Thallium_triiodide Knowpia

Thallium triiodide
Names
	IUPAC name thallium(I) (triiodide)
	Other names thallous triiodide
Identifiers
CAS Number	60488-29-1 ; 13453-37-7;
3D model (JSmol)	Interactive image;
ChemSpider	14888331;
EC Number	236-627-3;
PubChem CID	20233350;
CompTox Dashboard (EPA)	DTXSID70928661;
	InChI InChI=1S/I3.Tl/c1-3-2;/q-1;+1 Key: CFEVJLSKLTWQJS-UHFFFAOYSA-N;
	SMILES [Tl+].I[I-]I;
Properties
Chemical formula	I3Tl
Molar mass	585.09 g·mol−1
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H300, H330, H373, H411
NFPA 704 (fire diamond)	4
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Thallium triiodide is a chemical compound of thallium and iodine with formula $TlI 3$ . Unlike the other thallium trihalides, which contain thallium(III), $TlI 3$ is a thallium(I) salt and contains the triiodide ion, I⁻
₃.

An appreciation as to why Tl⁺ is not oxidised to Tl³⁺ in the reaction:

Tl³⁺ + 2 I⁻ → Tl⁺ + I₂

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

Tl³⁺ + 2
e⁻
→ Tl⁺; E_r° = 1.252

I₂ + 2
e⁻
→ 2 I⁻; E_r° = 0.5355

The favoured reaction is therefore the reduction of Tl³⁺ to 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. TlI₃ is no exception as it is possible to stabilise thallium(III) with excess I⁻ forming the tetraiodothallate (TlI⁻
₄) ion (isoelectronic with the tetraiodomercurate anion and with lead(IV) iodide).

Structure and preparation edit

TlI₃ is formulated Tl⁺
I⁻
₃, and has a similar structure to NH₄I₃, CsI₃ and RbI₃.^[1] The triiodide ion in TlI₃ is nearly linear but is asymmetric with one iodine–iodine bond longer than the other. For comparison the dimensions of the triiodide, I_a–I_b–I_c, ions in the different compounds are shown below:

compound	I_a–I_b (pm)	I_b–I_c (pm)	angle (°)
TlI₃	306.3	282.6	177.90
RbI₃	305.1	283.3	178.11
CsI₃	303.8	284.2	178.00
NH₄I₃	311.4	279.7	178.55

TlI₃ can be prepared by the evaporation of stoichiometric quantities of thallium(I) iodide ( $TlI$ ) and iodine in concentrated aqueous hydriodic acid, or by reacting TlI with iodine in ethanol.

References edit

WebElements
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

^ Tebbe, K.F.; Georgy, U. (1985-12-15). "Die Kristallstrukturen von Rubidiumtriiodid und Thalliumtriiodid". Acta Crystallographica C (in German). 42 (12): 1675–1678. doi:10.1107/S0108270186090972.

[1] Tebbe, K.F.; Georgy, U. (1985-12-15). "Die Kristallstrukturen von Rubidiumtriiodid und Thalliumtriiodid". Acta Crystallographica C (in German). 42 (12): 1675–1678. doi:10.1107/S0108270186090972.

[1]

Summary

Structure and preparation edit

References edit