Polyiodide

The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms.{{cite book|title=Inorganic Chemistry|last1=Housecroft|first1=Catherine E.|last2=Sharpe|first2=Alan G.|publisher=Pearson|year=2008|isbn=978-0-13-175553-6|edition=3rd|page=547|chapter=Chapter 17: The group 17 elements}}{{Citation |last=Kloo |first=Lars |title=Catenated compounds in Group 17—Polyhalides |date=2021 |url=https://linkinghub.elsevier.com/retrieve/pii/B9780128231449000133 |work=Reference Module in Chemistry, Molecular Sciences and Chemical Engineering |pages=1021–1049 |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-823144-9.00013-3 |isbn=978-0-12-409547-2 |s2cid=242567501 |access-date=2022-03-28}} The most common member is the triiodide ion, {{chem|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 {{chem|I|3|−}} building blocks.

Preparation

The polyiodides can be made by addition of stoichiometric amounts of I₂ to solutions containing I⁻ and {{chem|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.{{cite encyclopedia|title=Potassium triiodide|encyclopedia=Handbook of Preparative Inorganic Chemistry|edition=2nd|editor-first=G.|editor-last=Brauer|publisher=Academic Press|date=1963|location=New York|volume=1|page=294}}

Structure

File:Solid state structure of the (I11)3- ion in (((16)aneS4)PdIPd((16)aneS4))(I11).png]

File:Solid state structure of (I26)4- in (DMFc)4(I26).png]

Polyiodides adopt diverse structures. Most can be considered as associations of I₂, I⁻, and {{chem|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.{{Cite journal |last1=Svensson |first1=Per H. |last2=Gorlov |first2=Mikhail |last3=Kloo |first3=Lars |date=2008-12-15 |title=Dimensional Caging of Polyiodides |url=https://pubs.acs.org/doi/10.1021/ic801820s |journal=Inorganic Chemistry |language=en |volume=47 |issue=24 |pages=11464–11466 |doi=10.1021/ic801820s |pmid=19053351 |issn=0020-1669}}{{Cite journal |last1=García |first1=Marcos D. |last2=Martí-Rujas |first2=Javier |last3=Metrangolo |first3=Pierangelo |last4=Peinador |first4=Carlos |last5=Pilati |first5=Tullio |last6=Resnati |first6=Giuseppe |last7=Terraneo |first7=Giancarlo |last8=Ursini |first8=Maurizio |date=2011 |title=Dimensional caging of polyiodides: cation-templated synthesis using bipyridinium salts |url=http://xlink.rsc.org/?DOI=c0ce00860e |journal=CrystEngComm |language=en |volume=13 |issue=13 |pages=4411 |doi=10.1039/c0ce00860e |issn=1466-8033}} The table below lists the polyiodide salts which have been structurally characterized, along with their counter-cation.{{cite book

