Nitrides

As nitrides is defined as the chemical compounds of nitrogen (lat .: Nitrogenium ) to another, less electronegative element. In these compounds, nitrogen is formally assigned a three-fold negative charge ( oxidation number ) (N ³⁻ : nitride anion ). Nitrides can be classified according to the character of the prevailing bond type. Ionic (salt-like) nitrides are used when the binding partner is a strongly electropositive metal such as B. lithium is in lithium nitride . Metallic nitrides often form together with transition metals, such as the various iron nitrides . In the case of non-metals or semimetals as binding partners, mainly covalently bound, three-dimensional solids such as aluminum nitride or - more rarely - typical molecular compounds such as ammonia ("hydrogen nitride ") are formed, the salts or derivatives of which, the nitrides, can be understood as their salts or derivatives .

The nitrides are not to be confused with the nitrites (NO ₂ ^- ), the salts of nitrous acid .

Examples

Covalent nitrides

Covalent nitrides are partly diamond-like (example: boron nitride), partly very reactive and unstable (example: iodine nitrogen ). But boron nitride can also be chemically converted, e.g. B. to iodine nitrogen - for the first time in 1990 from boron nitride and iodine fluoride at −30 ° C in trichlorofluoromethane .

${\displaystyle \mathrm {BN+3\ IF\ {\xrightarrow {-30\,^{\circ }\mathrm {C} }}\ NI_{3}+BF_{3}} }$

Covalent nitrides are formed with the elements of the 3rd to 5th main group . Important covalent nitrides besides boron nitride (BN) with elements of the 3rd main group are aluminum nitride (AlN) and gallium nitride (GaN) as well as indium nitride (InN). With elements of the 4th main group, carbon nitrides (C ₃ N ₄ , subject of current research, theoretically harder than diamond), silicon nitride (Si ₃ N ₄ , for high-strength, high-temperature-resistant technical ceramics), germanium nitride (Ge ₃ N ₄ ), and tin are formed (IV) nitride (Sn ₃ N ₄ ). Also phosphorus nitride (P ₃ N ₅ ) is one of the covalent nitrides, as well as the nitrides of nobler metals such as: copper (I) nitride (Cu ₃ N).

Metallic nitrides

Metallic nitrides are usually interstitial compounds (like interstitial alloys) and form very hard crystals. They are formed by the transition metals of the 4th to 8th subgroups. As hard materials are here u. a. to mention: titanium nitride (TiN, in hardened and tempered layers on drills, milling cutters, hard metal indexable inserts), tantalum nitride (TaN), chromium nitride (CrN, tempering of special tools made of chromium). When steel is nitrided, iron nitride phases such as Fe ₄ N and Fe ₃ N _{1 + x} as well as nitrides of various alloying elements are created .

Ionic nitrides

Ionic nitrides are substances with a salty character. They react with water and acids to form ammonia gas and metal hydroxides, as the nitride ion is protonated ( acid-base reaction ). So z. B. Magnesium ammonia are produced: In the combustion of magnesium powder produced magnesium nitride as a yellow solid (for example, during the heating of metallic magnesium at about 600 ° C under a nitrogen atmosphere instead of air), reaction equation :

${\displaystyle \mathrm {3\ Mg+\ N_{2}\longrightarrow \ Mg_{3}N_{2}} }$

(When magnesium metal is burned in air, it is formed in addition to magnesium oxide (MgO) and makes it appear yellowish). This salt-like magnesium nitride then hydrolyzes with water to form magnesium hydroxide and ammonia gas :

${\displaystyle \mathrm {Mg_{3}N_{2}+6\ H_{2}O\longrightarrow 3\ Mg(OH)_{2}+2\ NH_{3}} }$

The group of salt-like nitrides, which also react with water, includes alkali nitrides such as lithium nitride (Li ₃ N) and sodium nitride (Na ₃ N), the alkaline earth nitrides include beryllium nitride (Be ₃ N ₂ , partly covalent), the above-mentioned magnesium nitride (Mg ₃ N ₂ ) and calcium nitride (Ca ₃ N ₂ ). Ionic nitrides also exist with other, electropositive subgroup metals, e.g. B. zinc nitride (Zn ₃ N ₂ ), scandium nitride (ScN), yttrium nitride (YN), lanthanum nitride ( LaN), zirconium (IV) nitride (Zr ₃ N ₄ ), tantalum (V) nitride (Ta ₃ N ₅ ) , Uranium nitride (UN, U ₂ N ₃ , UN ₂ ) and thorium (IV) nitride (Th ₃ N ₄ ).

use

Most technically used nitrides are used for surface hardening. So you use z. B. silicon nitride (Si ₃ N ₄ ) as an anti-reflective layer . Metal-like and so-called diamond-like nitrides serve as hard materials, high-temperature and refractory ceramic materials, e.g. B. Titanium Nitride (TiN).

Nitrides are also used in microelectronics . There they are used as diffusion barriers (e.g. tantalum nitride) or passivation layers (especially silicon nitride).

Nitrides of elements of the 3rd main group (AlN, GaN, InN) are III-V semiconductors and are used in electro-optical devices because of their large band gap to generate light with short wavelengths (blue). Requirement for the function of white LEDs .

Occurrence of nitrides in nature

Minerals

Nitride minerals are extremely rare. They can only form under oxygen-free conditions. This results from the much higher reactivity of oxygen O ₂ (“diradical”, dissociation enthalpy 498.67 kJ / mol) compared to nitrogen N ₂ (triple bond, dissociation enthalpy 946.04 kJ / mol).

• Roaldite (Fe ₄ N)
• Siderazot (Fe ₃ N)
• Osbornite (TiN)
• Carlsbergite (CrN)
• Sinoite (Si ₂ ON ₂ )

Individual evidence

1. ↑ Hans P. Latscha, Helmut A. Klein: Inorganic Chemistry (= chemistry basic knowledge. Vol. 1). 8th edition Springer, Berlin 2002, ISBN 3-540-42938-7 , p. 312 ff.
2. ^ ^{A b} E. Riedel, C. Janiak: Inorganic Chemistry . 8th edition. de Gruyter, 2011, ISBN 3-11-022566-2 , p. 474 f .
3. ↑ ^{a b} M. Binnewies et alii: Allgemeine und Anorganische Chemie . 2nd Edition. Spectrum, 2010, ISBN 3-8274-2533-6 , pp. 475 .