Phosphorus selenide
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some are similar to their phosphorus analogues, the phosphorus sulfides, there are some new forms, molecular PSe and the polymeric "catena"-[PSe]. There is also some doubt about the existence of molecular PSe. Crystallographically confirmed compounds. PSe. Molecular PSe has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units, (-Se-Se-), (analogous to disulfide ) and one selenide unit(-Se-). It was isolated by solvent (CS) extraction from a PSe amorphous phase made from the elements. PSe. PSe has been characterised crystallographically and has the same structure as the low temperature form of PS. It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin. PSe. The PSe molecule has the same structure as PS. It was prepared by reacting PSe with bromine in CS. Section::::"catena"-[PSe]. This compound consists of polymeric chains of norbornane-like units joined by Se atoms. As each P atom in the repeat unit is bonded to  another P atom and to two Se atoms, each P atom has a formal oxidation state of +2. Compounds confirmed spectroscopically. PSe. PSehas two crystalline forms α-PSe with the same molecular structure as α-PS and β-PSe with same molecular structure as β-PS. A fully characterised compound (CuI)PSe contains PSe with a β-PS structure. PSe. This has been reported to have the same structure as PS. One well-known textbook does not mention it at all. PSe. Molecular PSe has been reported to share the same structure as PS and PO, but one well-known textbook  does not mention it at all. A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular PSe. The isoelectronic anion [GeSe] which has the adamantane like PO structure is known, an example is the sodium salt NaGeSe. Other compounds. PSe, PSe, PSe, PSe, PSe, have been reported. Phosphorus - Selenium glasses. Phosphorus -selenium glasses have been examined using P NMR and Raman spectroscopy. Glasses are formed in PSe over the range of compositions 0 < x < 0.8 with a small window around 0.52-0.60 centred on 0.57 (corresponding to the compound PSe) where there is  a tendency to crystallise. For x < 0.47 the glasses contain Se chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond) and P units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular PSe.