Neptunium(V) oxide

Neptunium(V) oxide or neptunium pentoxide is one of two stable oxides of neptunium, the other being neptunium(IV) oxide.^[3] It has a chemical formula of Np₂O₅.^[1]

Neptunium(V) oxide

Names
IUPAC name Neptunium(V) oxide
Other names Neptunium pentoxide Dineptunium pentoxide
Identifiers
3D model (JSmol)	Interactive image
InChI InChI=1S/2Np.5O/q2*+5;5*-2 Key: MOPDXFDBEISTFG-UHFFFAOYSA-N
SMILES [Np+5].[Np+5].[O-2].[O-2].[O-2].[O-2].[O-2]
Properties
Chemical formula	Np2O5
Molar mass	554.09 g/mol[1]
Appearance	Green crystals[2]
Density	8.18 g/cm3[2]
Melting point	427 °C; 800 °F; 700 K[3] (decomposes)
Solubility in water	Insoluble[2]
Related compounds
Other anions	Neptunium(V) fluoride
Other cations	Protactinium(V) oxide Uranium(V) oxide
Related neptunium oxides	Neptunium(IV) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

History

Neptunium(V) oxide was first synthesized in 1963 by passing ozone through molten lithium perchlorate containing neptunyl(V) ions and precipitating the product.^[4]

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).^[5][6]

It can also be formed from the precipitation of neptunyl ions in solution:^[2][6]

2NpO+2(aq) + H₂O(l) → Np₂O₅(cr) + H⁺(aq)

Reactions

Neptunium(V) oxide decomposes at 700 K, forming neptunium(IV) oxide and oxygen gas:^[3][5]

Np₂O₅ → 2 NpO₂ + 1/₂ O₂

Np₂O₅ produced from the calcination of neptunyl(VI) hydroxide goes through an intermediate phase Np₄O₉ before reaching NpO₂.^[5]

Structure

A single unit cell of Np₂O₅.

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.^[2]

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.^[2]

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.^[2]

Other properties

Neptunium(V) oxide undergoes antiferromagnetic ordering at 22 K.^[2]