Phosphorus Pentachloride - Structure

Structure

The structures for the phosphorus chlorides are invariably consistent with VSEPR theory. The structure of PCl5 depends on its environment. Gaseous and molten PCl5 is a neutral molecule with trigonal bipyramidal (D3h) symmetry. The hypervalent nature of this species (as well as for PCl−
6, see below) can be explained with three-center four-electron bonding model. This trigonal bipyramidal structure persists in non-polar solvents, such as CS2 and CCl4. In the solid state PCl5 is ionic, formulated PCl+
4PCl−
6.

In solutions of polar solvents, PCl5 undergoes "autoionization". Dilute solutions dissociate according to the following equilibrium:

PCl5 [PCl+
4]Cl−

At higher concentrations, a second equilibrium becomes more important:

2 PCl5 [PCl+
4]

The cation PCl+
4 and the anion PCl−
6 are tetrahedral and octahedral, respectively. At one time, PCl5 in solution was thought to form a dimeric structure, P2Cl10, but this suggestion is not supported by Raman spectroscopic measurements.

AsCl5 and SbCl5 also adopt trigonal bipyramidal structures. The relevant bond distances are 211 (As-Cleq), 221 (As-Cleq), 227 (Sb-Cleq), and 233.3 pm (Sb-Clax ). At low temperatures, SbCl5 converts to the dimer, bioctahedral Sb2Cl10, structurally related to niobium pentachloride.

Read more about this topic:  Phosphorus Pentachloride

Famous quotes containing the word structure:

    “Each structure and institution here was so primitive that you could at once refer it to its source; but our buildings commonly suggest neither their origin nor their purpose.”
    —Henry David Thoreau (1817–1862)

    “There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.”
    —Donald Davidson (b. 1917)

    “The philosopher believes that the value of his philosophy lies in its totality, in its structure: posterity discovers it in the stones with which he built and with which other structures are subsequently built that are frequently better—and so, in the fact that that structure can be demolished and yet still possess value as material.”
    —Friedrich Nietzsche (1844–1900)