Thallium halides

Class of elements

The thallium halides include monohalides TlX, where thallium has oxidation state +1, trihalides TlX3, where thallium generally has oxidation state +3, and some intermediate halides containing thallium with mixed +1 and +3 oxidation states. X is a halogen. These salts find use in specialized optical settings, such as focusing elements in research spectrophotometers. Compared to the more common zinc selenide-based optics, materials such as thallium bromoiodide enable transmission at longer wavelengths. In the infrared, this allows for measurements as low as 350 cm−1 (28 μm), whereas zinc selenide is opaque by 21.5 μm, and zinc sulfide optics are generally only usable to 650 cm−1 (15 μm).

## Monohalides

[edit]

Thallium(I) iodide has the CsCl crystal structure.

The monohalides, also known as thallous halides, all contain thallium with oxidation state +1. Parallels can be drawn between the thallium(I) halides and their corresponding silver salts; for example, thallium(I) chloride and bromide are light-sensitive, and thallium(I) fluoride is more soluble in water than the chloride and bromide.

Thallium(I) fluoride
TlF is a white crystalline solid, with a melting point of 322 °C. It is readily soluble in water unlike the other Tl(I) halides. The normal room-temperature form has a similar structure to α-PbO which has a distorted rock salt structure with essentially five coordinate thallium, the sixth fluoride ion is at 370 pm. At 62 °C it transforms to a tetragonal structure. This structure is unchanged up to pressure of 40 GPa.[1]
The room temperature structure has been explained in terms of interaction between Tl 6s and the F 2p states producing strongly antibonding Tl-F states. The structure distorts to minimise these unfavourable covalent interactions.[2]

Thallium(I) chloride
TlCl is a light sensitive, white crystalline solid, melting point 430 °C. The crystal structure is the same as CsCl.
Thallium(I) bromide
TlBr is a light sensitive, pale yellow crystalline solid, melting point 460 °C. The crystal structure is the same as CsCl.

Thallium(I) iodide
At room temperature, TlI is a yellow crystalline solid, melting point 442 °C. The crystal structure is a distorted rock salt structure known as the β-TlI structure. At higher temperatures the colour changes to red with a structure the same as CsCl.[3]

## Thallium(I) mixed halides

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Thallium bromide iodide ingots

Thallium bromoiodide or thallium bromide iodide (TlBrxI1−x) and thallium bromochloride or thallium bromide chloride (TlBrxCl1−x) are mixed salts of thallium(I) that are used in spectroscopy as an optical material for transmission, refraction, and focusing of infrared radiation. The materials were first grown by R. Koops in the laboratory of Olexander Smakula at the Carl Zeiss Optical Works, Jena in 1941.[4][5] The red bromoiodide was coded KRS-5[6] and the colourless bromochloride, KRS-6[7] and this is how they are commonly known. The KRS prefix is an abbreviation of "Kristalle aus dem Schmelz-fluss", (crystals from the melt). The compositions of KRS-5 and KRS-6 approximate to TlBr0.4I0.6 and TlBr0.3Cl0.7. KRS-5 is the most commonly used, its properties of being relatively insoluble in water and non-hygroscopic, make it an alternative to KBr, CsI, and AgCl.[8]

## Trihalides

[edit]

The thallium trihalides, also known as thallic halides, are less stable than their corresponding aluminium, gallium, and indium counterparts and chemically quite distinct. The triiodide does not contain thallium with oxidation state +3 but is a thallium(I) compound and contains the linear I−3 ion.

### Thallium(III) fluoride

[edit]

TlF3 is a white solid, mp 550 °C. Its structure is the same as YF3 and β-BiF3: thallium atom is 9 coordinate (tricapped trigonal prismatic). It can be synthesised by fluoridation of the oxide, Tl2O3, with F2, BrF3, or SF4 at 300 °C.

### Thallium(III) chloride

[edit]

TlCl3 has a distorted chromium(III) chloride structure like AlCl3 and InCl3. It can be prepared] by treating TlCl with Cl2 gas.[9] Crystallization from water gives the tetrahydrate. Solid TlCl3 decomposes at 40 °C, losing chlorine to give TlCl.

### Thallium(III) bromide

[edit]

TlBr3 can be prepared] by treating TlBr with Br2 gas.[10] Crystallization from water gives the tetrahydrate. Solid TlBr3 decomposes at 40 °C, losing bromine to give TlBr.[11]

### Thallium(I) triiodide

[edit]

TlI3 is a black crystalline solid prepared from TlI and I2 in aqueous HI. It does not contain thallium(III), but has the same structure as CsI3 containing the linear I−3 ion.

## Mixed-valence halides

[edit]

As a group, these are not well characterised. They contain both Tl(I) and Tl(III), where the thallium(III) atom is present as complex anions, e.g. TlCl−4.

