Difluoride

Not to be confused with Bifluoride.

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

Order and disorder in difluorides
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.

• Beryllium difluoride
• Magnesium fluoride
• Calcium fluoride
• Strontium difluoride
• Barium fluoride
• Radium fluoride

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

• Neodymium difluoride^{[citation needed]}
• Samarium difluoride^[5]
• Europium difluoride^[5]
• Dysprosium difluoride^{[citation needed]}
• Thulium difluoride^[5]
• Ytterbium difluoride^[6][5]

Transition metal difluorides

Compounds of the form MF₂:

• Cadmium difluoride
• Chromium(II) fluoride
• Cobalt difluoride
• Copper(II) fluoride
• Iron(II) fluoride
• Manganese(II) fluoride
• Mercury difluoride
• Nickel difluoride
• Palladium difluoride
• Platinum difluoride
• Silver difluoride
• Vanadium difluoride
• Zinc difluoride

Post-transition metal difluorides

• Lead difluoride
• Tin(II) fluoride

Nonmetal and metalloid difluorides

• Dinitrogen difluoride
• Oxygen difluoride
• Dioxygen difluoride
• Selenoyl difluoride
• Sulfur difluoride
• Disulfur difluoride
• Thionyl difluoride
• Germanium difluoride

Noble gas difluorides

• Helium difluoride (hypothetical) ^[7]
• Argon difluoride (predicted)
• Krypton difluoride
• Xenon difluoride
• Radon difluoride

Bifluorides

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

• Ammonium bifluoride
• Potassium bifluoride
• Sodium bifluoride

Organic difluorides

• Ethanedioyl difluoride
• Ethylidene difluoride
• Carbonyl difluoride
• Carbon dibromide difluoride (dibromodifluoromethane)
• Carbon dichloride difluoride (dichlorodifluormethane)
• Methyl difluoride
• Methylphosphonyl difluoride
• Polyvinylidene difluoride