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Micron Document

Polyiodide

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The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms.cite-ref-inorgchem-1-0[1]cite-ref-2[2] The most common 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.

Contents

• Preparation

• Structure

• Reactivity

• Conductivity

• See also

• References

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.cite-ref-3[3]

Structure

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.cite-ref-4[4]cite-ref-5[5] The table below lists the polyiodide salts which have been structurally characterized, along with their counter-cation.cite-ref-encyclo-6-0[6]

| Anion | Counter-cation | Structural description |

|---|---|---|

| [I 2 ] − | Na(C 3 H 6 O) + 3 | linear [ 7 ] [ 8 ] |

| [I 3 ] − | Cs + , (C 4 H 9 ) 4 N + | linear |

| [I 4 ] 2− | [Cu(NH 3 ) 4 ] 2+ | symmetric linear array of iodine atoms [ 9 ] |

| [I 5 ] − | [EtMe 3 N] + | V-shaped with polymeric layers |

| [I 5 ] − | [EtMePh 2 N] + | V-shaped with isolated [I 5 ] − ions |

| [I 6 ] 2− | [NH 3 (CH 2 ) 8 NH 3 ] 2+ | almost linear [ [ 10 ] ] |

| [I 7 ] − | [Ag(18aneS 6 )] + | an anionic network derived from a primitive rhombohedral lattice of iodide ions bridged by I 2 molecules |

| [I 8 ] 2− | [Ni( phen ) 3 ] 2+ | regular anionic shapes, can be described as [ I − 3 ·I 2 · I − 8 ] or [ I − 3 · I − 5 ] |

| [I 9 ] − | [Me 2 i Pr Ph N] + | 14-membered ring tied by two I 2 bridges to give 10-membered rings |

| [I 9 ] − | [Me 4 N] + | non-octahedral, but a twisted "h"-like arrangement of I − 3 and I 2 units |

| [I 10 ] 2− | [Cd( 12-crown-4 ) 2 ] 2+; Theophyllinium | twisted ring configuration with two I − 3 units linked by two I 2 molecules [ 11 ] |

| [I 11 ] 3− | [(16aneS 4 ) Pd IPd(16aneS 4 )] 3+ | 14-membered ring (9.66 × 12.64 Å ) around the complex cation, with the rings interlink further to give an infinite 2D sheet |

| [I 12 ] 2− | [Ag 2 (15aneS 5 ) 2 ] 2+ | extended 3D spiral superstructure supported by Ag–I bonds and weak I···S interactions |

| [I 12 ] 2− | [Cu(Dafone) 3 ] 2+ | planar configuration |

| [I 13 ] 3− | [Me 2 Ph 2 N] + | consists of zigzag chains of I − and I 2 |

| [I 14 ] 4− | 4,4′-bipyridinium | double hook ( I − 3 ·I 2 ·I − ·I 2 ·I − ·I 2 · I − 3 ) [ 12 ] |

| [I 16 ] 2− | [Me 2 Ph 2 N] + | centrosymmetric arrangement of [ I − 7 ·I 2 · I − 7 ] |

| [I 16 ] 2− | [ i PrMe 2 PhN] + | the anion forms 14-membered rings catenated by I 2 molecules, which further link into layers with 10- and 14-membered rings |

| [I 22 ] 4− | [MePh 3 P] + | two L-shaped [I 5 ] − units linked by an I 2 molecule and completed by two end-on [I 5 ] − groups |

| [I 26 ] 3− | [Me 3 S] + | consists of [I 5 ] − and [I 7 ] − ions with intercalated I 2 molecules |

| [I 26 ] 4− | Cp* 2 Fe + | an anionic network derived from a primitive cubic lattice built from I − ions, with I 2 bridges on all edges and systematically removing 1 ⁄ 12 of the I 2 molecules |

| [I 29 ] 3− | Cp 2 Fe + | an anionic 3D network with a cage-like structure of [{( I − 5 ) 1 ⁄ 2 ·I 2 }·{( I 2− 12 ) 1 ⁄ 2 ·I 2 }·I 2 ], with [Cp 2 Fe] + ions interacting with the anion in the cavities [ 13 ] |

| [I ∞ ] δ− | Pyrroloperylene +• | Infinite polyiodide homopolymer. [ 14 ] |

Reactivity

Polyiodide compounds are generally sensitive to light.

Triiodide, I−

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

Conductivity

Solid state compounds containing linear-chain polyiodide ions exhibit enhanced conductivitycite-ref-18[18]cite-ref-19[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.cite-ref-20[20]