thallium triiodide

{{chembox

| verifiedrevid = 429202780

| Name = Thallium(I) triiodide

| ImageFile = Thallium-triiodide-xtal-3D-SF.png

| ImageName = Thallium triiodide

| IUPACName = Thallium(I) triiodide

| OtherNames = thallous triiodide

| Section1 = {{Chembox Identifiers

| CASNo_Ref = {{cascite|correct|??}}

| CASNo = 60488-29-1

| CASNo1 = 13453-37-7

| EC_number = 236-627-3

| PubChem = 20233350

| ChemSpiderID = 14888331

| DTXSID = DTXSID70928661

| SMILES = [Tl+].I[I-]I

| StdInChI=1S/I3.Tl/c1-3-2;/q-1;+1

| StdInChIKey=CFEVJLSKLTWQJS-UHFFFAOYSA-N

}}

| Section2 = {{Chembox Properties

| Formula = {{chem2|TlI3}}

| Tl=1|I=3

| Density =

| MeltingPt =

| BoilingPt =

| Appearance = black crystalline solid

}}

| Section3 = {{Chembox Hazards

| NFPA-H = 4

| NFPA-F =

| NFPA-R =

| GHSPictograms = {{GHS06}}{{GHS08}}{{GHS09}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|300|330|373|411}}

| PPhrases = {{P-phrases|}}

}}

| Section9 = {{Chembox Related

| OtherAnions =

| OtherCations = {{ubl|Ammonium triiodide|Rubidium triiodide|Caesium triiodide}}

| OtherCompounds = Phosphorus heptabromide ({{chem2|[PBr4]+[Br3]-}})

}}

}}

Thallium triiodide, more precisely thallium(I) triiodide is a chemical compound of thallium and iodine with empirical formula {{chem2|TlI3}}. Unlike the other thallium trihalides, which contain thallium(III), {{chem2|TlI3}} is actually a thallium(I) salt containing thallium(I) cations {{chem2|Tl+}} and triiodide anions {{chem2|[I3]-}}, and thus has the chemical formula {{chem2|Tl+[I3]-}}. It is a black crystalline solid.

An appreciation as to why {{chem2|Tl+}} is not oxidised to {{chem2|Tl(3+)}} in the reaction:

:{{chem2|Tl(3+) + 2 I− → Tl+ + I2}}

can be gained by considering the standard reduction potentials of the half-cells which are:

:{{chem2|Tl(3+) + 2 e- → Tl+}};{{pad|2.5em}}E_r° = 1.252

:{{chem2|I2 + 2 e- → 2 I−}};{{pad|2.5em}}E_r° = 0.5355

The favoured reaction is therefore the reduction of {{chem2|Tl(3+)}} to {{chem2|Tl+}} (1.252 > 0.5355).

Using standard electrode potentials in this way must be done with caution as factors such as complex formation and solvation may affect the reaction. {{chem2|TlI3}} is no exception as it is possible to stabilise thallium(III) with excess {{chem2|I-}} forming the tetraiodothallate(III) ion {{chem2|[TlI4]-}} (isoelectronic with the tetraiodomercurate anion {{chem2|[HgI4](2-)}} and with lead(IV) iodide {{chem2|PbI4}}).