Iodine heptafluoride

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Iodine heptafluoride
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Template:Longitem IF7
Molar mass 259.90 g/mol
Appearance colorless gas
Density 2.6 g/cm3 (6 °C)
2.7 g/cm3 (25 °C)
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Template:Longitem iodine pentafluoride

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Iodine heptafluoride is an interhalogen compound with the chemical formula IF7.[2][3] It has an unusual pentagonal bipyramidal structure, with D5h symmetry, as predicted by VSEPR theory.[4] The molecule can undergo a pseudorotational rearrangement called the Bartell mechanism, which is like the Berry mechanism but for a heptacoordinated system.[5]

Below 4.5 °C, IF7 forms a snow-white powder of colorless crystals, melting at 5-6 °C. However, this melting is difficult to observe, as the liquid form is thermodynamically unstable at 760 mmHg: instead, the compound begins to sublime at 4.77 °C. The dense vapor has a mouldy, acrid odour.[6][7]

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.[8]Template:Sfn 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.

References

  1. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, Template:ISBN
  2. Macintyre, J. E. (Ed.). (1992). Dictionary of Inorganic Compounds (Vol. 3). London: Chapman & Hall.
  3. O'Neil, Maryadele J. (Ed.). (2001). The Merck Index (13th ed.). Whitehouse Station, NJ: Merck.
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  6. Lide, David R. (2011). The CRC Handbook of Chemistry and Physics, 89th ed. p. 4-67.
  7. Script error: No such module "Footnotes".: "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 logp=8,66041602,6T....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 5Template:Nbh6 °C. [From] measurement of the vapor pressure...one arrives at the equation logp=8.66041602.6T....For a pressure of 760 mm it computes a temperature of 4.5 °C.]"
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Common sources

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External links

Template:Iodine compounds Template:Fluorine compounds