|Molar mass||Molar mass::254.23 g/mol|
|Appearance||clear or pale yellow translucent solid|
|CAS number||CAS number::20816-12-0|
|Density and phase||[[Density::4.91 g/cm3]], solid|
|Solubility in water||6 g/100 ml (25°C)|
|Melting point||Melting point::40.25°C|
|Boiling point||Boiling point::129.7°C|
|MSDS||Material safety data sheet|
|Main hazards|| Highly toxic (T+)
|R/S statement|| R: R26/27/28, R34 |
S: (S1/2), S7/9, S26, S45
|Related osmium oxides||Osmium(IV) oxide|
| Except where noted otherwise, data are given for|
materials in their standard state (at 25 °C, 100 kPa)
Disclaimer and references
Osmium tetroxide is the most well-known, important, and easily prepared compound of Osmium. Osmium tetroxide is a unique compound due to its few volatile oxides of a heavy metal and its controllable oxidizing agent, the Osmium is octavalent. Osmium tetroxide is one of the highest oxidations achieved by a transition element. Osmium tetroxide has a tetrahedral geometry and the combination of high toxicity and high volatility, meaning that it is easily evaporated. This makes Osmium tetroxide harmful and dangerous if not handled correctly. 
Osmium tetroxide is made up of pale yellow-brown crystalline structures, mostly solid, and possesses similar characteristics of ozone, acrid odor. Osmium tetroxide is extremely soluble with inert organic solvents, as well as with water. It is especially very soluble in CCl4(carbon tetrachloride = tetrachloromethane). The name Osmium comes from a Greek word osme, meaning odor. Pure Osmium tetroxide is usually colorless and pale yellow is shown translucently because of its impurities. It has a tetrahedral molecular shape with the O-Os-O bonds angles at about 109.5°, just like Methane (CH4). Because Osmium tetroxide is tetrahedral it is non-polar. Its nonpolarity allows it to go through charged cell membranes.   At room temperature, Osmium tetroxide exists as liquid, and is automatically formed when Osmium is exposed to air.
Osmium tetroxide is a combination of highly volatile and highly toxic. Osmium tetroxide is a special solid because, generally, solids do not convert directly into a gas at room temperature. Because it’s highly toxicity, it can be very useful when both reacting and damaging living tissues. It also penetrates skin and mucous membranes, being relatively small and water soluble. 
OsO4 When combined with alkaline aqueous solution:
OsO4 + 2 NaOH → Na2[cis-OsO4(OH)2] + O2
When combined with NH3, nitride-oxide is formed:
OsO4 + NH3 + KOH → K[Os(N)O3] + 2 H2O
The [Os(N)O3]- anion is electronic and is structural with OsO4. Using primary amine tert-BuNH2 one obtains the corresponding imides derivative:
OsO4 + 4 Me3CNH2 → Os(NCMe3)4 + 4 H2O
OsO4 undergoes "reductive carbonization" in methanol at 400 K and 200 bar of pressure to produce the triangular cluster Os3(CO)12:
3 OsO4 + 24 CO → Os3(CO)12 + 12 CO2
In this reaction osmium changes oxidation state by eight units. 
Osmium tetroxide is formed when Osmium powder meets oxygen of the air, reacting slowly and giving off detectable amount of Osmium tetroxide vapor. The foundation of Osmium tetroxide, Osmium, is found bonded to other platinum. Osmium can be found in South Africa, California, and Oregon.  After crude platinum by oxidative acid distillation and separation from ruthenium, Osmium tetroxide compound is formed industrially. The compound is best made in the laboratory by direct oxidation of osmium metal, or by acid distillation with chlorate (the inorganic group ClO 3 or a compound containing it) of almost any Osmium compound. 
Osmium tetroxide was discovered in 1803 by Smithson Tennant, who was born in 1761 and died in 1815. In 1803, Smithson Tennant stated, "a pungent and peculiar smell . . . from the extrication of a very volatile metal oxide; and, as this smell is one of its most distinguishing characters, I should on that account incline to call this metal Osmium," when treating fusion with alkali of the black residue.  In 1803, Smithson Tennant discovered Osmium using aqua regia, a mixture of hydrochloric and nitric acids. He discovered that there is a black powder left out when the element platinum is dissolved in aqua regia. After his experiment in 1804, Tennant called the black powder a mixture of two new elements, which are Indium and Osmium. The name Osmium came from the unusual smell of Osmium tetroxide. Meaning 'royal water', aqua regia helped to discover Osmium and Indium. The Greek word 'osme', meaning 'odor', is the foundation of the name of Osmium. 
