The inorganic imides are compounds containing an ion composed of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

bonded to

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

with formula HN²⁻. Organic

imide In organic chemistry, an imide is a functional group consisting of two acyl groups bound to nitrogen. The compounds are structurally related to acid anhydrides, although imides are more resistant to hydrolysis. In terms of commercial applications, ...

s have the NH group, and two single or one double covalent bond to other atoms. The imides are related to the inorganic amides (H₂N⁻), the

nitride In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...

s (N³⁻) and the nitridohydrides (N³⁻•H⁻). In addition to solid state imides, molecular imides are also known in dilute gases, where their spectrum can be studied. Imide can be a ligand, with a double bond to a metal such as molybdenum (e.g. Mo=NH). As a ligand it is called imido. The imido ligand is part of a nitrogen fixation cycle: Mo•N₂ → Mo-N=N⁻ → Mo-N=NH (diazenido) → Mo-N=NH₂⁺ → Mo=N-NH₂ (hydrazido) → Mo=N-NH₃⁺ (hydrazidium) → Mo≡N (nitrido) + NH₃ → Mo≡NH⁺ → Mo=NH (imido) → Mo=NH₂⁺ → Mo-NH₂ (amido) → Mo-NH₃⁺ → Mo•NH₃ (ammine); with the oxidation state of molybdenum varying to accommodate the number bonds from nitrogen. When the hydrogen of the imide group is substituted by an organic group, an organoimide results. Complexes of

actinide The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...

and

rare earth element The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...

s with organoimides are known.

Properties

Lithium imide undergoes a phase transition at 87 °C where it goes from an ordered to a more symmetric disordered state.

Structure

Many imides have a cubic rock salt structure, with the metal and nitrogen occupying the main positions. The position of the hydrogen atom is hard to determine, but is disordered. Many of the heavy metal simple imide molecules are linear. This is due to the filled 2p orbital of nitrogen donating electrons to an empty d orbital on the metal.

Formation

Heating

lithium amide Lithium amide or lithium azanide is an inorganic compound with the chemical formula . It is a white solid with a tetragonal crystal structure. Lithium amide can be made by treating lithium metal with liquid ammonia: : Other lithium amides The co ...

with

lithium hydride Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...

yields lithium imide and hydrogen gas. This reaction takes place as released

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

reacts with lithium hydride. Heating magnesium amide to about 400 °C yields magnesium imide with the loss of

. Magnesium imide itself decomposes if heated between 455 and 490 °C. Beryllium imide forms from beryllium amide when heated to 230 °C in a vacuum. When strontium metal is heated with ammonia at 750 °C, the dark yellow strontium imide forms. When barium vapour is heated with ammonia in an electrical discharge, the gaseous, molecular BaNH is formed. Molecules ScNH, YNH, and LaNH are also known.

Hydrogen storage

Inorganic imides are of interest because they can reversibly store hydrogen, which may be important for the

hydrogen economy The hydrogen economy is using hydrogen to decarbonize economic sectors which are hard to electrify, essentially, the "hard-to-abate" sectors such as cement, steel, long-haul transport etc. In order to phase out fossil fuels and limit climate ch ...

. For example, calcium imide can store 2.1% mass of hydrogen. Li₂Ca(NH)₂ reversibly stores hydrogen and release it at temperatures between 140 and 206 °C. It can reversibly hold 2.3% hydrogen. When hydrogen is added to the imide, amides and hydrides are produced. When imides are heated, they can yield

hydridonitrides In chemistry, a hydridonitride (nitridohydride, nitride hydride, or hydride nitride) is a chemical compound that contains hydride () and nitride () ions in a single Phase (matter), phase. These inorganic compounds are distinct from inorganic Metal ...

or nitrides, but these may not easily reabsorb hydrogen.

List

Ionic

Molecular

Molecular imines of other actinides called neptunimine and plutonimine have been postulated to exist in the gas phase or noble gas matrix.

References

{{Reflist Nitrogen compounds Hydrogen compounds