Neptunium(V) oxide or neptunium pentoxide is one of two solid oxides of neptunium, the other being neptunium(IV) oxide.https://doi.org/10.1016/j.jct.2016.07.040 It has a chemical formula of Np2O5.
History
Neptunium(V) oxide was first synthesized in 1963 by passing ozone through molten lithium perchlorate containing neptunyl(V) ions and precipitating the product.
Formation
Neptunium(V) oxide can be formed from the calcination of other compounds of neptunium, such as neptunium(VI) oxide (NpO3·xH2O), neptunyl(V) hydroxide (NpO2OH), neptunyl(VI) hydroxide (NpO2(OH)2), or neptunium(V) nitrates (NpO(NO3)3 or NpO2NO3).Lemire, R. J. et al., Chemical Thermodynamics of Neptunium and Plutonium, Elsevier, Amsterdam, 2001.
It can also be formed from the precipitation of neptunyl ions in solution:
Reactions
Neptunium(V) oxide is unstable, and decomposes between 700 and 973 K, forming neptunium(IV) oxide and oxygen gas:
Np2O5 produced from the calcination of neptunyl(VI) hydroxide goes through an intermediate phase Np4O9 before reaching NpO2.
Structure
Neptunium(V) oxide adopts a layered structure. Corresponding neptunium atoms in different layers are bridged by oxygen atoms, forming chains of neptunyl cations. Within each layer, neptunyl cations are linked by oxygen atoms.
The crystal structure of neptunium(V) oxide contains three distinct neptunium sites. Two sites have a coordination geometry of pentagonal bipyramidal, and the other has a coordination geometry of tetragonal bipyramidal.
Neptunium(V) oxide crystals are monoclinic, with space group P2/c, four formula units per unit cell, and unit cell dimensions a=8.17Å, b=6.58Å, c=9.313Å, and β=116.09°. They have a density of 8.18 g/cm3.
Other properties
Neptunium(V) oxide undergoes antiferromagnetic ordering at 22 K.
References