Phosphorus pentafluoride
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| General | |||||||||||||||||||
| Surname | Phosphorus pentafluoride | ||||||||||||||||||
| other names |
Phosphorus (V) fluoride |
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| Molecular formula | PF 5 | ||||||||||||||||||
| Brief description |
colorless gas with a pungent odor, heavier than air |
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| properties | |||||||||||||||||||
| Molar mass | 125.97 g mol −1 | ||||||||||||||||||
| Physical state |
gaseous |
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| density |
5.69 kg m −3 at 0 ° C, 1013 mbar |
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| Melting point |
−93.8 ° C |
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| boiling point |
−84.6 ° C |
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| Vapor pressure |
2.79 M Pa (20 ° C) |
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| solubility |
decomposes by hydrolysis in water |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
Phosphorus pentafluoride (phosphorus (V) fluoride) is an inorganic , chemical compound made up of the elements phosphorus and fluorine with the empirical formula PF 5 and belongs to the compound class of phosphorus halides. Under standard conditions it is a colorless, very toxic and non-flammable gas with a pungent odor. In moist air or dissolved in water, it reacts violently with the formation of hydrogen fluoride HF and phosphoric acid H 3 PO 4 .
history
Phosphorus pentafluoride was discovered in 1876 by the British chemist Thomas Edward Thorpe (1845-1925) and described for the first time.
Extraction and presentation
Phosphorus pentafluoride can be prepared by fluorination of phosphorous pentachloride PCl 5 with the aid of arsenic trifluoride AsF 3 to form arsenic trichloride AsCl 3 are shown.
The phosphorus pentafluoride escapes as a heavily fuming gas, while the arsenic trichloride remains.
properties
Physical Properties
Phosphorus pentafluoride molecules have a trigonal-bipyramidal structure, with the phosphorus atom in the center and the covalently bonded fluorine atoms in the triangular base (equatorial positions) and at the two tips (axial or apical positions) of the bipyramid. The F − P – F bond angles in the base are 120 °, while the bonds to both apical fluorine atoms are perpendicular to the base. The bond lengths between phosphorus and the equatorial fluorine atoms are each 153 pm and are 5 pm shorter than to the two atoms in the apical position (158 pm).
Although the geometry of the trigonal bipyramid would have to distinguish two types of fluorine atoms, measurements with 19 F - NMR spectroscopy only yield a single signal for the fluorine atoms instead of the expected two. This is caused by the Berry pseudorotation , in which the fluorine atoms constantly change their positions within the molecule. This change takes place faster than the measuring device can record and a time-averaged structure with apparently five equivalent fluorine atoms is shown in the spectra.
Under standard conditions, phosphorus pentafluoride is a colorless gas and about 4.5 times as heavy as air.
Below the melting point of −93.8 ° C, phosphorus pentafluoride crystallizes in the hexagonal crystal system in the space group P 6 3 / mmc (space group number 194) with the lattice parameters a = 556 pm and c = 618 pm ( c / a = 1.11 ) as well as two formula units per unit cell .
Chemical properties
Phosphorus pentafluoride is extremely susceptible to hydrolysis . In moist air or generally in contact with water, it decomposes spontaneously in a violent reaction with the formation of hydrogen fluoride HF and phosphoric acid H 3 PO 4 .
In solutions with high fluoride ion concentrations, phosphorus pentafluoride reacts as a Lewis acid to form the hexafluorophosphate (V) anion PF 6 - , which is isoelectronic to the sulfur hexafluoride SF 6 and the hexafluorosilicate (IV) anion SiF 6 2− . The underlying hexafluorophosphoric acid HPF 6 , analogously to the hexafluorosilicic acid H 2 SiF 6 , cannot be isolated in pure form by dehydration, but breaks down again to PF 5 with elimination of HF .
By splitting off HF on contact with water, phosphorus pentafluoride etches glass surfaces.
There are derivatives of phosphorus pentafluoride in the form of the fluorophosphines HPF 4 , H 2 PF 3 and H 3 PF 2 , the hydrogen atoms replacing fluorine atoms in equatorial positions.
literature
- AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 780.
- TE Thorpe: About phosphorus pentafluoride . In: Justus Liebig's Annals of Chemistry . Vol. 182, No. 1-2, 1876, pp. 201-206. ISSN 0075-4617
Individual evidence
- ↑ a b c d e f g Entry on phosphorus pentafluoride in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
- ↑ TE Thorpe: On Phosphorus Pentafluoride . In: Proceedings of the Royal Society of London . Vol. 25, 1876, pp. 122-123.
- ↑ D. Mootz, M. Wiebcke: Fluorides and fluoro acids. XIII. The crystal structure of phosphorus pentafluoride . In: Journal of Inorganic and General Chemistry . Vol. 545, No. 2, 1987, pp. 39-42. ISSN 0044-2313 .
