IUPAC name
3D model (JSmol)
  • InChI=1S/NO4/c2-1(3,4)5/q-3
  • [N+]([O-])([O-])([O-])[O-]
Molar mass 78.006
Conjugate acid Orthonitric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Orthonitrate is a tetrahedral anion of nitrogen with the formula NO3−
. It was first identified in 1977[1] and is currently known in only two compounds, sodium orthonitrate (Na3NO4) and potassium orthonitrate (K3NO4). The corresponding oxoacid, orthonitric acid (H3NO4) (also known as azoric acid), is hypothetical and has never been observed. Sodium and potassium orthonitrate can be prepared by fusion of the nitrate and metal oxide under high temperatures[2] and ideally high pressures (several GPa).[3]

NaNO3 + Na2O → Na3NO4 (300 °C for 3 days)[4]

The resulting orthonitrates are white solids which are extremely sensitive to moisture and CO2, decomposing within minutes to hydroxides, carbonates, and nitrates upon exposure to air.[1]

Na3NO4 + CO2 → NaNO3 + Na2CO3
Na3NO4 + H2O → NaNO3 + 2 NaOH

The orthonitrate ion is tetrahedral with N–O bond lengths of 139 pm, which is unexpectedly short, indicating that polar interactions are shortening the bond.[4] This short bond length parallels that of oxyanions containing third-row elements like PO3−
and SO2−
, for which pπ–dπ bonding was previously proposed as the explanation for the short bond length. Since 3d orbitals of nitrogen are much too high in energy to be involved in the case of orthonitrate, the shortness of the N–O bond in orthonitrate indicates that pπ–dπ bonding is likely not the most important explanation for the bond lengths of these heavier anions either.[2] (See the article on hypervalence for a discussion of bonding models)

When orthonitrate is hydrogenated under special conditions, it forms the unknown azorate ion.

Azorate is the deprotonated version of orthonitric acid.

NO4 + H2 → H2NO4

2H3NO4 + O2 → 2H2NO4 + H2O (This formula is more likely to produce nitric acid instead of azorate)

Other nitrogen oxyanions


  1. ^ a b Jansen, Martin (August 1977). "Detection of an Orthonitrate by Vibrational Spectroscopy: Na3NO4". Angewandte Chemie International Edition in English. 16 (8): 534–535. doi:10.1002/anie.197705341.
  2. ^ a b Jansen, Martin (1979-08-31). "Crystal Structure of Na3NO4". Angewandte Chemie International Edition in English. 18 (9): 698–699. doi:10.1002/anie.197906982.
  3. ^ Quesada Cabrera, R.; Sella, A.; Bailey, E.; Leynaud, O.; McMillan, P.F. (April 2011). "High-pressure synthesis and structural behavior of sodium orthonitrate Na3NO4" (PDF). Journal of Solid State Chemistry. 184 (4): 915–920. Bibcode:2011JSSCh.184..915Q. doi:10.1016/j.jssc.2011.02.013.
  4. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.