Thallium halides#Trihalides

File:Thallium-iodide-3D-vdW.png

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.{{cite journal |last1=Häussermann |first1=Ulrich |last2=Berastegui |first2=Pedro |last3=Carlson |first3=Stefan |last4=Haines |first4=Julien |last5=Léger |first5=Jean-Michel |title=TlF and PbO under High Pressure: Unexpected Persistence of the Stereochemically Active Electron Pair |journal=Angewandte Chemie |publisher=Wiley |volume=113 |issue=24 |date=2001-12-17 |issn=0044-8249 |doi=10.1002/1521-3757(20011217)113:24<4760::aid-ange4760>3.0.co;2-6 |pages=4760–4765 |bibcode=2001AngCh.113.4760H |language=de}}

: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.{{cite journal |last=Mudring |first=Anja Verena |title=Thallium Halides – New Aspects of the Stereochemical Activity of Electron Lone Pairs of Heavier Main Group Elements |journal=European Journal of Inorganic Chemistry |publisher=Wiley |volume=2007 |issue=6 |year=2007 |issn=1434-1948 |doi=10.1002/ejic.200600975 |pages=882–890}}

;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.{{cite journal |last1=Mir |first1=Wasim J. |last2=Warankar |first2=Avinash |last3=Acharya |first3=Ashutosh |last4=Das |first4=Shyamashis |last5=Mandal |first5=Pankaj |last6=Nag |first6=Angshuman |title=Colloidal thallium halide nanocrystals with reasonable luminescence, carrier mobility and diffusion length |journal=Chemical Science |volume=8 |issue=6 |pages=4602–4611 |language=en |doi=10.1039/C7SC01219E |pmid=28970882 |pmc=5618336 |date=2017}}

File:6 KRS5 Tallium Bromide Iodide ingots Crystaltechno.jpg

Thallium bromoiodide or thallium bromide iodide ({{chem2|TlBr_{x}I_{1−x}|}}) and thallium bromochloride or thallium bromide chloride ({{chem2|TlBr_{x}Cl_{1−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.{{cite journal |title=Optical structural subjects from binary mixed crystals |author=Koops, R. |journal=Optik |year=1948 |issue=3 |pages=298–304}}{{cite web |url=https://docs.google.com/viewer?a=v&q=cache:NsfLFcXY8OQJ:www.dtic.mil/cgi-bin/GetTRDoc%3FAD%3DAD0008948+&hl=en&gl=nz&pid=bl&srcid=ADGEESiGn5WoJc2xFvblN62oU19Sb_DPH8xnbL40R2liaoPVYG5QUEHebV_2rSjFEchjQC41LbtYT6eKeX1xrM23nRim4vcLiVFhc7y5IW52zmgixui72dOtSH-ppKEwBlCME2T-xz-P&sig=AHIEtbSwEWXnARSOjawhenrSc3QLPk4JlA |title=Inhomogeneity of Thallium Halide Mixed Crystals and Its Elimination |publisher=Massachusetts Institute of Technology |work=Laboratory for Insulation Research Technical Report 67 |date=March 1953 |access-date=October 17, 2012 |last1=Smakula |first1=A. |author-link1=Olexander Smakula |last2=Kalnajs |first2=J. |last3=Sils |first3=V.}} The red bromoiodide was coded KRS-5Crystran Data for KRS5 https://www.crystran.co.uk/optical-materials/krs5-thallium-bromo-iodide-tlbr-tli and the colourless bromochloride, KRS-6Crystran Data for KRS6 https://www.crystran.co.uk/optical-materials/krs6-thallium-bromo-chloride-tlbr-tlcl 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 {{chem2|TlBr0.4I0.6}} and {{chem2|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.Frank Twyman (1988) Prism and Lens Making: A Textbook for Optical Glassworkers CRC Press {{ISBN|0-85274-150-2}}, page 170

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 {{chem2|I3-|link=triiodide}} ion.

:TlF₃ is a white solid, mp 550 °C. Its structure is the same as {{chem2|YF3|link=yttrium(III) fluoride}} and β-{{chem2|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.

