has the highest known nitrogen-15 chemical shift.
Molecular nitrides
Many metals form molecular nitrido complexes, as discussed in the specialized article. The main group elements also form some molecular nitrides.
Cyanogen () and tetrasulfur tetranitride () are rare examples of a molecular binary (containing one element aside from nitrogen) nitrides. They dissolve in nonpolar solvents. Both undergo polymerization. is also unstable with respect to the elements, but less so that the isostructural . Heating gives a polymer, and a variety of molecular sulfur nitride anions and cations are also known.
Related to but distinct from nitride is pernitride diatomic anion () and the azide triatomic anion (N3−).
it is Nitride
