Lead(II) iodide

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Lead(II) iodide
Lead(II) iodide
Lead iodide.jpg
Names
Other names
Plumbous iodide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.220
UNII
Properties
PbI
2
Molar mass 461.01 g/mol
Appearance bright yellow powder
Odor odorless
Density 6.16 g/cm3
Melting point 402 °C (756 °F; 675 K)
Boiling point 953 °C (1,747 °F; 1,226 K)
  • 0.044 g/100 mL (0 °C)
  • 0.0756 g/100 mL (20 °C)[1]
  • 0.41 g/100 mL (100 °C)[2]
4.41 x 10−9 (20 °C)
Solubility
Band gap 2.3 eV
−126.5·10−6 cm3/mol
Structure
Rhombohedral, hexagonal hP3
P-3m1, No. 164
octahedral
Hazards
Repr. Cat. 1/3
Harmful (Xn)
Dangerous for the environment (N)
R-phrases (outdated) R61, R20/22, R33, R62, R50/53
S-phrases (outdated) S53, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas 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
Other cations
Tin(II) iodide
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Lead(II) iodide or lead iodide is a salt with the formula PbI
2
. At room temperature, it is a bright yellow odorless crystalline solid, that becomes orange and red when heated.[4] It was formerly called plumbous iodide.

The compound currently has a few specialized applications, such as the manufacture of solar cells[5] and X-ray and gamma-ray detectors.[6] Its prepraration is a popular demonstration in basic chemistry education, to teach topics such as double displacement reactions and stoichometry.[7] It is decomposed by light at moderately high temperatures[2] and this effect has been used in a patented photographic process.[8]

Lead iodide was formerly employed as a yellow pigment in some paints, with the name iodide yellow. However, that use has been largely discontinued due to its toxicity and poor stability.[9]

Preparation[edit]

PbI
2
is commonly synthesized via a double displacement reaction between potassium iodide KI and lead(II) nitrate Pb(NO
3
)2 in water solution:

Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3

While the potassium nitrate KNO
3
is soluble, the lead iodide PbI
2
is nearly insoluble at room temperature, and thus precipitates out.[10]

Other soluble salts containing lead(II) and iodide can be used instead, for example lead(II) acetate[5] and sodium iodide.

The compound can also be synthesized by reacting iodine vapor with molten lead between 500 and 700 °C.[11]

A thin film of PbI
2
can also be prepared by depositing a film of lead sulfide PbS and exposing it to iodine vapor, by the reaction

PbS + I2 → PbI2 + S

The sulfur is then washed with dimethyl sulfoxide.[12]

Crystallization[edit]

Lead iodide prepared from cold solutions of Pb2+
and I
salts usually consists of many small hexagonal platelets, giving the yellow precipitate a silky appearance. Larger crystals can be obtained by exploiting the fact that solubility of lead iodide in water (like those of lead chloride and lead bromide) increases dramatically with temperature. The compound is colorless when dissolved in hot water, but crystallizes on cooling as thin but visibly larger bright yellow flakes, that settle slowly through the liquid — a visual effect often described as "golden rain".[13] Larger crystals can be obtained by autoclaving the PbI
2
with water under pressure at 200 °C.[14]

Even larger crystals can be obtained by slowing down the common reaction. A simple setup is to submerge two beakers containing the concentrated reactants in a larger container of water, taking care to avoid currents. As the two substances diffuse through the water and meet, they slowly react and deposit the iodide in the space between the beakers.[15]

Another similar method, pioneered by E. Hatschek in the early 20th century,[16] is to react the two substances in a gel medium, that slows down the diffusion and supports the growing crystal away from the container's walls. Patel and Rao have used this method to grow crystals up to 30 mm in diameter and 2 mm thick[17]

The reaction can be slowed also by separating the two reagents with a permeable membrane. This approach, with a cellulose membrane, was used in September 1988 to study the growth of PbI
2
crystals in zero gravity, in an experiment flown on the Space Shuttle Discovery.[18]

PbI
2
can also be crystallized from powder by sublimation at 390 °C, in near vacuum[19] or in a current of argon with some hydrogen.[20]

Large high-purity crystals can be obtained by zone melting or by the Bridgman–Stockbarger technique.[11][19] These processes can remove various impurities from commercial PbI
2
.[21]

Applications[edit]

Lead iodide is a precursor material in the fabrication of highly efficient solar cells. Typically, a solution of PbI
2
in an organic solvent, such as dimethylformamide or dimethylsulfoxide, is applied over a titanium dioxide layer by spin coating. The layer is then treated with a solution of methylammonium iodide CH
3
NH
3
I
and annealed, turning it into the double salt methylammonium lead iodide CH
3
NH
3
PbI
3
, with a perovskite structure. The reaction changes the film's color from yellow to light brown.[5]

PbI
2
is also used as a high-energy photon detector for gamma-rays and X-rays, due to its wide band gap which ensures low noise operation.[2][6][19]

