Orthonitrate

Orthonitrate is a tetrahedral oxoanion of nitrogen with the formula NO3−
4. 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), 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]
Orthonitrate
Names
IUPAC name
Orthonitrate
Identifiers
3D model (JSmol)
Properties
NO3−
4
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).
Infobox references

The resulting orthonitrates are white solids which are extremely sensitive to moisture and CO2, decomposing within minutes to sodium hydroxide, sodium carbonate, and sodium nitrate upon exposure to air.[1]

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

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 oxoanions containing third-row elements like PO43− and SO42−, 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)

Other nitrogen oxoanions

References
  1. 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. 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. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
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