Editing Neptunium (section)

===Other inorganic===
;Hydrides
Neptunium reacts with [[hydrogen]] in a similar manner to its neighbor plutonium, forming the [[hydride]]s NpH<sub>2+''x''</sub> ([[face-centered cubic]]) and NpH<sub>3</sub> ([[hexagonal crystal system|hexagonal]]). These are [[isostructural]] with the corresponding plutonium hydrides, although unlike PuH<sub>2+''x''</sub>, the [[lattice parameter]]s of NpH<sub>2+''x''</sub> become greater as the hydrogen content (''x'') increases. The hydrides require extreme care in handling as they decompose in a vacuum at 300&nbsp;°C to form finely divided neptunium metal, which is [[pyrophoric]].<ref name="Yoshida722">Yoshida et al., pp. 722–4.</ref>

;Phosphates, sulfates, and carbonates
Being chemically stable, neptunium [[phosphate]]s have been investigated for potential use in immobilizing nuclear waste. Neptunium pyrophosphate (α-NpP<sub>2</sub>O<sub>7</sub>), a green solid, has been produced in the reaction between neptunium dioxide and [[boron phosphate]] at 1100&nbsp;°C, though neptunium(IV) phosphate has so far remained elusive. The series of compounds NpM<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>, where M is an [[alkali metal]] ([[lithium|Li]], [[sodium|Na]], [[potassium|K]], [[rubidium|Rb]], or [[caesium|Cs]]), are all known. Some neptunium [[sulfate]]s have been characterized, both aqueous and solid and at various oxidation states of neptunium (IV through VI have been observed). Additionally, neptunium [[carbonate]]s have been investigated to achieve a better understanding of the behavior of neptunium in [[geological repository|geological repositories]] and the environment, where it may come into contact with carbonate and [[bicarbonate]] aqueous solutions and form soluble complexes.<ref>Lemire et al., pp. 177–180.</ref><ref name="Yoshida744">Yoshida et al., pp. 744–5.</ref>