page_title: Tellurium
section_title: Compounds
hierarchical_section_title: Tellurium / Compounds
caption_attribution_description: English: Tellurium dioxide
context_page_description: Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth, and partly to tellurium's low affinity for oxygen, which causes it to bind preferentially to other chalcophiles in dense minerals that sink into the core.
  Tellurium-bearing compounds were first discovered in 1782 in a gold mine in Kleinschlatten, Transylvania by Austrian mineralogist Franz-Joseph Müller von Reichenstein, although it was Martin Heinrich Klaproth who named the new element in 1798 after the Latin word for "earth", tellus. Gold telluride minerals are the most notable natural gold compounds.
context_section_description: Tellurium belongs to the chalcogen (group 16) family of elements on the periodic table, which also includes oxygen, sulfur, selenium and polonium: Tellurium and selenium compounds are similar. Tellurium exhibits the oxidation states −2, +2, +4 and +6, with +4 being most common.
  Tellurides
  Reduction of Te metal produces the tellurides and polytellurides, Teₙ²⁻. The −2 oxidation state is exhibited in binary compounds with many metals, such as zinc telluride, ZnTe, produced by heating tellurium with zinc. Decomposition of ZnTe with hydrochloric acid yields hydrogen telluride (H
  ₂Te), a highly unstable analogue of the other chalcogen hydrides, H
  ₂O, H
  ₂S and H
  ₂Se:
  ZnTe + 2 HCl → ZnCl
  ₂ + H
  ₂Te
  H
  ₂Te is unstable, whereas salts of its conjugate base [TeH]⁻ are stable.
  Halides
  The +2 oxidation state is exhibited by the dihalides, TeCl
  ₂, TeBr
  ₂ and TeI
  ₂. The dihalides have not been obtained in pure form, although they are known decomposition products of the tetrahalides in organic solvents, and the derived tetrahalotellurates are well-characterized:
  Te + X
  ₂ + 2 X⁻
   → TeX²⁻
  ₄
  where X is Cl, Br, or I. These anions are square planar in geometry. Polynuclear anionic species also exist, such as the dark brown Te
  ₂I²⁻
  ₆, and the black Te
  ₄I²⁻
  ₁₄.
  Fluorine forms two halides with tellurium: the mixed-valence Te
  ₂F
  ₄ and TeF
  ₆. In the +6 oxidation state, the –OTeF
  ₅ structural group occurs in a number of compounds such as HOTeF
  ₅, B(OTeF
  ₅)
  ₃, Xe(OTeF
  ₅)
  ₂, Te(OTeF
  ₅)
  ₄ and Te(OTeF
  ₅)
  ₆. The square antiprismatic anion TeF²⁻
  ₈ is also attested. The other halogens do not form halides with tellurium in the +6 oxidation state, but only tetrahalides (TeCl
  ₄, TeBr
  ₄ and TeI
  ₄) in the +4 state, and other lower halides (Te
  ₃Cl
  ₂, Te
  ₂Cl
  ₂, Te
  ₂Br
  ₂, Te
  ₂I and two forms of TeI). In the +4 oxidation state, halotellurate anions are known, such as TeCl²⁻
  ₆ and Te
  ₂Cl²⁻
  ₁₀. Halotellurium cations are also attested, including TeI⁺
  ₃, found in TeI
  ₃AsF
  ₆.
  Oxocompounds
  Tellurium monoxide was first reported in 1883 as a black amorphous solid formed by the heat decomposition of TeSO
  ₃ in vacuum, disproportionating into tellurium dioxide, TeO
  ₂ and elemental tellurium upon heating. Since then, however, existence in the solid phase is doubted and in dispute, although it is known as a vapor fragment; the black solid may be merely an equimolar mixture of elemental tellurium and tellurium dioxide.
  Tellurium dioxide is formed by heating tellurium in air, where it burns with a blue flame. Tellurium trioxide, β-TeO
  ₃, is obtained by thermal decomposition of Te(OH)
  ₆. The other two forms of trioxide reported in the literature, the α- and γ- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of Te⁴⁺
  , OH⁻
   and O⁻
  ₂. Tellurium also exhibits mixed-valence oxides, Te
  ₂O
  ₅ and Te
  ₄O
  ₉.
  The tellurium oxides and hydrated oxides form a series of acids, including tellurous acid (H
  ₂TeO
  ₃), orthotelluric acid (Te(OH)
  ₆) and metatelluric acid ((H
  ₂TeO
  ₄)
  ₙ). The two forms of telluric acid form tellurate salts containing the TeO2–
  ₄ and TeO⁶⁻
  ₆ anions, respectively. Tellurous acid forms tellurite salts containing the anion TeO²⁻
  ₃.
  Zintl cations
  When tellurium is treated with concentrated sulfuric acid, the result is a red solution of the Zintl ion, Te²⁺
  ₄. The oxidation of tellurium by AsF
  ₅ in liquid SO
  ₂ produces the same square planar cation, in addition to the trigonal prismatic, yellow-orange Te⁴⁺
  ₆:
  4 Te + 3 AsF
  ₅ → Te²⁺
  ₄(AsF⁻
  ₆)
  ₂ + AsF
  ₃
  6 Te + 6 AsF
  ₅ → Te⁴⁺
  ₆(AsF⁻
  ₆)
  ₄ + 2 AsF
  ₃
  Other tellurium Zintl cations include the polymeric Te²⁺
  ₇ and the blue-black Te²⁺
  ₈, consisting of two fused 5-membered tellurium rings. The latter cation is formed by the reaction of tellurium with tungsten hexachloride:
  8 Te + 2 WCl
  ₆ → Te²⁺
  ₈(WCl⁻
  ₆)
  ₂
  Interchalcogen cations also exist, such as Te
  ₂Se²⁺
  ₆ (distorted cubic geometry) and Te
  ₂Se²⁺
  ₈. These are formed by oxidizing mixtures of tellurium and selenium with AsF
  ₅ or SbF
  ₅.
  Organotellurium compounds
  Tellurium does not readily form analogues of alcohols and thiols, with the functiona
caption: A sample of tellurium dioxide powder
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