Osmium(VIII) oxide
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| Names | |||
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Preferred IUPAC name
Osmium tetraoxide
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Systematic IUPAC name
Tetraoxoosmium
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| Other names
Osmium(VIII) oxide
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| Identifiers | |||
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3D model (Jmol)
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| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.040.038 | ||
| EC Number | 244-058-7 | ||
| MeSH | Osmium+tetroxide | ||
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PubChem CID
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| RTECS number | RN1140000 | ||
| UN number | UN 2471 | ||
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| Properties | |||
| OsO4 | |||
| Molar mass | 254.23 g/mol | ||
| Appearance | white volatile solid | ||
| Odor | acrid, chlorine-like | ||
| Density | 4.9 g/cm3 | ||
| Melting point | 40.25 °C (104.45 °F; 313.40 K) | ||
| Boiling point | 129.7 °C (265.5 °F; 402.8 K) | ||
| 5.70 g/100 mL (10 °C) 6.23 g/100 mL (25 °C) |
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| Solubility | 375 g/100 mL (CCl4) soluble in most organic solvents, ammonium hydroxide, phosphorus oxychloride |
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| Vapor pressure | 7 mmHg (20 °C) | ||
| Structure | |||
| Monoclinic, mS20 | |||
| C2/c; a = 0.4515 nm, b = 0.52046 nm, c = 0.80838 nm, α = 77.677°, β = 73.784°, γ = 64.294° | |||
| Hazards | |||
| Safety data sheet | ICSC 0528 | ||
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EU classification (DSD)
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 T+ (T+) C (C) |
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| R-phrases | R26/27/28, R34 | ||
| S-phrases | (S1/2), S7/9, S26, S45 | ||
| NFPA 704 | |||
| Lethal dose or concentration (LD, LC): | |||
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LCLo (lowest published)
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1316 mg/m3 (rabbit, 30 min) 423 mg/m3 (rat, 4 hr) 423 mg/m3 (mouse, 4 hr) |
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| US health exposure limits (NIOSH): | |||
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PEL (Permissible)
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TWA 0.002 mg/m3 | ||
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REL (Recommended)
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TWA 0.002 mg/m3 (0.0002 ppm) ST 0.006 mg/m3 (0.0006 ppm) | ||
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IDLH (Immediate danger)
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1 mg/m3 | ||
| Related compounds | |||
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Other cations
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Ruthenium tetroxide | ||
| Osmium(IV) oxide | |||
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |||
Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite its toxicity and the rarity of osmium. It also has a number of interesting properties, one being that the solid is volatile. The compound is colourless, but most samples appear yellow. This is most likely due to the presence of the impurity OsO2, which is yellow-brown in colour.
Osmium(VIII) oxide forms monoclinic crystals. It has a characteristic acrid chlorine-like odor. The element name osmium is derived from osme, Greek for odor. OsO4 is volatile: it sublimes at room temperature. It is soluble in a wide range of organic solvents. It is also moderately soluble in water, with which it reacts reversibly to form osmic acid (see below).Pure osmium(VIII) oxide is probably colourless and it has been suggested that its yellow hue is due to osmium dioxide (OsO2) impurities. The osmium tetroxide molecule is tetrahedral and therefore non-polar. This nonpolarity helps OsO4 penetrate charged cell membranes. OsO4 is 518 times more soluble in carbon tetrachloride than in water.
The osmium of OsO4 has an oxidation number of VIII, however the metal does not possess a corresponding 8+ charge as the bonding in the compound is largely covalent in character (the ionization energy required to produce a formal 8+ charge also far exceeds the energies available in normal chemical reactions). The osmium atom has eight valence electrons (6s2, 5d6) with double bonds to the four oxide ligands resulting in a 16 electron complex. This is isoelectronic with permanganate and chromate ions.
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