Polyiodide

The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms.[1][2] The most common and simplest member is the triiodide ion, I−
3. Other known larger polyiodides include [I4]2−, [I5]−, [I6]2−, [I7]−, [I8]2−, [I9]−, [I10]2−, [I10]4−, [I11]3−, [I12]2−, [I13]3−, [I14]4-, [I16]2−, [I22]4−, [I26]3−, [I26]4−, [I28]4− and [I29]3−. All these can be considered as formed from the interaction of the I–, I2, and I−
3 building blocks.

Preparation

The polyiodides can be made by addition of stoichiometric amounts of I2 to solutions containing I− and I−
3, with the presence of large countercations to stabilize them. For example, KI3·H2O can be crystallized from a saturated solution of KI when a stoichiometric amount of I2 is added and cooled.[3]

Structure
The 14-membered ring array of iodine atoms in [([16]aneS4)PdIPd([16]aneS4)][I11
The primitive cubic lattice of iodide ions bridge by I2 molecules, present in [Cp*2Fe]4[I26

Polyiodides adopt diverse structures. Most can be considered as associations of I2, I−, and I−
3 units. Discrete polyiodides are usually linear. The more complex two- or three-dimensional network structures of chains and cages are formed as the ions interact with each other, with their shapes depending on their associated cations quite strongly, a phenomenon named dimensional caging.[4][5] The table below lists the polyiodide salts which have been structurally characterized, along with their counter-cation.[6]

Structure of higher polyiodides
AnionCounter-cationStructural description
[I2]-Na(C3H6O)+
3		linear[7][8]
[I3]−Cs+, (C4H9)4N+linear
[I4]2−[Cu(NH3)4]2+symmetric linear array of iodine atoms[9]
[I5]−[EtMe3N]+V-shaped with polymeric layers
[EtMePh2N]+V-shaped with isolated [I5]− ions
[I6]2− [NH3(CH2)8NH3]2+ almost linear [[10]]
[I7]−[Ag(18aneS6)]+an anionic network derived from a primitive rhombohedral lattice of iodide ions bridged by I2 molecules
[I8]2−[Ni(phen)3]2+regular anionic shapes, can be described as [I−
3·I2·I−
8] or [I−
3·I−
5]
[I9]−[Me2iPrPhN]+14-membered ring tied by two I2 bridges to give 10-membered rings
[Me4N]+non-octahedral, but a twisted "h"-like arrangement of I−
3 and I2 units
[I10]2−[Cd(12-crown-4)2]2+; Theophylliniumtwisted ring configuration with two I−
3 units linked by two I2 molecules[11]
[I11]3−[(16aneS4)PdIPd(16aneS4)]3+14-membered ring (9.66 × 12.64 Å) around the complex cation, with the rings interlink further to give an infinite 2D sheet
[I12]2−[Ag2(15aneS5)2]2+extended 3D spiral superstructure supported by Ag–I bonds and weak I···S interactions
[Cu(Dafone)3]2+planar configuration
[I13]3−[Me2Ph2N]+consists of zigzag chains of I− and I2
[I14]4− 4,4′-bipyridinium double hook (I−
3·I2·I−·I2·I−·I2·I−
3)[12]
[I16]2−[Me2Ph2N]+centrosymmetric arrangement of [I−
7·I2·I−
7]
[iPrMe2PhN]+the anion forms 14-membered rings catenated by I2 molecules, which further link into layers with 10- and 14-membered rings
[I22]4−[MePh3P]+two "L"-shaped [I5]− units linked by an I2 molecule and completed by two end-on [I5]− groups
[I26]3−[Me3S]+consists of [I5]− and [I7]− ions with intercalated I2 molecules
[I26]4−Cp*2Fe+an anionic network derived from a primitive cubic lattice built from I− ions, with I2 bridges on all edges and systematically removing 1⁄12 of the I2 molecules
[I29]3−Cp2Fe+an anionic 3D network with a cage-like structure of [{(I−
5)1⁄2·I2}·{(I2−
12)1⁄2·I2}·I2], with [Cp2Fe]+ ions interacting with the anion in the cavities[13]
[I∞]δ−Pyrroloperylene+•Infinite polyiodide homopolymer.[14]
Structures of some polyiodide ions.


Reactivity

Polyiodide compounds are generally sensitive to light.