TlCl2
This is formulated as TlITlIIICl4.

Tl2Cl3
This yellow compound is formulated TlI3TlIIICl6.[12]

Tl2Br3
This compound is similar to Tl2Cl3 and is formulated TlI3TlIIIBr6[13]

TlBr2
This pale brown solid is formulated TlITlIIIBr4

Tl3I4
This compound has been reported as an intermediate in the synthesis of TlI3 from TlI and I2. The structure is not known.

## Halide complexes

[edit]

Thallium(I) complexes
Thallium(I) can form complexes of the type (TlX3)2− and (TlX4)3− both in solution and when thallium(I) halides are incorporated into alkali metal halides. These doped alkali metal halides have new absorption and emission nbands and are used as phosphors in scintillation radiation detectors.

Thallium(III) fluoride complexes
The salts NaTlF4 and Na3TlF6 do not contain discrete tetrahedral and octahedral anions. The structure of NaTlF4 is the same as fluorite (CaF2) with NaI and TlIII atoms occupying the 8 coordinate CaII sites. Na3TlF6 has the same structure as cryolite, Na3AlF6. In this the thallium atoms are octahedrally coordinated. Both compounds are usually considered to be mixed salts of Na+ and Tl3+.

Thallium(III) chloride complexes
Salts of tetrahedral TlCl−4 and octahedral TlCl3−6 are known with various cations.

Salts containing TlCl2−5 with a square pyramidal structure are known. Some salts that nominally contain TlCl2−5 actually contain the dimeric anion Tl2Cl4−10, long chain anions where TlIII is 6 coordinate and the octahedral units are linked by bridging chlorine atoms, or mixed salts of TlIIICl4 and TlIIICl6.[14]

The ion Tl2Cl3−9, where thallium atoms are octahedrally coordinated with three bridging chlorine atoms, has been identified in the caesium salt, Cs3Tl2Cl9.

Thallium(III) bromide complexes
Salts of TlIIIBr−4 and TlIIIBr3−6 are known with various cations.

The TlBr2−5 anion has been characterised in a number of salts and is trigonal bipyramidal. Some other salts that nominally contain TlBr2−5 are mixed salts containing TlBr−4 and Br−.[15]

Thallium(III) iodide complexes
Salts of TlIIII−4 are known. The TlIII anion is stable even though the triiodide is a thallium(I) compound.

## References

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1. ^ Häussermann, Ulrich; Berastegui, Pedro; Carlson, Stefan; Haines, Julien; Léger, Jean-Michel (2001-12-17). "TlF and PbO under High Pressure: Unexpected Persistence of the Stereochemically Active Electron Pair". Angewandte Chemie (in German). 113 (24). Wiley: 4760–4765\. Bibcode:2001AngCh.113.4760H. doi:10.1002/1521-3757(20011217)113:24<4760::aid-ange4760>3.0.co;2-6. ISSN 0044-8249.
2. ^ Mudring, Anja Verena (2007). "Thallium Halides – New Aspects of the Stereochemical Activity of Electron Lone Pairs of Heavier Main Group Elements". European Journal of Inorganic Chemistry. 2007 (6). Wiley: 882–890\. doi:10.1002/ejic.200600975. ISSN 1434-1948.
3. ^ Mir, Wasim J.; Warankar, Avinash; Acharya, Ashutosh; Das, Shyamashis; Mandal, Pankaj; Nag, Angshuman (2017). "Colloidal thallium halide nanocrystals with reasonable luminescence, carrier mobility and diffusion length". Chemical Science. 8 (6): 4602–4611\. doi:10.1039/C7SC01219E. PMC 5618336. PMID 28970882.
4. ^ Koops, R. (1948). "Optical structural subjects from binary mixed crystals". Optik (3): 298–304.
5. ^ Smakula, A.; Kalnajs, J.; Sils, V. (March 1953). "Inhomogeneity of Thallium Halide Mixed Crystals and Its Elimination". Laboratory for Insulation Research Technical Report 67. Massachusetts Institute of Technology. Retrieved October 17, 2012.
6. ^ Crystran Data for KRS5 https://www.crystran.co.uk/optical-materials/krs5-thallium-bromo-iodide-tlbr-tli
7. ^ Crystran Data for KRS6 https://www.crystran.co.uk/optical-materials/krs6-thallium-bromo-chloride-tlbr-tlcl
8. ^ Frank Twyman (1988) Prism and Lens Making: A Textbook for Optical Glassworkers CRC Press ISBN 0-85274-150-2, page 170
9. ^ E. Dönges (1963). "Thallium(IIl) ChlorideiI". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2\. NY, NY: Academic Press. p. 890.
10. ^ E. Dönges (1963). "Thallium(IIl) ChlorideiI". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2\. NY, NY: Academic Press. p. 890.
11. ^ Glaser, Julius; Fjellvåg, Helmer; Kjekshus, Arne; Andresen, Arne F.; Sokolov, V. B.; Spiridonov, V. P.; Strand, T. G. (1979). "Crystal and Molecular Structure of Thallium(III) Bromide Tetrahydrate and Thallium(III) Chloride Tetrahydrate, a Redetermination". Acta Chemica Scandinavica. 33A. Danish Chemical Society: 789–794\. doi:10.3891/acta.chem.scand.33a-0789. ISSN 0904-213X.
12. ^ Böhme, Reinhild; Rath, Jörg; Grunwald, Bernd; Thiele, Gerhard (1980-11-01). "Über zwei Modifikationen von "Tl2Cl3"-valenzgemischten Thallium(I)-hexahalogenothallaten(III) Tl3 [TlCl6] / On Two Modifications of "Tl2Cl3"-Mixed Valence Thallium(I)-hexahalogenothallates(III)". Zeitschrift für Naturforschung B. 35 (11). Walter de Gruyter GmbH: 1366–1372\. doi:10.1515/znb-1980-1108. ISSN 1865-7117.
13. ^ Ackermann, Rupprecht; Hirschle, Christian; Rotter, Heinz W.; Thiele, Gerhard (2002). "Mixed-Valence Thallium(I, III) Bromides The Crystal Structure of α—Tl2Br3". Zeitschrift für anorganische und allgemeine Chemie (in German). 628 (12). Wiley: 2675–2682\. doi:10.1002/1521-3749(200212)628:12<2675::aid-zaac2675>3.0.co;2-4. ISSN 0044-2313.
14. ^ James, Margaret Ann; Clyburne, Jason A.C.; Linden, Anthony; James, Bruce D.; Liesegang, John; Zuzich, Vilma (1996-08-01). "Structural diversity in thallium chemistry: structures of four chlorothallate(III) salts including a novel compound containing three geometrically different anions". Canadian Journal of Chemistry. 74 (8). Canadian Science Publishing: 1490–1502\. doi:10.1139/v96-166. ISSN 0008-4042.
15. ^ Linden, Anthony; Nugent, Kerry W.; Petridis, Alexander; James, Bruce D. (1999). "Structural diversity in thallium chemistry". Inorganica Chimica Acta. 285 (1). Elsevier BV: 122–128\. doi:10.1016/s0020-1693(98)00339-9. ISSN 0020-1693.