Lead iodide was formerly used as a paint pigment under the name "iodine yellow. It was described by Prosper Mérimée (1830) as "not yet much known in commerce, is as bright as orpiment or chromate of lead. It is thought to be more permanent; but time only can prove its pretension to so essential a quality. It is prepared by precipitating a solution of acetate or nitrate of lead, with hydrochlorate of potassium: the nitrate produces a more brilliant yellow color."[9] However, due to the toxicity and instability of the compound it is no longer used as such.[9] It may still be used in art for bronzing and in gold-like mosaic tiles.[2]

Toxicity[edit]

Lead iodide is very toxic to human health. Ingestion will cause many acute and chronic consequences characteristic of lead poisoning.[22] [23] Lead iodide has been found to be a carcinogen in animals suggesting the same may hold true in humans.[24]

Structure[edit]

The structure of PbI
2
, as determined by X-ray powder diffraction, is primarily hexagonal close-packed system with alternating between layers of lead atoms and iodide atoms, with largely ionic bonding.[20] Weak Van der Waals interactions have been observed between lead–iodide layers.[6] The solid can also take a rhombohedral structure as well.[25][26]

Lead(II) iodide precipitates when solutions of potassium iodide and lead(II) nitrate are combined
Experiment "golden rain" where iodide of lead(II) was recrystallized from hot solution by cooling, forming crystals of golden-yellow

See also[edit]

References[edit]

  1. ^ Clever & Johnston 1980.
  2. ^ a b c d P. Patnaik (2002): Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 978-0070494398
  3. ^ Philip W. West, Jack K. Carlton (1952): The extraction of lead iodide by methyl iso-propyl ketone". Analytica Chimica Acta, volume 6, pages 406-411. doi:10.1016/S0003-2670(00)86967-6
  4. ^ "Sigma-Aldrich catalog: Lead(II) iodide 99%". www.sigmaaldrich.com. Retrieved 2016-04-29. 
  5. ^ a b c Dhiaputra et al. 2016.
  6. ^ a b c Shah et al. 1996.
  7. ^ Seth Anthony (2014): I. Cognitive and instructional factors relating to students' development of personal models of chemical systems in the general chemistry laboratory. [...]. Ph. D. Thesis, Colorado State University
  8. ^ J Jacobs and R Corrigan (1970): Lead iodide film. US Patent US3764368-A. Filed Feb 22, 1972; published Oct 9, 1973,
  9. ^ a b c Eastaugh et al. 2004.
  10. ^ Ahmad & Prakash 2012.
  11. ^ a b M. Matuchova, K. Zdansky, J. Zavadil, A. Danilewsky, F. Riesz, M.A.S. Hassan, D. Alexiew, R. Kral (2009): Study of the influence of the rare-earth elements on the properties of lead iodide. Journal of Crystal Growth, volume 311, issue 14, pages 3557–3562. doi:10.1016/j.jcrysgro.2009.04.043
  12. ^ T.K. Chaudhuri and H.N. Acharya(1982): Preparation of lead iodide films by iodination of chemically deposited lead sulphide films. Materials Research Bulletin. volume 17, issue 3, pages 279-286. doi:10.1016/0025-5408(82)90074-5
  13. ^ Declan Fleming (2015): Golden rain. Education in Chemistry video. Accessed on 2016-08-25.
  14. ^ Xinghua Zhu, Peihua Wangyang, Hui Sun, Dingyu Yang, Xiuying Gao, Haibo Tian (2016) Facile growth and characterization of freestanding single crystal PbI2 film. Materials Letters, volume 180, pages 59–62. doi:10.1016/j.matlet.2016.05.101
  15. ^ W. Conard Fernelius and Kenneth D. Detling (1934): Preparation of crystals of sparingly soluble salts. J. Chem. Educ., volume 11, issue 3, page 176. doi:10.1021/ed011p176.
  16. ^ E. Hatschek (1906) Zeit. anorg. Chem., volume 48, page 364.
  17. ^ A. R. Patel and A. Venkateswara Rao (1980): An improved design to grow larger and more perfect single crystals in gels Journal of Crystal Growth, volume 49, issue 3, pages 589-590. doi:10.1016/0022-0248(80)90134-7
  18. ^ Scaife et al. 1990.
  19. ^ a b c L. Fornaro, E. Saucedo, L. Mussio, L. Yerman, X. Ma, A. Burger (2001): Lead iodide film deposition and characterization Proc. 11th Int. Workshop on Room Temperature Semiconductor X- and Gamma-Ray Detectors and Associated Electronics; in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, volume 458, issues 1–2, pages 406–412. doi:10.1016/S0168-9002(00)00933-5
  20. ^ a b Liu et al. 2015.
  21. ^ Tonn et al. 2015.
  22. ^ Flora, Gupta & Tiwari 2012.
  23. ^ Patrick 2006.
  24. ^ "Haz-Map Category Details". hazmap.nlm.nih.gov. Retrieved 2016-04-29. 
  25. ^ Bhavsar 2011.
  26. ^ Hassan et al. 2010.


Sources[edit]

External links[edit]