Calcium fluoride is theinorganic compound of the elementscalcium andfluorine with theformula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineralfluorite (also called fluorspar), which is often deeply coloured owing to impurities.
The compound crystallizes in a cubic motif called thefluorite structure.
Unit cell of CaF2, known as fluorite structure, from two equivalent perspectives. The second origin is often used when visualising point defects centred on the cation.[4]
Ca2+ centres are eight-coordinate, being centred in a cube of eight F− centres. Each F− centre is coordinated to four Ca2+ centres in the shape of a tetrahedron.[5] Although perfectly packed crystalline samples are colorless, the mineral is often deeply colored due to the presence ofF-centers.The same crystal structure is found in numerous ionic compounds with formula AB2, such asCeO2,cubic ZrO2,UO2,ThO2, andPuO2. In the correspondinganti-structure, called the antifluorite structure, anions and cations are swapped, such asBe2C.
The gas phase is noteworthy for failing the predictions ofVSEPR theory; theCaF2 molecule is not linear likeMgF2, but bent with abond angle of approximately 145°; the strontium and barium dihalides also have a bent geometry.[6] It has been proposed that this is due to the fluorideligands interacting with the electron core[7][8] or the d-subshell[9] of the calcium atom.
Naturally occurring mineral fluorite(CaF2)is the principal source ofhydrogen fluoride, a commodity chemical used to produce a wide range of materials. Calcium fluoride in thefluorite state is of significant commercial importance as a fluoride source.[10] Hydrogen fluoride is liberated from the mineral by the action of concentratedsulfuric acid:[11][12]
Separately, calcium fluoride can be generated as a waste product via ion exchange ofPFAS rich water using a durable layered double hydroxide(LDH) membrane of copper and aluminum heated to 500C.[14][15]
Lenses and Windows: Calcium fluoride is transparent over a broad range from ultraviolet (UV) to infrared (IR) frequencies. Its low refractive index reduces the need foranti-reflection coatings. Its insolubility in water is convenient as well.[citation needed] It also allows much smaller wavelengths to pass through.[citation needed] Calcium fluoride is used to manufacture optical components such as windows and lenses used in:
Pesticides and Fungicides: Used in formulations to stabilize products and protect crops.
Certain well-categorized molecular calcium fluorides can serve as reagents for nucleophilic fluoride addition to organic compounds.[17][18] Well-characterized molecular calcium fluorides are clusters are formed by treating CaF2 with large, multidentate ligands.[19]
CaF2 is classified as "not dangerous", although reacting it withsulfuric acid produceshydrofluoric acid, which is highly corrosive and toxic. With regards to inhalation, theNIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air.[13]
^Pradyot Patnaik.Handbook of Inorganic Chemicals. McGraw-Hill, 2002,ISBN0-07-049439-8.
^X-ray Diffraction Investigations of CaF2 at High Pressure, L. Gerward, J. S. Olsen, S. Steenstrup, M. Malinowski, S. Åsbrink and A. Waskowska, Journal of Applied Crystallography (1992), 25, 578–581,doi:10.1107/S0021889892004096.
^Bytheway, I.; Gillespie, R. J.; Tang, T. H.; Bader, R.F (1995). "Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba".Inorg. Chem.34 (9):2407–2414.doi:10.1021/ic00113a023.
