Neptunium tetrabromide

Neptunium tetrabromide is a binary inorganic compound of neptunium metal and bromine with the chemical formula NpBr4.

Synthesis
The compound can be prepared from the reaction of bromine with metallic neptunium:


 * Np + 2Br2 -> NpBr4

Also, a reaction of aluminum bromide with neptunium(IV) oxide:


 * 3NpO2 + 4AlBr3 -> 3NpBr4 + 2Al2O3

Physical properties
Neptunium tetrabromide forms red-brown hygroscopic crystals of monoclinic crystal system, spatial group P 2/c, cell parameters a = 1.089 nm, b = 0.874 nm, c = 0.705 nm, β = 95.19°, Z = 4.

NpBr4 is easily purified by sublimation in a vacuum.

Chemical properties
Decomposes under strong heating to form neptunium tribromide:


 * 2NpBr4 -> 2NpBr3 + Br2

With careful oxidation with antimony(III) oxide, the compound forms neptunium oxidibromide:


 * NpBr4 + Sb2O3 -> NpOBr2 + 2SbOBr