titanium(II) oxide

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| ImageFile = Titanium(II)-oxide-3D-vdW.png

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| ImageName = Titanium(II) oxide

| IUPACName = Titanium(II) oxide

| OtherNames = Titanium monoxide

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| Section1 = {{Chembox Identifiers

| CASNo = 12137-20-1

| CASNo_Ref = {{cascite|correct|CAS}}

| PubChem = 61685

| SMILES = O=[Ti]

| InChI = 1S/O.Ti

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| Section2 = {{Chembox Properties

| Formula = TiO

| MolarMass = 63.866 g/mol

| Appearance = bronze crystals

| Density = 4.95 g/cm³

| MeltingPtC = 1750

| BoilingPt =

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| Section3 = {{Chembox Structure

| CrystalStruct = cubic

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| Section7 = {{Chembox Hazards

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| FlashPt = Non-flammable

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| Section8 = {{Chembox Related

| OtherAnions =

| OtherCations =

| OtherFunction = Titanium(III) oxide
Titanium(III,IV) oxide
Titanium(IV) oxide

| OtherFunction_label = titanium oxides

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Titanium(II) oxide (TiO) is an inorganic chemical compound of titanium and oxygen. It can be prepared from titanium dioxide and titanium metal at 1500 °C.{{Holleman&Wiberg}} It is non-stoichiometric in a range TiO_0.7 to TiO_1.3 and this is caused by vacancies of either Ti or O in the defect rock salt structure. In pure TiO 15% of both Ti and O sites are vacant, as the vacancies allow metal-metal bonding between adjacent Ti centres. Careful annealing can cause ordering of the vacancies producing a monoclinic form which has 5 TiO units in the primitive cell that exhibits lower resistivity.{{cite journal | last1=Banus | first1=M. D. | last2=Reed | first2=T. B. | last3=Strauss | first3=A. J. | title=Electrical and Magnetic Properties of TiO and VO | journal=Physical Review B | publisher=American Physical Society (APS) | volume=5 | issue=8 | date=1972-04-15 | issn=0556-2805 | doi=10.1103/physrevb.5.2775 | pages=2775–2784| bibcode=1972PhRvB...5.2775B }} A high temperature form with titanium atoms with trigonal prismatic coordination is also known.{{Greenwood&Earnshaw2nd}} Acid solutions of TiO are stable for a short time then decompose to give hydrogen:

:2 Ti²⁺(aq) + 2 H⁺(aq) → 2 Ti³⁺(aq) + H₂(g)

Gas-phase TiO shows strong bands in the optical spectra of cool (M-type) stars.{{Cite web|url=http://www.stsci.edu/~inr/ldwarf.html|title = Spectral classification of late-type dwarfs}} In 2017, TiO was claimed to be detected in an exoplanet atmosphere for the first time; a result which is still debated in the literature. Additionally, evidence has been obtained for the presence of the diatomic molecule TiO in the interstellar medium.{{cite journal | last1=Dyck | first1=H. M. | last2=Nordgren | first2=Tyler E. | title=The Effect of TiO Absorption on Optical and Infrared Angular Diameters of Cool Stars | journal=The Astronomical Journal | publisher=American Astronomical Society | volume=124 | issue=1 | year=2002 | issn=0004-6256 | doi=10.1086/341039 | pages=541–545| bibcode=2002AJ....124..541D | s2cid=117642107 | doi-access=free }}