Editing Nitrogen (section)

===Nitrides, azides, and nitrido complexes===
Nitrogen bonds to almost all the elements in the periodic table except the first two [[noble gas]]es, [[helium]] and [[neon]], and some of the very short-lived elements after [[bismuth]], creating an immense variety of binary compounds with varying properties and applications.<ref name="Greenwood412" /> Many binary compounds are known: with the exception of the nitrogen hydrides, oxides, and fluorides, these are typically called [[nitride]]s. Many stoichiometric phases are usually present for most elements (e.g. MnN, Mn<sub>6</sub>N<sub>5</sub>, Mn<sub>3</sub>N<sub>2</sub>, Mn<sub>2</sub>N, Mn<sub>4</sub>N, and Mn<sub>''x''</sub>N for 9.2 < ''x'' < 25.3). They may be classified as "salt-like" (mostly ionic), covalent, "diamond-like", and metallic (or [[interstitial compound|interstitial]]), although this classification has limitations generally stemming from the continuity of bonding types instead of the discrete and separate types that it implies. They are normally prepared by directly reacting a metal with nitrogen or ammonia (sometimes after heating), or by [[thermal decomposition]] of metal amides:<ref name="Greenwood417">Greenwood and Earnshaw, pp. 417–20</ref>
:3 Ca + N<sub>2</sub> → Ca<sub>3</sub>N<sub>2</sub>
:3 Mg + 2 NH<sub>3</sub> → Mg<sub>3</sub>N<sub>2</sub> + 3 H<sub>2</sub> (at 900&nbsp;°C)
:3 Zn(NH<sub>2</sub>)<sub>2</sub> → Zn<sub>3</sub>N<sub>2</sub> + 4 NH<sub>3</sub>
Many variants on these processes are possible. The most ionic of these nitrides are those of the [[alkali metal]]s and [[alkaline earth metal]]s, Li<sub>3</sub>N (Na, K, Rb, and Cs do not form stable nitrides for steric reasons) and M<sub>3</sub>N<sub>2</sub> (M = Be, Mg, Ca, Sr, Ba). These can formally be thought of as salts of the N<sup>3−</sup> anion, although charge separation is not actually complete even for these highly electropositive elements. However, the alkali metal [[azide]]s NaN<sub>3</sub> and KN<sub>3</sub>, featuring the linear {{chem|N|3|-}} anion, are well-known, as are Sr(N<sub>3</sub>)<sub>2</sub> and Ba(N<sub>3</sub>)<sub>2</sub>. Azides of the B-subgroup metals (those in [[group 11 element|groups 11]] through [[chalcogen|16]]) are much less ionic, have more complicated structures, and detonate readily when shocked.<ref name="Greenwood417" />

[[File:Borazin Mesomers1.svg|thumb|right|upright=1.8|Mesomeric structures of borazine, (–BH–NH–)<sub>3</sub>]]
Many covalent binary nitrides are known. Examples include [[cyanogen]] ((CN)<sub>2</sub>), [[triphosphorus pentanitride]] (P<sub>3</sub>N<sub>5</sub>), [[disulfur dinitride]] (S<sub>2</sub>N<sub>2</sub>), and [[tetrasulfur tetranitride]] (S<sub>4</sub>N<sub>4</sub>). The essentially covalent [[silicon nitride]] (Si<sub>3</sub>N<sub>4</sub>) and [[germanium nitride]] (Ge<sub>3</sub>N<sub>4</sub>) are also known: silicon nitride, in particular, would make a promising [[ceramic]] if not for the difficulty of working with and sintering it. In particular, the [[boron group|group 13]] nitrides, most of which are promising [[semiconductor]]s, are isoelectronic with graphite, diamond, and [[silicon carbide]] and have similar structures: their bonding changes from covalent to partially ionic to metallic as the group is descended. In particular, since the B–N unit is isoelectronic to C–C, and carbon is essentially intermediate in size between boron and nitrogen, much of [[organic chemistry]] finds an echo in boron–nitrogen chemistry, such as in [[borazine]] ("inorganic [[benzene]]"). Nevertheless, the analogy is not exact due to the ease of [[nucleophile|nucleophilic]] attack at boron due to its deficiency in electrons, which is not possible in a wholly carbon-containing ring.<ref name="Greenwood417" />

The largest category of nitrides are the interstitial nitrides of formulae MN, M<sub>2</sub>N, and M<sub>4</sub>N (although variable composition is perfectly possible), where the small nitrogen atoms are positioned in the gaps in a metallic cubic or [[hexagonal close-packed]] lattice. They are opaque, very hard, and chemically inert, melting only at very high temperatures (generally over 2500&nbsp;°C). They have a metallic lustre and conduct electricity as do metals. They hydrolyse only very slowly to give ammonia or nitrogen.<ref name="Greenwood417" />

The nitride anion (N<sup>3−</sup>) is the strongest ''π'' donor known among ligands (the second-strongest is O<sup>2−</sup>). Nitrido complexes are generally made by the thermal decomposition of azides or by deprotonating ammonia, and they usually involve a terminal {≡N}<sup>3−</sup> group. The linear azide anion ({{chem|N|3|-}}), being isoelectronic with [[nitrous oxide]], [[carbon dioxide]], and [[cyanate]], forms many coordination complexes. Further catenation is rare, although {{chem|N|4|4-}} (isoelectronic with [[carbonate]] and [[nitrate]]) is known.<ref name="Greenwood417" />