polyiodide

The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms. The most common member is the triiodide ion, . Other known larger polyiodides include [I 4 ] 2− , [I 5 ] − , [I 6 ] 2− , [I 7 ] − , [I 8 ] 2− , [I 9 ] − , [I 10 ] 2− , [I 10 ] 4− , [I 11 ] 3− , [I 12 ] 2− , [I 13 ] 3− , [I 14 ] 4- , [I 16 ] 2− , [I 22 ] 4− , [I 26 ] 3− , [I 26 ] 4− , [I 28 ] 4− and [I 29 ] 3− . All these can be considered as formed from the interaction of the I – , I 2 , and building blocks.

The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms. The most common member is the triiodide ion, . Other known larger polyiodides include [I 4 ] 2− , [I 5 ] − , [I 6 ] 2− , [I 7 ] − , [I 8 ] 2− , [I 9 ] − , [I 10 ] 2− , [I 10 ] 4− , [I 11 ] 3− , [I 12 ] 2− , [I 13 ] 3− , [I 14 ] 4- , [I 16 ] 2− , [I 22 ] 4− , [I 26 ] 3− , [I 26 ] 4− , [I 28 ] 4− and [I 29 ] 3− . All these can be considered as formed from the interaction of the I – , I 2 , and building blocks. ==Preparation== The polyiodides can be made by addition of stoichiometric amounts of I 2 to solutions containing I − and , with the presence of large countercations to stabilize them. For example, KI 3 ·H 2 O can be crystallized from a saturated solution of KI when a stoichiometric amount of I 2 is added and cooled. ==Structure== [[File:Solid state structure of the (I11)3- ion in (((16)aneS4)PdIPd((16)aneS4))(I11).png|right|thumb|300px|The 14-membered ring array of iodine atoms in [([16]aneS 4 )PdIPd([16]aneS 4 )][I 11 ] [[File:Solid state structure of (I26)4- in (DMFc)4(I26).png|right|thumb|300px|The primitive cubic lattice of iodide ions bridge by I 2 molecules, present in [Cp* 2 Fe] 4 [I 26 ] Polyiodides adopt diverse structures. Most can be considered as associations of I 2 , I − , and 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. The table below lists the polyiodide salts which have been structurally characterized, along with their counter-cation. ==Reactivity== Polyiodide compounds are generally sensitive to light. Triiodide, , undergoes unimolecular photodissociation. Polyiodide has been used to improve the scalability in the synthesis of halide perovskite photovoltaic materials. ==Conductivity== Solid state compounds containing linear-chain polyiodide ions exhibit enhanced conductivity 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. ==See also== Triiodide Polyhalogen ions Iodine–starch test Dye-sensitized solar cell Halogen bond Catenation Inorganic polymer ==References==

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