Osmium borides

Structure of orthorombic 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. 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_1.1, 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 its structure was later reassigned to orthorhombic.^[1][4]

References

1. ^ ^{a b c} Cumberland, Robert W.; et al. (April 27, 2005). "Osmium Diboride, An Ultra-Incompressible, Hard Material". Journal of the American Chemical Society 127 (20): 7264. doi:10.1021/ja043806y. PMID 15898746. 
2. ^ M. Hebbache et al. (2006). "A new superhard material: Osmium diboride OsB2". Solid State Communications 139 (5): 227–231. doi:10.1016/j.ssc.2006.05.041. 
3. ^ Kempter, C. P.; Fries, R. J. (1961). "Crystallography of the Ru-B and Os-B Systems". The Journal of Chemical Physics 34 (6): 1994. doi:10.1063/1.1731807. 
4. ^ Roof, R. B.; Kempter, C. P. (1962). "New Orthorhombic Phase in the Ru-B and Os-B Systems". The Journal of Chemical Physics 37 (7): 1473. doi:10.1063/1.1733309.