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Zinc iodide
Chemical compound

Zinc iodide is the inorganic compound with the formula ZnI2. It exists both in anhydrous form and as a dihydrate. Both are white and readily absorb water from the atmosphere. It has no major application.

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Preparation

It can be prepared by the direct reaction of zinc and iodine in water12 or refluxing ether:3

Zn + I2 → ZnI2

Absent a solvent, the elements do not combine directly at room temperature.4

Structure as solid, gas, and in solution

The structure of solid ZnI2 is unusual relative to the dichloride. While zinc centers are tetrahedrally coordinated, as in ZnCl2, groups of four of these tetrahedra share three vertices to form “super-tetrahedra” of composition {Zn4I10}, which are linked by their vertices to form a three-dimensional structure.5 These "super-tetrahedra" are similar to the P4O10 structure.67

Molecular ZnI2 is linear as predicted by VSEPR theory with a Zn-I bond length of 238 pm.8

In aqueous solution the following have been detected: Zn(H2O)62+, [ZnI(H2O)5]+, tetrahedral ZnI2(H2O)2, ZnI3(H2O)−, and ZnI42−.9

Applications

  • Zinc iodide is often used as an x-ray opaque penetrant in industrial radiography to improve the contrast between the damage and intact composite.1011
  • United States patent 4,109,065 12 describes a rechargeable aqueous zinc-halogen cell that includes an aqueous electrolytic solution containing a zinc salt selected from the class consisting of zinc bromide, zinc iodide, and mixtures thereof, in both positive and negative electrode compartments.
  • In combination with osmium tetroxide, ZnI2 is used as a stain in electron microscopy.13
  • As a Lewis acid, zinc iodide catalyzes for the conversion of methanol to triptane and hexamethylbenzene.14
  • It can be used as a topical antiseptic.15

References

  1. F. Wagenknecht; R. Juza (1963). "Zinc iodide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY, NY: Academic Press. p. 1073. ↩

  2. DeMeo, S. (1995). "Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory". Journal of Chemical Education. 72 (9): 836. Bibcode:1995JChEd..72..836D. doi:10.1021/ed072p836. https://pubs.acs.org/doi/abs/10.1021/ed072p836 ↩

  3. Eagleson, M. (1994). Concise Encyclopedia Chemistry. Walter de Gruyter. ISBN 3-11-011451-8. 3-11-011451-8 ↩

  4. Gilbert, George; Houston, Kelly; Jacobsen, Jerrold J.; Phillips, David (2022) [6 Mar 2012]. Zinc iodine reaction (web video). American Chemical Society, Division of Chemical Education – via ChemEdX. https://www.chemedx.org/video/zinc-iodine-reaction ↩

  5. Wells, A. F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford Science Publications. ISBN 0-19-855370-6. 0-19-855370-6 ↩

  6. Wells, A. F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford Science Publications. ISBN 0-19-855370-6. 0-19-855370-6 ↩

  7. Fourcroy, P. H.; Carré, D.; Rivet, J. (1978). "Structure Cristalline de l'Iodure de Zinc ZnI2". Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry. 34 (11): 3160–3162. Bibcode:1978AcCrB..34.3160F. doi:10.1107/S0567740878010390. /wiki/Bibcode_(identifier) ↩

  8. Wells, A. F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford Science Publications. ISBN 0-19-855370-6. 0-19-855370-6 ↩

  9. Wakita, H.; Johansson, G.; Sandström, M.; Goggin, P. L.; Ohtaki, H. (1991). "Structure determination of zinc iodide complexes formed in aqueous solution". Journal of Solution Chemistry. 20 (7): 643–668. doi:10.1007/BF00650714. S2CID 97496242. /wiki/Doi_(identifier) ↩

  10. Baker, A.; Dutton, S.; Kelly, D., eds. (2004). Composite Materials for Aircraft Structures (2nd ed.). AIAA (American Institute of Aeronautics & Astronautics). ISBN 1-56347-540-5. 1-56347-540-5 ↩

  11. Ezrin, M. (1996). Plastics Failure Guide. Hanser Gardner Publications. ISBN 1-56990-184-8. 1-56990-184-8 ↩

  12. US patent 4109065, Will, F. G.; Secor, F. W., "Rechargeable aqueous zinc-halogen cell", issued 1978-08-22, assigned to General Electric https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=US4109065 ↩

  13. Hayat, M. A. (2000). Principles and Techniques of Electron Microscopy: Biological Applications (4th ed.). Cambridge University Press. ISBN 0-521-63287-0. 0-521-63287-0 ↩

  14. Bercaw, John E.; Diaconescu, Paula L.; Grubbs, Robert H.; Kay, Richard D.; Kitching, Sarah; Labinger, Jay A.; Li, Xingwei; Mehrkhodavandi, Parisa; Morris, George E. (2006-11-01). "On the Mechanism of the Conversion of Methanol to 2,2,3-Trimethylbutane (Triptane) over Zinc Iodide". The Journal of Organic Chemistry. 71 (23): 8907–8917. doi:10.1021/jo0617823. ISSN 0022-3263. PMID 17081022. /wiki/Paula_Diaconescu ↩

  15. Rohe, Dieter M. M.; Wolf, Hans Uwe (2007), "Zinc Compounds", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, pp. 1–6, doi:10.1002/14356007.a28_537, ISBN 978-3527306732 978-3527306732 ↩