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3D model (JSmol)
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PubChem CID
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| Properties | |
| C5O5Os | |
| Molar mass | 330.28 g·mol−1 |
| Appearance | colorless liquid |
| Melting point | 2–2.5 °C (35.6–36.5 °F; 275.1–275.6 K) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
Osmium pentacarbonyl is the organoosmium compound with the formula Os(CO)5. It is the simplest isolatable carbonyl complex of osmium. Osmium pentacarbonyl is a colorless volatile liquid that is obtained by treating solid triosmium dodecacarbonyl under 200 atmospheres of carbon monoxide at 280-290 °C. In contrast, also at 200 atm of CO, solid Ru3(CO)12 converts to Ru(CO)5 at milder temperature of 160 °C.[1]

Samples of Os(CO)5 convert back to the trioosmium cluster upon heating to 80 °C. The analogous conversion of Ru(CO)5 back to Ru3(CO)12 occurs at room temperature.[1] Chlorination of the pentacarbonyl gives a cationic pentacarbonyl complex:[1]
Upon UV irradiation, hexane solutions of the pentacarbonyl react with ethylene to give mono-, di-, and trisubstituted derivatives:[3]