Thallium halides

The thallium halides include monohalides, where thallium has oxidation state +1, trihalides in which thallium generally has oxidation state +3, and some intermediate halides containing thallium with mixed +1 and +3 oxidation states. 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 ZnSe optics are generally only usable to 650 cm−1 (15 μm).

Monohalides

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 mp 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, mp 430 °C. The crystal structure is the same as CsCl.
Thallium(I) bromide
TlBr is a light sensitive, pale yellow crystalline solid, mp 460 °C. The crystal structure is the same as CsCl.
Thallium(I) iodide
At room temperature, TlI is a yellow crystalline solid, mp 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

Thallium bromide iodide ingots

Thallium bromoiodide / thallium bromide iodide (TlBrxI1−x) and thallium bromochloride / 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

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
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
TlCl3 has a distorted Cr(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
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
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

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

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

  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

  1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. 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

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