Tin(II) fluoride

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Tin(II) fluoride
Kristallstruktur Zinn(II)-fluorid.png
     Sn2+;      F
Identifiers
CAS number 7783-47-3 YesY
PubChem 24550
UN number 3288
RTECS number XQ3450000
ATC code A01AA04
Jmol-3D images Image 1
Properties
Molecular formula 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)
Solubility in water 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
Crystal structure Monoclinic, mS48
Space group C2/c, No. 15
Hazards
MSDS ICSC 0860
EU Index Not listed
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
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 noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Tin(II) fluoride, commonly referred to commercially (with tin(II) in Latin) as stannous fluoride,[1][2] is a chemical compound with the formula SnF2. It is a colorless solid used as an ingredient in toothpastes that are typically more expensive than those that use sodium fluoride. Stannous fluoride converts the calcium mineral apatite into fluorapatite, which makes tooth enamel more resistant to bacteria-generated acid attacks. In toothpastes containing calcium minerals, sodium fluoride becomes ineffective over time, while stannous fluoride remains effective in strengthening tooth enamel.[3] Stannous fluoride has been shown to be more effective than sodium fluoride in reducing the incidence of dental caries[4] and controlling gingivitis.[5]

Stannous fluoride is used under the trade name "Fluoristan" in the original formulation of the toothpaste Crest, though it was later replaced with sodium monofluorophosphate, or "Fluoristat." It 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. Any stannous fluoride staining that occurs due to improper brushing is not permanent. Stannous fluoride is also used in Oral-B Pro-Expert.[6]

Stannous fluoride is also readily available in over-the-counter rinses.

SnF2 can be prepared by evaporating a solution of SnO in 40% HF.[7]

Aqueous solutions[edit]

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+.[8] Aqueous solutions readily oxidise to form insoluble precipitates of SnIV, which are ineffective as a dental prophylactic.[9] Studies of the oxidation using Mössbauer spectroscopy on frozen samples suggests that O2 is the oxidizing species.[10]

Lewis acidity[edit]

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,[11] and a 1:1 complex with dimethylsulfoxide, (CH3)2SO.SnF2.[12]
In solutions containing the fluoride ion, F, it forms the fluoride complexes SnF3, Sn2F5, and SnF2(OH2).[13] 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.[7] The compound NaSnF3, containing the pyramidal SnF3 anion, can be produced from a pyridine – water solution.[14] Other compounds containing the pyramidal SnF3 anion are known, such as Ca(SnF3)2. [15]

Reducing properties[edit]

SnF2 is a reducing agent, with a standard reduction potential of Eo (SnIV/ SnII) = +0.15V.[16] 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).[7]

Structure[edit]

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.[17] Other forms reported have the GeF2 and paratellurite structures.[17]

Molecular SnF2[edit]

In the vapour phase, SnF2 forms monomers, dimers, and trimers.[13] Monomeric SnF2 is a non-linear molecule with an Sn-F bond length of 206 pm.[13]
Complexes of SnF2, sometimes called difluorostannylene, with an alkyne and aromatic compounds deposited in an argon matrix at 12 K have been reported.[18][19]

Safety[edit]

SnF2 can cause redness and irritation if inhaled or comes in contact with the eyes. At acute levels (over 2mg/m3), if ingested, it can cause abdominal pains and shock.[20]

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 which can be removed by brushing.[21]

References[edit]

  1. ^ "Treato results for Stannous Fluoride and Toothpaste". http://Treato.com/. Treato Ltd. Retrieved 16 June 2013. 
  2. ^ "Latin Names Variable Charge Metals". http://nobel.scas.bcit.ca/. British Columbia Institute of Technology Chemistry Department. Retrieved 16 June 2013. 
  3. ^ 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. 
  4. ^ 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. 
  5. ^ 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. 
  6. ^ 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. 
  7. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  8. ^ 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. 
  9. ^ 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
  10. ^ 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. 
  11. ^ Chung Chun Hsu and R. A. Geanangel (1977). "Synthesis and studies of trimethylamine adducts with tin(II) halides". Inorg. Chem. 16 (1): 2529–2534. doi:10.1021/ic50176a022. 
  12. ^ Chung Chun Hsu and R. A. Geanangel (1980). "Donor and acceptor behavior of divalent tin compounds". Inorg. Chem. 19 (1): 110–119. doi:10.1021/ic50203a024. 
  13. ^ a b c Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
  14. ^ 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. 
  15. ^ 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. 
  16. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. ISBN 978-0130399137. 
  17. ^ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  18. ^ 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 Volume 43 (1): 47–49. doi:10.1007/BF00699133. 
  19. ^ 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. 
  20. ^ "Stannous fluoride (ICSC: 0860)". CDC: International Chemical Safety Cards. Retrieved March 11, 2014. 
  21. ^ "Stannous Fluoride-Dental". WebMD. Retrieved March 11, 2014.