## Further information

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1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
2. Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5

* v
* t
* e

Thallium compounds

Neg. ox. states|

* Thallides

Thallium(I)|

* TlN3
* TlOH
* TlI
* TlBr
* Tl2CO3
* TlCl
* TlF
* TlPF6
* TlNO3
* Tl2O
* Tl2SO4
* Tl2S
* Tl2Te
* TlI3
* TBCCO

| Organothallium(I)|

* TlC2H3O2
* Tl2C3H2O4
* TlC5H5

|

Thallium(III)|

* TlH3
* Tl(OH)3
* Tl2O3
* Tl(NO3)3
* Tl(CH3COO)3
* TlF3
* Tl(CF3COO)3

* v
* t
* e

Fluorine compounds

* v
* t
* e

Salts and covalent derivatives of the fluoride ion

| HF |  |  |  | ?HeF2

|
|
|
|

LiF | BeF2 | BF
BF3
B2F4
+BO3 | CF4
CxFy
+CO3 | NF3
FN3
N2F2

N2F4
NF2
?NF5

+NO3 | OF2
O2F2

O3F2
O4F2
?OF4 | F2 | Ne
NaF | MgF2 | AlF
AlF3 | SiF4 | P2F4
PF3
PF5
+PO4 | S2F2
SF2
S2F4
SF3
SF4
S2F10
SF6
+SO4 | ClF
ClF3
ClF5 | ?ArF2
?ArF4
KF | CaF
CaF2 |  | ScF3 | TiF2
TiF3
TiF4 | VF2
VF3
VF4
VF5 | CrF2
CrF3
CrF4
CrF5
?CrF6 | MnF2
MnF3
MnF4
?MnF5 | FeF2
FeF3
FeF4 | CoF2
CoF3
CoF4 | NiF2
NiF3
NiF4 | CuF
CuF2
?CuF3 | ZnF2 | GaF2
GaF3 | GeF2
GeF4 | AsF3
AsF5 | Se2F2
SeF4
SeF6
+SeO3 | BrF
BrF3
BrF5 | KrF2
?KrF4
?KrF6
RbF | SrF
SrF2 |  | YF3 | ZrF2
ZrF3
ZrF4 | NbF4
NbF5 | MoF4
MoF5
MoF6 | TcF4
TcF