Triiodide, I−
3, undergoes unimolecular photodissociation.[15][16] Polyiodide has been used to improve the scalability in the synthesis of halide perovskite photovoltaic materials.[17]

Conductivity

Solid state compounds containing linear-chain polyiodide ions exhibit enhanced conductivity[18][19] than their simple iodide counterparts. The conductivity can be drastically modified by external pressure, which changes the interatomic distances between iodine moieties and the charge distribution.[20]

See also

References
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  2. Kloo, Lars (2021), "Catenated compounds in Group 17—Polyhalides", Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, Elsevier, pp. B9780128231449000133, doi:10.1016/b978-0-12-823144-9.00013-3, ISBN 978-0-12-409547-2, S2CID 242567501, retrieved 2022-03-28
  3. Brauer, G., ed. (1963). "Potassium triiodide". Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). New York: Academic Press. p. 294.
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  6. King, R. Bruce (2005). "Chlorine, Bromine, Iodine, & Astatine: Inorganic Chemistry". Encyclopedia of Inorganic Chemistry (2nd ed.). Wiley. p. 747. ISBN 9780470862100.
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  8. Howie, R. Alan; Wardell, James L. (2003-05-15). "Polymeric tris(μ2-acetone-κ2O:O)sodium polyiodide at 120 K". Acta Crystallographica Section C Crystal Structure Communications. 59 (5): m184–m186. doi:10.1107/S0108270103006395. ISSN 0108-2701.
  9. Svensson, Per H.; Kloo, Lars (2003). "Synthesis, Structure, and Bonding in Polyiodide and Metal Iodide–Iodine Systems". Chem. Rev. 103 (5): 1649–84. doi:10.1021/cr0204101. PMID 12744691.
  10. Reiss, Guido J.; Van Megen, Martin (2013). "I62− Anion Composed of Two Asymmetric Triiodide Moieties: A Competition between Halogen and Hydrogen Bond". Inorganics. 1 (1): 3–13. doi:10.3390/inorganics1010003.
  11. Reiss, Guido J. (2019-06-26). "A cyclic I102− anion in the layered crystal structure of theophyllinium pentaiodide, C7H9I5N4O2". Zeitschrift für Kristallographie – New Crystal Structures. 234 (4): 737–739. doi:10.1515/ncrs-2019-0082. ISSN 2197-4578.
  12. Reiss, Guido J.; Megen, Martin van (2012). "Two New Polyiodides in the 4,4′-Bipyridinium Diiodide/Iodine System". Zeitschrift für Naturforschung B. 67 (1): 5–10. doi:10.1515/znb-2012-0102. ISSN 1865-7117. S2CID 5857644.
  13. Tebbe, Karl-Friedrich; Buchem, Rita (1997-06-16). "Das bisher iodreichste Polyiodid: Herstellung und Struktur von Fc3I29". Angewandte Chemie (in German). 109 (12): 1403–1405. Bibcode:1997AngCh.109.1403T. doi:10.1002/ange.19971091233.
  14. Madhu, Sheri; Evans, Hayden A.; Doan-Nguyen, Vicky V. T.; Labram, John G.; Wu, Guang; Chabinyc, Michael L.; Seshadri, Ram; Wudl, Fred (4 July 2016). "Infinite Polyiodide Chains in the Pyrroloperylene–Iodine Complex: Insights into the Starch-Iodine and Perylene-Iodine Complexes". Angewandte Chemie International Edition. 55 (28): 8032–8035. doi:10.1002/anie.201601585. PMID 27239781. S2CID 30407996.
  15. Hoops, Alexandra A.; Gascooke, Jason R.; Faulhaber, Ann Elise; Kautzman, Kathryn E.; Neumark, Daniel M. (May 2004). "Two- and three-body photodissociation of gas phase I3−". The Journal of Chemical Physics. 120 (17): 7901–7909. doi:10.1063/1.1691017. hdl:2440/34955. ISSN 0021-9606. PMID 15267705.
  16. Nakanishi, Ryuzo; Saitou, Naoya; Ohno, Tomoyo; Kowashi, Satomi; Yabushita, Satoshi; Nagata, Takashi (2007-05-28). "Photodissociation of gas-phase I3−: Comprehensive understanding of nonadiabatic dissociation dynamics". The Journal of Chemical Physics. 126 (20): 204311. doi:10.1063/1.2736691. ISSN 0021-9606. PMID 17552766.
  17. Turkevych, Ivan; Kazaoui, Said; Belich, Nikolai A.; Grishko, Aleksei Y.; Fateev, Sergey A.; Petrov, Andrey A.; Urano, Toshiyuki; Aramaki, Shinji; Kosar, Sonya; Kondo, Michio; Goodilin, Eugene A. (January 2019). "Strategic advantages of reactive polyiodide melts for scalable perovskite photovoltaics". Nature Nanotechnology. 14 (1): 57–63. doi:10.1038/s41565-018-0304-y. ISSN 1748-3395. PMID 30478274. S2CID 53784226.
  18. Alvarez, Santiago; Novoa, Juan; Mota, Fernando (1986-12-26). "The mechanism of electrical conductivity along polyhalide chains". Chemical Physics Letters. 132 (6): 531–534. doi:10.1016/0009-2614(86)87118-4.
  19. Yu, Hongtao; Yan, Lijia; He, Yaowu; Meng, Hong; Huang, Wei (2017). "An unusual photoconductive property of polyiodide and enhancement by catenating with 3-thiophenemethylamine salt". Chemical Communications. 53 (2): 432–435. doi:10.1039/C6CC08595D. ISSN 1359-7345. PMID 27965990.
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