The value of Osmium tetroxide has been known and applied since 1913, and is now being used as one of the major industrial and laboratory compounds, particularly for reactions of steroids and sugars. It is the smoothest and most efficient reagent(a chemical substance that is used to create a reaction in combination with some other substance) known, and mainly used with olefin double bonds to give glycols(any of a class of organic compounds belonging to the alcohol family). Osmium tetroxide tends to react best and fastest with strained olefins(unsaturated chemical compound containing at least one carbon-to-carbon double bond).
Osmium tetroxide compound is widely used for study of cells and tissues. Its unique characteristics enable it to fix and stain biological materials. This is useful for visible or electron microscopy of biological materials. Osmium tetroxide is highly toxic even in small concentrations and considered as a potential chemical weapon. 
Osmium tetroxide can be used as catalytic amount of the shapeless examination for amino-alcohols. When the compound is added to Sodium periodate, it can be used for oxidative cleavage of alkenes(Alkenes are oxidative cleaved to alts of carboxylic acids, by hot basic permanganate solutions).
OsO4 is used as a staining agent to contrast the images and, as a lipid stain, to sputter coating. When it is combined with a heavy metal, Osmium tetroxide creates high secondary emission, obscuring details of the cell membrane. Osmium tetroxide can quickly kill specimen like protozoa; therefore; it is helpful to fix biological samples when combined with HgCl2.
A gold crystalline solid, Osmeth is formed after Osmium tetroxide is recycled and complex with hexamine. It does not emit toxically substances unlikely the pure Osmium tetroxide. This can be used as a working solution of OsO4.
Osmium tetroxide needs to be detoxified for its proper disposal and spill decontamination.
Osmium tetroxide must be treated by an expert because it is harmful and toxic. It causes irritation, burns, rashes, and green to black stain immediately after it is exposure to skin. When a person breathes the odor, it can cause irritation for nose, wheezing, nosebleeds, cough, and tightness in the chest, sore throat, and hoarseness. When eyes are contacted with Osmium tetroxide it can be very dangerous. It causes redness and swelling; blurred vision; and, at the worst, permanent vision loss. The eye pain is is described to be 'burning' immediately after Osmium tetroxide contacts the eyes.
There also can be long-term effects after exposure from Osmium tetroxide. It can cause genetic changes, and further studying is needed whether or not it possesses cancer or reproductive hazard. Since Osmium tetroxide causes irritation to lungs, the repeated exposure develops coughing, and shortness of breath. It also damages kidneys and bothers the urinary system.
Ways of reducing exposure
There are few ways to get away from these problems. Before handling Osmium tetroxide, make sure safety gear is on. It is best not to contact with Osmium tetroxide, therefore wearing protective gloves and clothing is required. All gear must be clean all the time and be worn before handling the compound. For eye protection, wear side shields or goggles; face shield along goggles and contact lenses must not be worn when treating this compound. When exposed, wash off immediately with water. Post hazard and warning signs around working areas help observers to pay attention while working on the compound.
- Osmium Tetroxide and Its Applications By W.P.Griffith Department of Inorganic Chemistry, Imperial College, London 1974
- Osmium tetroxide 1997-2011 CHEMIE.DE Information Service GmbH
- OsO4 by Dr Mike Thompson Winchester College, UK May 2004
- Osmium tetroxide - Oxidizer...of death! Smith IC, Carson BL, Ferguson TL. Osmium: an appraisal of environmental exposure. Environ Health Perspect. 1974 Aug;8:201-13
- Osmium - Os 1998-2009 Lenntech Water treatment & purification Holding B.V
- Chemistry Explained Foundation and Applications:Osmium Advameg, Inc. 2007-2010
- How to Detoxify Osmium Tetroxide by an eHow Contributor 1999-2011
- Hazardous substance fact sheet by New Jersey Department of Health and Senior Services used in Feburary 6th, 2011