TcF6 | RuF3
RuF

RuF5
RuF6 | RhF3
RhF4
RhF5
RhF6 | PdF2
Pd[PdF6]
PdF4
?PdF6 | Ag2F
AgF
AgF2
AgF3 | CdF2 | InF
InF3 | SnF2
SnF4 | SbF3
SbF5 | TeF4
?Te2F10
TeF6
+TeO3 | IF
IF3
IF5
IF7
+IO3 | XeF2
XeF4
XeF6
?XeF8
CsF | BaF2 |  | LuF3 | HfF4 | TaF5 | WF4
WF5
WF6 | ReF4
ReF5
ReF6
ReF7 | OsF4
OsF5
OsF6
?OsF

?OsF
8 | IrF2
IrF3
IrF4
IrF5
IrF6 | PtF2
Pt[PtF6]
PtF4
PtF5
PtF6 | AuF
AuF3
Au2F10
?AuF6
AuF5•F2 | Hg2F2
HgF2
?HgF4 | TlF
TlF3 | PbF2
PbF4 | BiF3
BiF5 | PoF2
PoF4
PoF6 | AtF
?AtF3
?AtF5 | RnF2
?RnF

?RnF

FrF  | RaF2 |  | LrF3 | Rf  | Db  | Sg  | Bh  | Hs  | Mt  | Ds  | Rg  | Cn  | Nh  | Fl  | Mc  | Lv  | Ts  | Og
| ↓  |  |
| LaF3 | CeF3
CeF4 | PrF3
PrF4 | NdF2
NdF3
NdF4 | PmF3 | SmF
SmF2
SmF3 | EuF2
EuF3 | GdF3 | TbF3
TbF4 | DyF2
DyF3
DyF4 | HoF3 | ErF3 | TmF2
TmF3 | YbF2
YbF3
AcF3 | ThF2
ThF3
ThF4 | PaF4
PaF5 | UF3
UF4
UF5
UF6 | NpF3
NpF4
NpF5
NpF6 | PuF3
PuF4
PuF5
PuF6 | AmF2
AmF3
AmF4
?AmF6 | CmF3
CmF4
?CmF6 | BkF3
BkF
4 | CfF3
CfF4 | EsF3
EsF4
?EsF6 | Fm  | MdF3 | No

PF−6, AsF−6, SbF−6 compounds|

* AgPF6
* KAsF6
* LiAsF6
* NaAsF6
* HPF6
* HSbF6
* NH4PF6
* LiSbF6
* KPF6
* KSbF6
* LiPF6
* NaPF6
* NaSbF6
* TlPF6

AlF2−5, AlF3−6 compounds|

* (NH4)3[AlF6]
* Cs2AlF5
* Li3AlF6
* K3AlF6
* Na3AlF6

chlorides, bromides, iodides
and pseudohalogenides|

* BaClF
* SiIBrClF
* BrSO3F
* Br(SO3F)3
* CFN
* ClFO2
* PbFBr
* PbFCl
* SrFCl

SiF2−6, GeF2−6 compounds|

* BaSiF6
* BaGeF6
* (NH4)2SiF6
* Na2[SiF6]
* K2[SiF6]
* Li2GeF6
* Li2SiF6

Oxyfluorides|

* AcOF
* BrOF3
* BrO2F
* ErOF
* HoOF
* BrO3F
* NdOF
* LaOF
* SmOF
* TbOF
* ThOF2
* VOF

* TcO

* PrOF
* PuOF
* WOF

* YOF
* ClOF3
* ClO2F3

Organofluorides|

* CBrF3
* CBr2F2
* CBr3F
* CClF3
* CCl2F2
* CCl3F
* CF2O
* CF3I
* CHF3
* CH2F2
* CH3F
* C2Cl3F3
* C2H3F
* C6H5F
* C7H5F3
* C15F33N
* C3H5F
* C6H11F

with transition metal,
lanthanide, actinide, ammonium|

* VOF3
* CrOF4
* CrF2O2
* NH4F
* (NH4)3CrF6
* (NH4)3GaF6
* (NH4)2GeF6
* (NH4)3FeF6
* (NH4)3InF6
* NH4NbF6
* (NH4)2SnF6
* NH4TaF6
* (NH4)3VF6
* (NH4)2ZrF6
* CsXeF7
* Li2SnF6
* Li2TiF6
* LiWF6
* Li2ZrF6
* K2TiF6
* Rb2TiF6
* Na2TiF6
* Na2ZrF6
* K2NbF7
* K2TaF7
* K2ZrF6
* UO2F2

nitric acids|

* FNO
* FNO2
* FNO3

bifluorides|

* KHF2
* NaHF2
* NH4HF2

thionyl, phosphoryl,
and iodosyl|

* FN3O2S
* F2OS
* F3OP
* PSF3
* IOF3
* IO3F
* F2O6S2
* ISO3F
* IOF5
* IO2F
* IO2F3

Chemical formulas
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