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Phosphorus pentabromide is a reactive, yellow solid of formula P Br 5, which has the structure [PBr 4] + Br − (tetrabromophosphonium bromide) in the solid state but in the vapor phase is completely dissociated to PBr 3 and Br 2.
Phosphorus pentachloride, phosphorus pentabromide, and phosphorus heptabromide are ionic in the solid and liquid states; PCl 5 is formulated as PCl 4 + PCl 6 –, but in contrast, PBr 5 is formulated as PBr 4 + Br −, and PBr 7 is formulated as PBr 4 + Br 3 −. They are widely used as chlorinating and brominating agents in organic chemistry.
Phosphorus pentafluoride is a Lewis acid.This property is relevant to its ready hydrolysis. A well studied adduct is PF 5 with pyridine.With primary and secondary amines, the adducts convert readily to dimeric amido-bridged derivatives with the formula [PF 4 (NR 2)] 2.
[1] [2] [3] Introduced by Gilbert N. Lewis in his 1916 article The Atom and the Molecule, a Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. [4] Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.
Phosphoryl bromide is prepared by the reaction between phosphorus pentabromide and phosphorus pentoxide: [4] [5]. 3 PBr 5 + P 2 O 5 → 5 POBr 3. It can also be prepared via the slow addition of liquid bromine to phosphorus tribromide at 0 °C, followed by the slow addition of water and vacuum distillation of the resulting slurry.
Phosphorus tribromide, like PCl 3 and PF 3, has both properties of a Lewis base and a Lewis acid. For example, with a Lewis acid such as boron tribromide it forms stable 1 :1 adducts such as Br 3 B · PBr 3. At the same time PBr 3 can react as an electrophile or Lewis acid in many of its reactions, for example with amines.
The structures for the phosphorus chlorides are invariably consistent with VSEPR theory. The structure of PCl 5 depends on its environment. Gaseous and molten PCl 5 is a neutral molecule with trigonal bipyramidal geometry and (D 3h) symmetry. The hypervalent nature of this species (as well as of PCl −
The structure of a typical phosphorane group. A phosphorane (IUPAC name: λ 5-phosphane) is a functional group in organophosphorus chemistry with pentavalent phosphorus. Phosphoranes have the general formula PR 5. Phosphoranes of the type PX 5 adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three ...