Nitrogen triiodide

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Nitrogen triiodide
Image:Nitrogen-iodide-2D.png
Image:Nitrogen-triiodide-3D-vdW.png
Identifiers
CAS number	13444-85-4
Properties
Molecular formula	NI₃
Molar mass	394.77 g/mol
Density	? g/cm³
Melting point	sublimes -20 °C
Boiling point	°C
Solubility in other solvents	Decomposes
Related Compounds
Related iodides	Phosphorus triiodide Arsenic triiodide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Nitrogen triiodide, also called nitrogen iodide, is the chemical compound with the formula N I₃. It is a sensitive contact explosive: small quantities explode with a gunpowder-like snap when touched even lightly, releasing a purple cloud of iodine vapor. NI₃ has a complex structural chemistry that has required relatively heroic efforts to elucidate because of the instability of the derivatives.

Decomposition

The decomposition of NI₃ proceeds via the following reaction:

2NI₃(s) → N₂(g) + 3I₂(g) ΔH = –290 kJ/mol

Structure of NI₃ and its derivatives

Nitrogen triiodide is a dark red compound, first characterized by X-ray crystallography in 1990, when it was prepared by an ammonia-free route. Boron nitride reacts with iodine fluoride in trichlorofluoromethane at -30 °C to produce pure NI₃ in low yield.^[1] NI₃ is pyramidal (C_3v molecular symmetry), as are the other nitrogen trihalides as well as ammonia.^[1]

The material that is usually called "nitrogen triiodide" is prepared by the reaction of iodine with ammonia. When this reaction is conducted at low temperatures in anhydrous ammonia, the initial product is NI₃·(NH₃)₅, but this material loses some ammonia upon warming to give the 1:1 adduct NI₃·(NH₃). This adduct was first reported by Bernard Courtois in 1812, and its formula was finally determined in 1905 by Silberrad.^[1] Its solid state structure consists of chains of -NI₂-I-NI₂-I-NI₂-I-... Ammonia molecules are situated between the chains. In the dark and kept cold and damp with ammonia, NI₃·(NH₃) is stable. The dry material is, however a contact explosive decomposing according to the following equation:^[1]

8NI₃NH₃ → 5 N₂ + 6 NH₄I + 9 I₂

The instability of NI₃ itself or NI₃NH₃ can be attributed to the great stability of N₂.