| title = Encyclopedia of Inorganic Chemistry | edition = 2nd

| chapter = Chlorine, Bromine, Iodine, & Astatine: Inorganic Chemistry

| first = R. Bruce | last = King

| publisher = Wiley

| year = 2005

| isbn = 9780470862100

| page = 747

}}

class="wikitable" \|+ Structure of higher polyiodides ! Anion !! Counter-cation !! Structural description
[I₂]⁻	Na(C₃H₆O){{su\|b=3\|p=+}}	linear{{cite web\|url=https://www.ch.imperial.ac.uk/rzepa/blog/?p=439\|last=Rzepa\|first=Henry\|author-link=Henry Rzepa\|title=The mystery of the Finkelstein reaction\|website=Chemistry with a twist\|date=May 16, 2009}}{{Cite journal \|last1=Howie \|first1=R. Alan \|last2=Wardell \|first2=James L. \|date=2003-05-15 \|title=Polymeric tris(μ₂-acetone-κ²O:O)sodium polyiodide at 120 K \|url=https://scripts.iucr.org/cgi-bin/paper?S0108270103006395 \|journal=Acta Crystallographica Section C Crystal Structure Communications \|volume=59 \|issue=5 \|pages=m184–m186 \|doi=10.1107/S0108270103006395 \|pmid=12743392 \|issn=0108-2701}}
[I₃]⁻	Cs⁺, (C₄H₉)₄N⁺	linear
[I₄]²⁻	[Cu(NH₃)₄]²⁺	symmetric linear array of iodine atoms{{cite journal\|first1=Per H.\|last1=Svensson\|first2=Lars\|last2=Kloo\|title=Synthesis, Structure, and Bonding in Polyiodide and Metal Iodide–Iodine Systems\|journal=Chem. Rev.\|date=2003\|volume=103\|issue=5\|pages=1649–84\|doi=10.1021/cr0204101\|pmid=12744691}}
rowspan=2 \| [I₅]⁻	[EtMe₃N]⁺	V-shaped with polymeric layers
[EtMePh₂N]⁺	V-shaped with isolated [I₅]⁻ ions
[I₆]²⁻ \|[NH₃(CH₂)₈NH₃]²⁺ \|almost linear [{{Cite journal\|last1=Reiss\|first1=Guido J.\|last2=Van Megen\|first2=Martin\|date=2013\|title=I₆²⁻ Anion Composed of Two Asymmetric Triiodide Moieties: A Competition between Halogen and Hydrogen Bond\|journal=Inorganics\|language=en\|volume=1\|issue=1\|pages=3–13\|doi=10.3390/inorganics1010003\|doi-access=free}}]
[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 [{{chem\|I\|3\|−}}·I₂·{{chem\|I\|8\|−}}] or [{{chem\|I\|3\|−}}·{{chem\|I\|5\|−}}]
rowspan=2 \| [I₉]⁻	[Me₂ⁱPr PhN]⁺	14-membered ring tied by two I₂ bridges to give 10-membered rings
[Me₄N]⁺	non-octahedral, but a twisted "h"-like arrangement of {{chem\|I\|3\|−}} and I₂ units
[I₁₀]²⁻	[Cd(12-crown-4)₂]^2+; Theophyllinium	twisted ring configuration with two {{chem\|I\|3\|−}} units linked by two I₂ molecules{{Cite journal\|last=Reiss\|first=Guido J.\|date=2019-06-26\|title=A cyclic I₁₀²⁻ anion in the layered crystal structure of theophyllinium pentaiodide, C₇H₉I₅N₄O₂\|journal=Zeitschrift für Kristallographie – New Crystal Structures\|volume=234\|issue=4\|pages=737–739\|doi=10.1515/ncrs-2019-0082\|issn=2197-4578\|doi-access=free}}
[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
rowspan=2 \| [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 ({{chem\|I\|3
}}·I₂·I⁻·I₂·I⁻·I₂·{{chem\|I\|3
}}){{Cite journal\|last1=Reiss\|first1=Guido J.\|last2=Megen\|first2=Martin van\|date=2012\|title=Two New Polyiodides in the 4,4′-Bipyridinium Diiodide/Iodine System\|journal=Zeitschrift für Naturforschung B\|volume=67\|issue=1\|pages=5–10\|doi=10.1515/znb-2012-0102\|s2cid=5857644\|issn=1865-7117\|doi-access=free}}
rowspan=2 \| [I₁₆]²⁻	[Me₂Ph₂N]⁺	centrosymmetric arrangement of [{{chem\|I\|7
}}·I₂·{{chem\|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 {{frac\|12}} of the I₂ molecules
[I₂₉]³⁻	Cp₂Fe⁺	an anionic 3D network with a cage-like structure of [{({{chem\|I\|5\|−}})_{{1/2}}·I₂}·{({{chem\|I\|12\|2−}})_{{1/2}}·I₂}·I₂], with [Cp₂Fe]⁺ ions interacting with the anion in the cavities{{Cite journal\|last1=Tebbe\|first1=Karl-Friedrich\|last2=Buchem\|first2=Rita\|date=1997-06-16\|title=Das bisher iodreichste Polyiodid: Herstellung und Struktur von Fc₃I₂₉\|journal=Angewandte Chemie\|language=de\|volume=109\|issue=12\|pages=1403–1405\|doi=10.1002/ange.19971091233\|bibcode=1997AngCh.109.1403T}}
[I_∞]^δ−	Pyrroloperylene^+•	Infinite polyiodide homopolymer.{{cite journal \|last1=Madhu \|first1=Sheri \|last2=Evans \|first2=Hayden A. \|last3=Doan-Nguyen \|first3=Vicky V. T. \|last4=Labram \|first4=John G. \|last5=Wu \|first5=Guang \|last6=Chabinyc \|first6=Michael L. \|last7=Seshadri \|first7=Ram \|last8=Wudl \|first8=Fred \|title=Infinite Polyiodide Chains in the Pyrroloperylene–Iodine Complex: Insights into the Starch-Iodine and Perylene-Iodine Complexes \|journal=Angewandte Chemie International Edition \|date=4 July 2016 \|volume=55 \|issue=28 \|pages=8032–8035 \|doi=10.1002/anie.201601585\|pmid=27239781 \|s2cid=30407996 \|doi-access= }}

File:Structures of some polyiodide ions.png

Reactivity

Polyiodide compounds are generally sensitive to light.

