Structure of orthorhombic OsB2. Green atoms are Os, pink – boron
Osmium borides are compounds of osmium and boron. Their most remarkable property is potentially high hardness. It is thought that a combination of high electron density of osmium with the strength of boron-osmium covalent bonds will make osmium borides superhard materials, however this has not been demonstrated yet. For example, OsB2 is hard (hardness comparable to that of sapphire), but not superhard.[1]
Synthesis
Osmium borides are produced in vacuum or inert atmosphere to prevent formation
of osmium tetroxide, which is a hazardous compound. Synthesis occurs at high temperatures (~1000 °C) from a mixture of MgB2 and OsCl3.[1]
Structure
Three osmium borides are known: OsB, Os2B3 and OsB2. The first two have hexagonal structure,[2] similar to that of rhenium diboride. Osmium diboride was first also sought as hexagonal,[3] but one of its phases was later reassigned to orthorhombic.[1][4] In recent methods of synthesis, it has also been found that a hexagonal phase of OsB2 exists with a similar structure to ReB2.[5]
References
^ abcCumberland, Robert W.; et al. (April 27, 2005). "Osmium Diboride, An Ultra-Incompressible, Hard Material". Journal of the American Chemical Society. 127 (20): 7264–5. doi:10.1021/ja043806y. PMID15898746.
