Tellurium tetraiodide

Tellurium tetraiodide (TeI₄) is an inorganic chemical compound. It has a tetrameric structure which is different from the tetrameric solid forms of TeCl₄ and TeBr₄.^[2] In TeI₄ the Te atoms are octahedrally coordinated and edges of the octahedra are shared.^[2]

Tellurium tetraiodide

Names
Other names tellurium(IV) iodide
Identifiers
CAS Number	7790-48-9 Y
3D model (JSmol)	Interactive image
ChemSpider	74232
ECHA InfoCard	100.029.282
EC Number	232-210-5
PubChem CID	82255
UNII	ZB48I033V5 Y
CompTox Dashboard (EPA)	DTXSID1064877
InChI InChI=1S/I4Te/c1-5(2,3)4 Key: XCOKHDCPVWVFKS-UHFFFAOYSA-N
SMILES [Te](I)(I)(I)I
Properties
Chemical formula	TeI4
Molar mass	635.218 g/mol
Appearance	black crystals
Density	5.05 g/cm3, solid
Melting point	280 °C (536 °F; 553 K)
Structure
Crystal structure	orthorhombic
Hazards
GHS labelling:[1]
Pictograms
Signal word	Danger
Hazard statements	H302, H312, H314, H332
Precautionary statements	P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P322, P330, P363, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation

Tellurium tetraiodide can be prepared by reacting Te and iodomethane, CH₃I.^[2] In the vapour TeI₄ dissociates:^[3]

TeI₄ → TeI₂ + I₂

It can be also obtained by reacting telluric acid with hydrogen iodide.^[4]

Te(OH)₆ + HI → TeI₄ + I₂ + 6 H₂O

It can also be obtained by reacting the elements, which can also produce tellurium diiodide and tellurium monoiodide, depending on the reaction conditions:^[5]

Te + 2 I₂ → TeI₄

TeI₄ → TeI₂ + I₂

Properties

Tellurium tetraiodide is an iron-gray solid that decomposes slowly in cold water and quickly in warm water to form tellurium dioxide and hydrogen iodide.^[6] It is stable even in moist air and decomposes when heated, releasing iodine. It is soluble in hydriodic acid to form H[TeI₅] and it is slightly soluble in acetone.^[4]

Tellurium tetraiodide is a conductor when molten, dissociating into the ions TeI₃⁺ and I⁻. In solvents with donor properties such as acetonitrile, CH₃CN ionic complexes are formed which make the solution conducting:^[3]

TeI₄ + 2 CH₃CN → (CH₃CN)₂TeI₃⁺ + I⁻

Five modifications of tellurium tetraiodide are known, all of which are composed of tetrameric molecules.^[7] The δ form is the most thermodynamically stable form. This is structurally derived (as well as the α, β and γ forms) from the ε form.