:{{chem2|TlCl3}} has a distorted chromium(III) chloride structure like {{chem2|AlCl3|link=aluminium chloride}} and {{chem2|InCl3}}. It can be prepared] by treating {{chem2|TlCl|link=thallium(I) chloride}} with {{chem2|Cl2}} gas.{{cite book|author=E. Dönges|chapter=Thallium(IIl) ChlorideiI|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2|pages=890}} Crystallization from water gives the tetrahydrate. Solid {{chem2|TlCl3}} decomposes at 40 °C, losing chlorine to give {{chem2|TlCl|link=thallium(I) chloride}}.

::{{chem2|TlBr3}} can be prepared] by treating {{chem2|TlBr|link=thallium(I) chloride}} with {{chem2|Br2}} gas.{{cite book|author=E. Dönges|chapter=Thallium(IIl) ChlorideiI|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2|pages=890}} Crystallization from water gives the tetrahydrate. Solid {{chem2|TlBr3}} decomposes at 40 °C, losing bromine to give {{chem2|TlBr|link=thallium(I) bromide}}.{{cite journal |last1=Glaser |first1=Julius |last2=Fjellvåg |first2=Helmer |last3=Kjekshus |first3=Arne |last4=Andresen |first4=Arne F. |last5=Sokolov |first5=V. B. |last6=Spiridonov |first6=V. P. |last7=Strand |first7=T. G. |title=Crystal and Molecular Structure of Thallium(III) Bromide Tetrahydrate and Thallium(III) Chloride Tetrahydrate, a Redetermination. |journal=Acta Chemica Scandinavica |publisher=Danish Chemical Society |volume=33A |year=1979 |issn=0904-213X |doi=10.3891/acta.chem.scand.33a-0789 |pages=789–794 |doi-access=free}}

:{{chem2|TlI3}} is a black crystalline solid prepared from {{chem2|TlI}} and {{chem2|I2}} in aqueous HI. It does not contain thallium(III), but has the same structure as {{chem2|CsI3}} containing the linear {{chem2|I3-|link=triiodide}} ion.

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. {{chem2|TlCl4-}}.

;{{chem2|TlCl2}}

:This is formulated as {{chem2|Tl^{I}Tl^{III}Cl4}}.

;{{chem2|Tl2Cl3}}

:This yellow compound is formulated {{chem2|Tl^{I}3Tl^{III}Cl6}}.{{cite journal |last1=Böhme |first1=Reinhild |last2=Rath |first2=Jörg |last3=Grunwald |first3=Bernd |last4=Thiele |first4=Gerhard |title=Über zwei Modifikationen von "Tl2Cl3"-valenzgemischten Thallium(I)-hexahalogenothallaten(III) Tl3 [TlCl6] / On Two Modifications of "Tl2Cl3"-Mixed Valence Thallium(I)-hexahalogenothallates(III) |journal=Zeitschrift für Naturforschung B |publisher=Walter de Gruyter GmbH |volume=35 |issue=11 |date=1980-11-01 |issn=1865-7117 |doi=10.1515/znb-1980-1108 |pages=1366–1372 |doi-access=free}}

;{{chem2|Tl2Br3}}

:This compound is similar to {{chem2|Tl2Cl3}} and is formulated {{chem2|Tl^{I}3Tl^{III}Br6}}{{cite journal |last1=Ackermann |first1=Rupprecht |last2=Hirschle |first2=Christian |last3=Rotter |first3=Heinz W. |last4=Thiele |first4=Gerhard |title=Mixed-Valence Thallium(I, III) Bromides The Crystal Structure of α—Tl2Br3 |journal=Zeitschrift für anorganische und allgemeine Chemie |publisher=Wiley |volume=628 |issue=12 |year=2002 |issn=0044-2313 |doi=10.1002/1521-3749(200212)628:12<2675::aid-zaac2675>3.0.co;2-4 |pages=2675–2682 |language=de}}

;;{{chem2|TlBr2}}

:This pale brown solid is formulated {{chem2|Tl^{I}Tl^{III}Br4}}

;;{{chem2|Tl3I4}}

:This compound has been reported as an intermediate in the synthesis of {{chem2|TlI3}} from {{chem2|TlI}} and {{chem2|I2}}. The structure is not known.