Triiodide, {{chem|I|3|−}}, undergoes unimolecular photodissociation.{{Cite journal |last1=Hoops |first1=Alexandra A. |last2=Gascooke |first2=Jason R. |last3=Faulhaber |first3=Ann Elise |last4=Kautzman |first4=Kathryn E. |last5=Neumark |first5=Daniel M. |date=May 2004 |title=Two- and three-body photodissociation of gas phase I3− |url=http://aip.scitation.org/doi/10.1063/1.1691017 |journal=The Journal of Chemical Physics |language=en |volume=120 |issue=17 |pages=7901–7909 |doi=10.1063/1.1691017 |pmid=15267705 |hdl=2440/34955 |issn=0021-9606|hdl-access=free }}{{Cite journal |last1=Nakanishi |first1=Ryuzo |last2=Saitou |first2=Naoya |last3=Ohno |first3=Tomoyo |last4=Kowashi |first4=Satomi |last5=Yabushita |first5=Satoshi |last6=Nagata |first6=Takashi |date=2007-05-28 |title=Photodissociation of gas-phase I3−: Comprehensive understanding of nonadiabatic dissociation dynamics |url=http://aip.scitation.org/doi/10.1063/1.2736691 |journal=The Journal of Chemical Physics |language=en |volume=126 |issue=20 |pages=204311 |doi=10.1063/1.2736691 |pmid=17552766 |issn=0021-9606}} Polyiodide has been used to improve the scalability in the synthesis of halide perovskite photovoltaic materials.{{Cite journal |last1=Turkevych |first1=Ivan |last2=Kazaoui |first2=Said |last3=Belich |first3=Nikolai A. |last4=Grishko |first4=Aleksei Y. |last5=Fateev |first5=Sergey A. |last6=Petrov |first6=Andrey A. |last7=Urano |first7=Toshiyuki |last8=Aramaki |first8=Shinji |last9=Kosar |first9=Sonya |last10=Kondo |first10=Michio |last11=Goodilin |first11=Eugene A. |date=January 2019 |title=Strategic advantages of reactive polyiodide melts for scalable perovskite photovoltaics |url=https://www.nature.com/articles/s41565-018-0304-y |journal=Nature Nanotechnology |language=en |volume=14 |issue=1 |pages=57–63 |doi=10.1038/s41565-018-0304-y |pmid=30478274 |s2cid=53784226 |issn=1748-3395}}

Conductivity

Solid state compounds containing linear-chain polyiodide ions exhibit enhanced conductivity{{Cite journal |last1=Alvarez |first1=Santiago |last2=Novoa |first2=Juan |last3=Mota |first3=Fernando |date=1986-12-26 |title=The mechanism of electrical conductivity along polyhalide chains |url=https://linkinghub.elsevier.com/retrieve/pii/0009261486871184 |journal=Chemical Physics Letters |language=en |volume=132 |issue=6 |pages=531–534 |doi=10.1016/0009-2614(86)87118-4}}{{Cite journal |last1=Yu |first1=Hongtao |last2=Yan |first2=Lijia |last3=He |first3=Yaowu |last4=Meng |first4=Hong |last5=Huang |first5=Wei |date=2017 |title=An unusual photoconductive property of polyiodide and enhancement by catenating with 3-thiophenemethylamine salt |url=http://xlink.rsc.org/?DOI=C6CC08595D |journal=Chemical Communications |language=en |volume=53 |issue=2 |pages=432–435 |doi=10.1039/C6CC08595D |pmid=27965990 |issn=1359-7345}} 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.{{Cite journal |last1=Poręba |first1=Tomasz |last2=Ernst |first2=Michelle |last3=Zimmer |first3=Dominik |last4=Macchi |first4=Piero |last5=Casati |first5=Nicola |date=2019-05-13 |title=Pressure-Induced Polymerization and Electrical Conductivity of a Polyiodide |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.201901178 |journal=Angewandte Chemie International Edition |language=en |volume=58 |issue=20 |pages=6625–6629 |doi=10.1002/anie.201901178 |pmid=30844119 |s2cid=73514885 |issn=1433-7851}}

References

Category:Anions

Category:Iodides

Category:Polyhalides