Thallium(I) oxide is the inorganic compound of thallium and oxygen with the formula Tl₂O in which thallium is in its +1 oxidation state. It is black and produces a basic yellow solution of thallium(I) hydroxide (TlOH) when dissolved in water. It is formed by heating solid TlOH or Tl₂CO₃ in the absence of air. Thallium oxide is used to make special high refractive index glass. Thallium oxide is a component of several high temperature superconductors. Thallium(I) oxide reacts with acids to make thallium(I) salts.

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Thallium(I) oxide

Names
Other names Thallous oxide
Identifiers
CAS Number	1314-12-1 Y
3D model (JSmol)	Interactive image
ECHA InfoCard	100.013.838
EC Number	215-220-4
PubChem CID	16684203
UNII	LHV2O5DWPQ Y
CompTox Dashboard (EPA)	DTXSID40894900
InChI InChI=1/O.2Tl/q-2;2*+1
SMILES O([Tl])[Tl]
Properties
Chemical formula	Tl2O
Molar mass	424.77 g/mol
Appearance	black orthorhombic crystals hygroscopic
Density	10.45 g/cm3
Melting point	596 °C (1,105 °F; 869 K)
Boiling point	1,080 °C (1,980 °F; 1,350 K) (decomposes)
Solubility in water	soluble (reacts)
Solubility	soluble in alcohol and acid
Structure
Crystal structure	Rhombohedral, hR18[1]
Space group	R-3m, No. 166
Related compounds
Other cations	Thallium(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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Tl₂O adopts the anti-cadmium iodide structure in the solid state.^[1] In this way, the Tl(I) centers are pyramidal and the oxide centers are octahedral.

Thallium(I) oxide, like all thallium compounds, is highly toxic.

Thallium(I) oxide can be produced by decomposition of thallium(I) hydroxide at 100 °C or by heating thallium(III) oxide in the absence of air to 700 °C.^[2]

${\displaystyle \mathrm {2\ TlOH\longrightarrow Tl_{2}O+H_{2}O} }$

${\displaystyle \mathrm {Tl_{2}O_{3}\longrightarrow Tl_{2}O+O_{2}} }$