;Thallium(I) complexes

:Thallium(I) can form complexes of the type {{chem2|(TlX3)(2-)}} and {{chem2|(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 {{chem2|NaTlF4}} and {{chem2|Na3TlF6}} do not contain discrete tetrahedral and octahedral anions. The structure of {{chem2|NaTlF4}} is the same as fluorite (CaF₂) with {{chem2|Na^{I}}} and {{chem2|Tl^{III}}} atoms occupying the 8 coordinate {{chem2|Ca^{II}}} sites. Na₃TlF₆ has the same structure as cryolite, {{chem2|Na3AlF6}}. In this the thallium atoms are octahedrally coordinated. Both compounds are usually considered to be mixed salts of {{chem2|Na+}} and {{chem2|Tl(3+)}}.

;Thallium(III) chloride complexes

:Salts of tetrahedral {{chem2|TlCl4-}} and octahedral {{chem2|TlCl6(3-)}} are known with various cations.

:Salts containing {{chem2|TlCl5(2-)}} with a square pyramidal structure are known. Some salts that nominally contain {{chem2|TlCl5(2-)}} actually contain the dimeric anion {{chem2|Tl2Cl10(4-)}}, long chain anions where {{chem2|Tl^{III}}} is 6 coordinate and the octahedral units are linked by bridging chlorine atoms, or mixed salts of {{chem2|Tl^{III}Cl4}} and {{chem2|Tl^{III}Cl6}}.{{cite journal |last1=James |first1=Margaret Ann |last2=Clyburne |first2=Jason A.C. |last3=Linden |first3=Anthony |last4=James |first4=Bruce D. |last5=Liesegang |first5=John |last6=Zuzich |first6=Vilma |title=Structural diversity in thallium chemistry: structures of four chlorothallate(III) salts including a novel compound containing three geometrically different anions |journal=Canadian Journal of Chemistry |publisher=Canadian Science Publishing |volume=74 |issue=8 |date=1996-08-01 |issn=0008-4042 |doi=10.1139/v96-166 |pages=1490–1502 |doi-access=free}}

:The ion {{chem2|Tl2Cl9(3−)}}, where thallium atoms are octahedrally coordinated with three bridging chlorine atoms, has been identified in the caesium salt, {{chem2|Cs3Tl2Cl9}}.

;Thallium(III) bromide complexes

:Salts of {{chem2|Tl^{III}Br4−}} and {{chem2|Tl^{III}Br6(3−)}} are known with various cations.

:The {{chem2|TlBr5(2−)}} anion has been characterised in a number of salts and is trigonal bipyramidal. Some other salts that nominally contain {{chem2|TlBr5(2−)}} are mixed salts containing {{chem2|TlBr4(−)}} and {{chem2|Br−}}.{{cite journal |last1=Linden |first1=Anthony |last2=Nugent |first2=Kerry W. |last3=Petridis |first3=Alexander |last4=James |first4=Bruce D. |title=Structural diversity in thallium chemistry |journal=Inorganica Chimica Acta |publisher=Elsevier BV |volume=285 |issue=1 |year=1999 |issn=0020-1693 |doi=10.1016/s0020-1693(98)00339-9 |pages=122–128}}

;Thallium(III) iodide complexes

:Salts of {{chem2|Tl^{III}I4−}} are known. The {{chem2|Tl^{III}}} anion is stable even though the triiodide is a thallium(I) compound.

{{Reflist|25em}}

1. {{Greenwood&Earnshaw}}
2. {{Cotton&Wilkinson6th}}

{{Thallium compounds}}

{{Fluorine compounds}}

Category:Metal halides

Category:Mixed valence compounds

Category:Thallium compounds