Sodium nitride is the inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula Na₃N. In contrast to lithium nitride

Lithium nitride

Lithium nitride is a compound of lithium and nitrogen with the formula Li3N. It is the only stable alkali metal nitride...

 and many other nitride

Nitride

In chemistry, a nitride is a compound of nitrogen where nitrogen has a formal oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications....

s, sodium nitride is an extremely unstable alkali metal

Alkali metal

The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...

 nitride

Nitride

In chemistry, a nitride is a compound of nitrogen where nitrogen has a formal oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications....

. It can be generated by combining atomic beams of sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 and nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 deposited onto a low-temperature sapphire

Sapphire

Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide , when it is a color other than red or dark pink; in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give...

substrate.
It decomposes into its elements:

2 Na₃N → 6 Na + N₂

Synthesis

Sodium nitride can be synthesized in two different ways: by the thermal decomposition of NaNH₂ or by the direct reaction of the elements. The most common way to successfully synthesize sodium nitride has been done by Dieter Fischer & Martin Jansen and Grigori Vajenine using the latter method. The first way is to introduce desired ratios of Na and N₂ in gas phase separately and depositing them in a vacuum chamber on a cooled substrate, which is then heated to room temperate (298K) to crystallize.
The second method is to react elemental sodium with plasma activated nitrogen on a metal surface. This synthesis can be further facilitated by introducing liquid Na-K alloy to the compound with the excess liquid removed and washed with fresh alloy. The solid is then separated from the liquid using a centrifuge. However Vajenine’s method is very air-sensitive and can decompose and combust rapidly, unless exposed to a pure oxygen (O₂) environment.

Characteristics

Sodium nitride can be of reddish brown or dark blue color depending on the synthesis of the compound due to intrinsic properties. It shows no signs of decomposition after several weeks when at room temperature. The compound does not have a melting point as it decomposes back into its elemental forms as demonstrated using mass spectrometry around 360K. The estimated enthalpy of formation for the compound is +64 kJ/mol.

Structure

Sodium Nitride seems to be about 90% ionic at room temperature but has the band gap typical for a semiconductor. It adopts the anti-ReO₃ structure with a simple lattice made up of NNa₆ octahedrons. The compound has N-Na bond lengths of 236.6pm. This structure has been confirmed through X-ray diffraction and more recently neutron diffraction on powder and single-crystals.