Tin(II) fluoride

Tin(II) fluoride, commonly referred to commercially as stannous fluoride[1][2] (from Latin stannum, 'tin'), is a chemical compound with the formula SnF2. It is a colourless solid used as an ingredient in toothpastes.

Tin(II) fluoride

     Sn2+;      F−
Names
IUPAC name
Tin(II) fluoride
Other names
Stannous fluoride
Identifiers
3D model (JSmol)
ECHA InfoCard 100.029.090
RTECS number
  • XQ3450000
UNII
UN number 3288
Properties
SnF2
Molar mass 156.69 g/mol
Appearance colorless solid
Density 4.57 g/cm3
Melting point 213 °C (415 °F; 486 K)
Boiling point 850 °C (1,560 °F; 1,120 K)
31 g/100 mL (0 °C);
35 g/100 mL (20 °C);
78.5 g.100 mL (106 °C)
Solubility soluble in KOH, KF;
negligible in ethanol, ether, chloroform
Structure
Monoclinic, mS48
C2/c, No. 15
Pharmacology
A01AA04 (WHO)
Hazards
Safety data sheet ICSC 0860
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
2
0
Flash point Non-flammable
Related compounds
Other anions
 Tin(II) chloride,
Tin(II) bromide,
Tin(II) iodide
Other cations
 Germanium tetrafluoride,
Tin tetrafluoride,
Lead(II) fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Cavity prevention

Stannous fluoride was introduced as an alternative to sodium fluoride for the prevention of cavities. It was introduced for this purpose by Joseph Muhler and William Nebergall. In recognition for their innovation, these two individuals were inducted into the Inventor's Hall of Fame.[1]

Stannous fluoride converts the calcium mineral apatite into fluorapatite, which makes tooth enamel more resistant to bacteria-generated acid attacks.[3] The majority of toothpastes contain calcium minerals; over time these react with sodium fluoride to form calcium fluoride, which is almost completely insoluble and thus ineffective for tooth protection. Stannous fluoride is a more stable ingredient and thus remains effective in strengthening tooth enamel upon longer storage.[4] Stannous fluoride has been shown to be as effective as sodium fluoride in reducing the incidence of dental caries[5] and controlling gingivitis.[6]

Stannous fluoride was used under the trade name Fluoristan in the original formulation of the toothpaste brand Crest, though it was later replaced with sodium monofluorophosphate under the trade name Fluoristat. Stannous fluoride is the active ingredient in Crest Pro Health brand toothpaste. Crest Pro Health issues a warning on the tube that stannous fluoride may cause staining, which can be avoided by proper brushing, and that its particular formulation is resistant to staining. However, any stannous fluoride staining that occurs due to improper brushing is not permanent. Stannous fluoride is also used in Oral-B Pro-Expert.[7] Stannous fluoride is also readily available in over-the-counter rinses.

Production

SnF2 can be prepared by evaporating a solution of SnO in 40% HF.[8]

SnO + 2 HF → SnF2 + H2O

Aqueous solutions

Readily soluble in water, SnF2 is hydrolysed. At low concentration, it forms species such as SnOH+, Sn(OH)2 and Sn(OH)3−. At higher concentrations, predominantly polynuclear species are formed, including Sn2(OH)22+ and Sn3(OH)42+.[9] Aqueous solutions readily oxidise to form insoluble precipitates of SnIV, which are ineffective as a dental prophylactic.[10] Studies of the oxidation using Mössbauer spectroscopy on frozen samples suggests that O2 is the oxidizing species.[11]

Lewis acidity

SnF2 acts as a Lewis acid. For example, it forms a 1:1 complex (CH3)3NSnF2 and 2:1 complex [(CH3)3N]2SnF2 with trimethylamine,[12] and a 1:1 complex with dimethylsulfoxide, (CH3)2SO·SnF2.[13]
In solutions containing the fluoride ion, F−, it forms the fluoride complexes SnF3−, Sn2F5−, and SnF2(OH2).[14] Crystallization from an aqueous solution containing NaF produces compounds containing polynuclear anions, e.g. NaSn2F5 or Na4Sn3F10 depending on the reaction conditions, rather than NaSnF3.[8] The compound NaSnF3, containing the pyramidal SnF3− anion, can be produced from a pyridine–water solution.[15] Other compounds containing the pyramidal SnF3− anion are known, such as Ca(SnF3)2.[16]

Reducing properties

SnF2 is a reducing agent, with a standard reduction potential of Eo (SnIV/ SnII) = +0.15 V.[17] Solutions in HF are readily oxidised by a range of oxidizing agents (O2, SO2 or F2) to form the mixed-valence compound Sn3F8 (containing SnII and SnIV and no Sn–Sn bonds).[8]

Structure

The monoclinic form contains tetramers, Sn4F8, where there are two distinct coordination environments for the Sn atoms. In each case, there are three nearest neighbours, with Sn at the apex of a trigonal pyramid, and the lone pair of electrons sterically active.[18] Other forms reported have the GeF2 and paratellurite structures.[18]

Molecular SnF2

In the vapour phase, SnF2 forms monomers, dimers, and trimers.[14] Monomeric SnF2 is a non-linear molecule with an Sn−F bond length of 206 pm.[14] Complexes of SnF2, sometimes called difluorostannylene, with an alkyne and aromatic compounds deposited in an argon matrix at 12 K have been reported.[19][20]

