Difluoride

Difluorides are chemical compounds with two fluorine atoms per molecule (or per formula unit).

Not to be confused with Bifluoride.
Order and disorder in difluorides
A parallelogram-shaped outline with space-filling diatomic molecules (joined circles) arranged in two layers cube of 8 yellow atoms with white ones at the holes of the yellow structure
The fluorite structure Beryllium fluoride glass

Metal difluorides are all ionic. Despite being highly ionic, the alkaline earth metal difluorides generally have extremely high lattice stability and are thus insoluble in water. The exception is beryllium difluoride. In addition, many transition metal difluorides are water-soluble.

Calcium difluoride is a notable compound. In the form of the mineral fluorite it is the major source of commercial fluorine. It also has an eponymic crystal structure, which is an end member of the spectrum starting from bixbyite and progressing through pyrochlore.

List of the difluorides

Examples of the difluorides include:

Alkaline earth metal difluorides

The alkaline earth metals all exhibit the oxidation state +2, and form difluorides. The difluoride of radium is however not well established due to the element's high radioactivity.

Solubility-related constants of alkaline earth metal fluorides
Metal
 M2+ HE[1] F− HE[2] "MF2" unit
HE		 MF2 lattice
energies (−kJ/mol)[3]		 Solubility
(mol/L)[4]
Be 2,455 458 3,371 3,526 25
Mg 1,922 458 2,838 2,978 0.0012
Ca 1,577 458 2,493 2,651 0.0002
Sr 1,415 458 2,331 2,513 0.0008
Ba 1,361 458 2,277 2,373 0.006

Lanthanide difluorides

Transition metal difluorides

Compounds of the form MF2:

Post-transition metal difluorides

Nonmetal and metalloid difluorides

Noble gas difluorides

Bifluorides

The bifluorides contain the two fluorine atoms in a covalently bound HF2− polyatomic ion rather than as F− anions.

Organic difluorides

References
  1. Wiberg, Wiberg & Holleman 2001, pp. XXXVI–XXXVII.
  2. Wiberg, Wiberg & Holleman 2001, p. XXXVI.
  3. Lide 2004, p. 12-23.
  4. Wiberg, Wiberg & Holleman 2001, p. 1073.
  5. "Samarium(II) fluoride". Pubchem.ncbi.nlm.nih.gov. Retrieved 22 February 2022.
  6. Elements, American. "Europium(II) Fluoride". Americanelements.com. Retrieved 22 February 2022.
  7. "EUROPIUM(II) FLUORIDE | 14077-39-5". Chemicalbook.com. Retrieved 22 February 2022.
  8. Georg Brauer: Handbuch der Präparativen Anorganischen Chemie. 3., umgearb. Auflage. Band I. Enke, Stuttgart 1975, ISBN 3-432-02328-6, p. 255.

Bibliography
  • Greenwood, N. N.; Earnshaw, A. (1998). Chemistry of the Elements (second ed.). Butterworth Heinemann. ISBN 0-7506-3365-4.
  • Lide, David R. (2004). Handbook of chemistry and physics (84th ed.). CRC Press. ISBN 0-8493-0566-7.
  • Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. ISBN 978-0-12-352651-9. Retrieved 3 March 2011.
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