Osmium(Os) reacts with oxygen and sulfur to form oxides and a sulfide of osmium respectively. The oxides are Osmium dioxide with formula OsO2 and osmium tetra oxide with formula OsO4. In the dioxide, osmium combines with two atoms of oxygen, while in the tetra-oxide it combines with four atoms of oxygen. Osmium disulphide has formula Os S2. This means that one atom of osmium combines with two atoms of sulfur. The oxides and sulfide are crystalline in nature.
Osmium reacts extensively with the gas fluorine to form five varieties of fluorides. With the gas chlorine, it forms three varieties of chlorides. The varieties of osmium fluorides are formed with 4, 5, 6, 7 and 8 atoms of fluorine to one atom of Osmium. With chlorine the varieties are formed with 1, 3 and 5 atoms of chlorine to one atom of osmium. Osmium forms so many varieties because of its ability to exist in many oxidation states.
Osmium in oxidation state 4 forms Osmium tetra bromide OsBr4. Osmium tetra bromide readily decomposes at 350 degrees Celsius to form OsBr3 and bromine. In oxidation states 1, 2 and 3 it forms chlorides with formula OsCl, OsCl2, OsCl3. Osmium trichlorideOsCl3 decomposes at 450 degrees Celsius. With Selenium Osmium forms a selenide OsSe2 and a telluride OsTe2 with tellurium.
Osmium seems to have a liking for the carbonyl group(CO), forming at least seven compounds with it. Some examples are Osmium pentacarbonyl Os(CO)5, nonacarbonyl Os2(CO)9, dodecarbonyl Os3(CO)12 and Hexaosmium octadecacarbonyl Os6(CO)18. Osmium complexes are formed when a chloride or bromide of osmium now reacts with hydrogen, sodium, potassium, ammonia or hydroxyl (OH) group.