Safety

SnF2 can cause redness and irritation if inhaled or comes into contact with the eyes. At acute levels (over 2 mg/m3), if ingested, it can cause abdominal pains and shock.[21] Rare but serious allergic reactions are possible (symptoms include itching, swelling, and difficulty breathing). When used in dental products, mild tooth discoloration may also occur; this can be removed by brushing.[22]

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References
  1. "National Inventors Hall of Fame Announces 2019 Inductees at CES". National Inventors Hall of Fame. Retrieved 6 February 2019.
  2. "Latin Names Variable Charge Metals". Nobel.SCAS.BCIT.ca/. British Columbia Institute of Technology Chemistry Department. Retrieved 16 June 2013.
  3. Groeneveld, A.; Purdell-Lewis, D. J.; Arends, J. (1976). "Remineralization of artificial caries lesions by stannous fluoride". Caries Research. 10 (3): 189–200. doi:10.1159/000260201. ISSN 0008-6568. PMID 1063601.
  4. Hattab, F. (April 1989). "The State of Fluorides in Toothpastes". Journal of Dentistry. 17 (2): 47–54. doi:10.1016/0300-5712(89)90129-2. PMID 2732364.
  5. Nevitt GA, Witter DH, Bowman WD (September 1958). "Topical applications of sodium fluoride and stannous fluoride". Public Health Rep. 73 (9): 847–50. doi:10.2307/4590256. JSTOR 4590256. PMC 1951625. PMID 13579125.
  6. Perlich, MA; Bacca, LA; Bollmer, BW; Lanzalaco, AC; McClanahan, SF; Sewak, LK; Beiswanger, BB; Eichold, WA; et al. (1995). "The clinical effect of a stabilized stannous fluoride dentifrice on plaque formation, gingivitis and gingival bleeding: a six-month study". The Journal of Clinical Dentistry. 6 (Special Issue): 54–58. PMID 8593194.
  7. Lippert F, Newby EE, Lynch RJ, Chauhan VK, Schemehorn BR (2009). "Laboratory assessment of the anticaries potential of a new dentifrice". J Clin Dent. 20 (2): 45–9. PMID 19591336.
  8. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  9. Séby F., Potin-Gautier M., Giffaut E., Donard O. F. X.; Potin-Gautier; Giffaut; Donard (2001). "A critical review of thermodynamic data for inorganic tin species". Geochimica et Cosmochimica Acta. 65 (18): 3041–3053. Bibcode:2001GeCoA..65.3041S. doi:10.1016/S0016-7037(01)00645-7.CS1 maint: multiple names: authors list (link)
  10. David B. Troy, 2005, Remington: The Science and Practice of Pharmacy, Lippincott Williams & Wilkins, ISBN 0-7817-4673-6, ISBN 978-0-7817-4673-1
  11. Denes G; Lazanas G.; Lazanas (1994). "Oxidation of SnF2 stannous fluoride in aqueous solutions". Hyperfine Interactions. 90 (1): 435–439. Bibcode:1994HyInt..90..435D. doi:10.1007/BF02069152.
  12. Chung Chun Hsu & R. A. Geanangel (1977). "Synthesis and studies of trimethylamine adducts with tin(II) halides". Inorg. Chem. 16 (1): 2529–2534. doi:10.1021/ic50176a022.
  13. Chung Chun Hsu & R. A. Geanangel (1980). "Donor and acceptor behavior of divalent tin compounds". Inorg. Chem. 19 (1): 110–119. doi:10.1021/ic50203a024.
  14. Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5.
  15. Salami T. O., Zavalij P. Y. and Oliver S. R. J. (2004). "Synthesis and crystal structure of two tin fluoride materials: NaSnF3 (BING-12) and Sn3F3PO4". Journal of Solid State Chemistry. 177 (3): 800–805. Bibcode:2004JSSCh.177..800S. doi:10.1016/j.jssc.2003.09.013.
  16. Kokunov Y. V.; Detkov D. G.; Gorbunova Yu. E.; Ershova M. M.; Mikhailov Yu. N. (2001). "Synthesis and Crystal Structure of Calcium Trifluorostannate(II)". Doklady Chemistry. 376 (4–6): 52–54. doi:10.1023/A:1018855109716.
  17. Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. ISBN 978-0-13-039913-7.
  18. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  19. S. E. Boganov, V. I. Faustov, M. P. Egorov and O. M. Nefedov (1994). "Matrix IR spectra and quantum chemical studies of the reaction between difluorostannylene and hept-1-yne. The first direct observation of a carbene analog π-complex with alkyne". Russian Chemical Bulletin. 43 (1): 47–49. doi:10.1007/BF00699133.CS1 maint: multiple names: authors list (link)
  20. S. E. Boganov, M. P. Egorov and O. M. Nefedov (1999). "Study of complexation between difluorostannylene and aromatics by matrix IR spectroscopy". Russian Chemical Bulletin. 48 (1): 98–103. doi:10.1007/BF02494408.
  21. "Stannous fluoride (ICSC: 0860)". CDC: International Chemical Safety Cards. Retrieved March 11, 2014.
  22. "Stannous Fluoride-Dental". WebMD. Retrieved March 11, 2014.
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