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Iodine heptafluoride
Chemical compound

Iodine heptafluoride (IF7) is an interhalogen compound with a unique pentagonal bipyramidal structure exhibiting D5h symmetry, as explained by VSEPR theory. It undergoes a pseudorotational rearrangement known as the Bartell mechanism, analogous to the Berry mechanism for heptacoordinate molecules. Below 4.5 °C, IF7 forms snow-white crystals melting near 5-6 °C; however, the liquid phase is unstable at 760 mmHg, causing it to sublime at 4.77 °C. The vapor is dense with a distinctive mouldy, acrid smell.

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Preparation

IF7 is prepared by passing F2 through liquid IF5 at 90 °C, then heating the vapours to 270 °C. Alternatively, this compound can be prepared from fluorine and dried palladium or potassium iodide to minimize the formation of IOF5, an impurity arising by hydrolysis.78 Iodine heptafluoride is also produced as a by-product when dioxygenyl hexafluoroplatinate is used to prepare other platinum(V) compounds such as potassium hexafluoroplatinate(V), using potassium fluoride in iodine pentafluoride solution:9

2 O2PtF6 + 2 KF + IF5 → 2 KPtF6 + 2 O2 + IF7

Reactions

Iodine heptafluoride decomposes at 200 °C to fluorine gas and iodine pentafluoride.10

Safety considerations

IF7 is highly irritating to both the skin and the mucous membranes. It also is a strong oxidizer and can cause fire on contact with organic material.

Common sources

  • Ruff, Otto; Keim, Rudolf (1930-10-21). "Das Jod-7-fluorid" [Iodine Heptafluoride]. Zeitschrift für anorganische und allgemeine Chemie (in German). 193 (1/2): 176–186. doi:10.1002/zaac.19301930117. ISSN 0863-1786.

References

  1. Macintyre, J. E. (Ed.). (1992). Dictionary of Inorganic Compounds (Vol. 3). London: Chapman & Hall. ↩

  2. O'Neil, Maryadele J. (Ed.). (2001). The Merck Index (13th ed.). Whitehouse Station, NJ: Merck. ↩

  3. K. O. Christe; E. C. Curtis; D. A. Dixon (1993). "On the problem of heptacoordination: vibrational spectra, structure, and fluxionality of iodine heptafluoride". Journal of the American Chemical Society. 115 (4): 1520–1526. doi:10.1021/ja00057a044. /wiki/Journal_of_the_American_Chemical_Society ↩

  4. W. J. Adams; H. Bradford Thompson; L. S. Bartell (1970). "Structure, Pseudorotation, and Vibrational Mode Coupling in IF7: An Electron Diffraction Study" (PDF). Journal of Chemical Physics. 53 (10): 4040–4046. Bibcode:1970JChPh..53.4040A. doi:10.1063/1.1673876. hdl:2027.42/71219. https://deepblue.lib.umich.edu/bitstream/2027.42/71219/2/JCPSA6-53-10-4040-1.pdf ↩

  5. Lide, David R. (2011). The CRC Handbook of Chemistry and Physics, 89th ed. p. 4-67. /wiki/The_CRC_Handbook_of_Chemistry_and_Physics ↩

  6. Ruff & Keim 1930, pp. 180–182: "Das reine Jod-7-fluorid ist bei Zimmer­temperatur ein farbloses Gas, das an der Luft infolge seiner Umsetzung mit dem Wasser­dampf Nebel bildet und muffig sauer riecht. Beim Abkühlen wird es je nach den Versuchs­bedingungen als leicht bewegliche, farblose Flüssigkeit als schneeweißes lockeres Pulver oder in Form farbloser Kristalle erhalten....Die Schmelz­temperatur wurde durch Eintauchen von Proben, die in Quarzröhrchen eingeschmolzen waren, in Bäder passender Temperatur ermittelt und zu 5 bis 6° C gefunden. [Durch] Messung der Dampfdrucke...gelangt man zu der Gleichung log ⁡ p = 8 , 6604 − 1602 , 6 T {\displaystyle \log p=8,6604-{\frac {1602,6}{T}}} ....Für den Druck von 760 mm errechnet sich eine Temperatur von 4,5° C. [Pure iodine heptafluoride is at room temperature a colorless gas, which forms a fog in air on account of its reaction with the humidity and smells musty and acrid. When cooled, it takes the form, depending on experimental conditions, of a free-flowing colorless liquid, a loose snow-white powder, or colorless crystals....The melting point was measured by immersion of a probe in a bath of the right temperature, which was melting in a little quartz tube and found to be 5‑6 °C. [From] measurement of the vapor pressure...one arrives at the equation log ⁡ p = 8.6604 − 1602.6 T {\displaystyle \log p=8.6604-{\frac {1602.6}{T}}} ....For a pressure of 760 mm it computes a temperature of 4.5 °C.]" - Ruff, Otto; Keim, Rudolf (1930-10-21). "Das Jod-7-fluorid" [Iodine Heptafluoride]. Zeitschrift für anorganische und allgemeine Chemie (in German). 193 (1/2): 176–186. doi:10.1002/zaac.19301930117. ISSN 0863-1786. https://doi.org/10.1002%2Fzaac.19301930117 ↩

  7. Schumb, W. C.; Lynch, M. A. (1950). "Iodine Heptafluoride". Industrial & Engineering Chemistry. 42 (7): 1383–1386. doi:10.1021/ie50487a035. /wiki/Industrial_%26_Engineering_Chemistry ↩

  8. Ruff & Keim 1930. - Ruff, Otto; Keim, Rudolf (1930-10-21). "Das Jod-7-fluorid" [Iodine Heptafluoride]. Zeitschrift für anorganische und allgemeine Chemie (in German). 193 (1/2): 176–186. doi:10.1002/zaac.19301930117. ISSN 0863-1786. https://doi.org/10.1002%2Fzaac.19301930117 ↩

  9. Beveridge, A. D.; Clark, H. C. (1967). "Pentahalides of the Transition Metals". In Gutmann, Viktor (ed.). Halogen Chemistry. Vol. 3. Academic Press. pp. 179–226. ISBN 9780323148474. 9780323148474 ↩

  10. Кнунянц, И. Л. (1990). Химическая энциклопедия : в пяти томах (in Russian). Советская Энциклопедия. p. 496. ISBN 5-85270-008-8. OCLC 19556260. 5-85270-008-8 ↩