“Thallium triiodide”的意思、由来-开放百科全书

词条

Thallium triiodide

释义

Structure and preparation
References

{{chembox
| verifiedrevid = 429202780
| Name = Thallium 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
| SMILES = [Tl+].I[I-]I
| StdInChI=1S/I3.Tl/c1-3-2;/q-1;+1
| StdInChIKey=CFEVJLSKLTWQJS-UHFFFAOYSA-N
| Section2 = {{Chembox Properties
| Formula = {{math|TlI₃}}
| MolarMass = 585.097 g/mol
| Density =
| MeltingPt =
| BoilingPt = }}
| Section3 = {{Chembox Hazards
| NFPA-H = 4
| NFPA-F =
| NFPA-R =
| EUClass = {{Hazchem T+}}{{Hazchem N}}
}}
}}

Thallium triiodide is a chemical compound of thallium and iodine with formula {{math|TlI₃}}. Unlike the other thallium trihalides, which contain thallium(III), {{math|TlI₃}} is a thallium(I) compound and contains the triiodide ion, I₃⁻.

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

{{math|Tl³⁺ + 2 I⁻ → Tl⁺ + I₂}}

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

{{math|1=Tl³⁺ + 2 {{Subatomic particle|electron}} → Tl⁺; E_r° = 1.252}}

{{math|1=I₂ + 2 {{Subatomic particle|electron}} → 2 I⁻; E_r° = 0.5355}}

The favoured reaction is therefore the reduction of Tl³⁺ (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 TlI₄⁻ ion (isoelectronic with the tetraiodomercurate anion and with lead(IV) iodide).

Structure and preparation

{{math|TlI₃}} is formulated {{math|Tl⁺ I₃⁻}}, and has a similar structure to NH₄I₃, CsI₃ and RbI₃.^[1] The triiodide ion in {{math|TlI₃}} is nearly linear but is asymmetric with one iodine − iodine bond longer than the other. For comparison the dimensions of the tri-iodide, 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

{{math|TlI₃}} can be prepared by the evaporation of stoichiometric quantities of {{math|TlI}} and {{math|I₂}} in concentrated aqueous {{math|HI}}, or by reacting {{math|TlI}} with {{math|I₂}} in ethanol.

References

WebElements
{{Greenwood&Earnshaw}}

1. ^ Die Kristallstrukturen von Rubidiumtriiodid und Thalliumtriiodid Tebbe K.F., Georgy U Acta Crystallographica,C (1986) 42, 1675 {{doi|10.1107/S0108270186090972}}

3 : Thallium(I) compounds|Iodides|Metal halides

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